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Discussion Starter · #1 ·
I have found an article that goes in detail about troubleshooting this code. The issue however is that it makes references to diagrams and schematics on a paid website which i can not open.

Among other things, it appears the issue can happen if the TPS sensors 1 and 2 disagree on their readings, the system will throw a CEL. It is possible to be an ECM issue.

In the article, it suggests testing certain pins of the throttle body connector and the ECM for voltage and resistance.

**
Does anyone have the diagram to tell me which pin is what letter for the throttle body and the ECM?
**

Also in HPTunners i can see that my 2 sensors clearly disagree on throttle position.

1) Ignition on, engine off. APP = 0.
I found it intereting that at rest TP(SAE) is 32% and TP1 vs TP2 are 18% off.
Font Material property Screenshot Parallel Rectangle


As soon as I give it just a little throttle TP(SAE) drops from 32% to 20%. Not sure if that is normal
Rectangle Font Parallel Screenshot Number


100% pedal
Rectangle Font Material property Parallel Screenshot


50% pedal
Rectangle Font Parallel Screenshot Number
 

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Discussion Starter · #2 ·
I found the pin diagram for the TB and followed the troubleshooting procedure.
I found no shorts or resistance issues. This means I need a new throttle body.

At this point, I think I could actually upgrade for something with a larger diameter.
Any suggestions on what would be a good option for an upgrade?
I have a 2006 Pontiac solstice 2.4 that is turbocharged. I have an 8pin connector.
 

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you have the largest TB that you can attach without getting into a custom intake manifold.
 
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I'm not sure how it works on the Kappas but many electronic throttle pedals send an inverse signal on each of 2 wires. Meaning that when one wire sends a 100% signal, the other one should send a 0% signal. Depending if our ECMs show actual or interpreted readings, it would be normal for both pedal positions to be different.

Let's wait to hear from other members whether they know how the Solstice ECM reports the pedal data -- is it the raw signal from the pedal wires (readings would always be different from each other except at around 50%) or is it the interpreted signal (readings should be the same)?

Do you have a GXP or NA, and what year is it?
 

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Discussion Starter · #5 · (Edited)
I have replaced the Throttle Body and it seems the issue is still there.
One of the troubleshooting steps in the file I previously attached reads:

Verify the scan tool TP sensor 1 voltage is less than 0.1
- if greater than .1 test the signal circuit terminal D for a short to voltage, if the circuit tests normal, replace the ECM.

HP tuners reads sensor 1 voltage at 3.94 and sensor 2 voltage 1.06 (both throttle bodies)

Even if 1 is #2 in HP Tuners the voltage is not close to 0.1

I have tested the circuit for a short with volt meter by connecting one lead to the pin and another to a common ground. i read nothing.

I suppose the next step is to replace the ECM.

This brings a whole bunch of questions now:
  • would i benefit from installing a different (upgraded ECM)? Maybe the one that is in GXP? or just get the same i have (12223209)
  • install something aftermarket that is reasonably priced.
  • i know HPTunners credits work with one car unless you buy unlimited for the model or generation of cars. I have a single car license. Do I need to purchase more credits for the new ECU now or there is a way to transfer?
 

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Here is the test procedure for the throttle body.

connect meter red test lead to pin "D" which is a dark green wire
connect meter black test lead to pin "C" which is a tan wire

KOEO (Key On Engine Off) The voltage should read about 4 volts. Depress accelerator to WOT and watch the meter. The voltage should drop to around 1v. It should be a nice smooth sweep and no drop outs or spikes in voltage

connect meter red test lead to pin "F" which is a purple wire
connect meter black test lead to pin "C" which is a tan wire

KOEO (Key On Engine Off) The voltage should read about 1 volt. Depress accelerator to WOT and watch the meter. The voltage should increase to somewhere between 3.5 and 4.0 volts. It should be a nice smooth sweep and no drop outs or spikes in voltage


If the voltage is out of range or no voltage appears on the meter

connect meter red test lead to pin "C" which is a tan wire
connect meter black test lead to a known good ground
KOEO the voltage should be 0.10 or less

connect meter red test lead to pin "E" which is a tan or gray wire
connect meter black test lead to a known good ground

KOEO the voltage should be between 4.5 and 5.0 volts

To check the throttle actuator you would need an oscilliscope as the signal feeding the actuator is a PWM signal.
 

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Discussion Starter · #7 · (Edited)
Here is the test procedure for the throttle body.

connect meter red test lead to pin "D" which is a dark green wire
connect meter black test lead to pin "C" which is a tan wire

KOEO (Key On Engine Off) The voltage should read about 4 volts. Depress accelerator to WOT and watch the meter. The voltage should drop to around 1v. It should be a nice smooth sweep and no drop outs or spikes in voltage

connect meter red test lead to pin "F" which is a purple wire
connect meter black test lead to pin "C" which is a tan wire

KOEO (Key On Engine Off) The voltage should read about 1 volt. Depress accelerator to WOT and watch the meter. The voltage should increase to somewhere between 3.5 and 4.0 volts. It should be a nice smooth sweep and no drop outs or spikes in voltage


If the voltage is out of range or no voltage appears on the meter

connect meter red test lead to pin "C" which is a tan wire
connect meter black test lead to a known good ground
KOEO the voltage should be 0.10 or less

connect meter red test lead to pin "E" which is a tan or gray wire
connect meter black test lead to a known good ground

KOEO the voltage should be between 4.5 and 5.0 volts

To check the throttle actuator you would need an oscilliscope as the signal feeding the actuator is a PWM signal.
KG, I read 0V between both points. Are your instructions for a 6 pin connector by any chance? because mine is 8pin.
Attached are pictures of wires and pins i used for testing.

Also i assumed the following pinout scheme from my previous research:
ABCD
EFDH

From my original post though you can see that at 0% throttle
TPS1: 3.92V
TPS2: 1.02V

At 100% throttle:
TPS1: 0.59V
TPS2: 4.39V

Value changes were smooth .
The derived percentage between the two though is drastically different at times and is greater than 6% which is what I believe is a threshold to throw a code.
At 50% throttle, for instance, according to the throttle pedal sensor, TPS1 was at 87% and TPS2 was at 34%.
 

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Discussion Starter · #8 ·
KG, I read 0V between both points. Are your instructions for a 6 pin connector by any chance? because mine is 8pin.
Attached are pictures of wires and pins i used for testing.

Also i assumed the following pinout scheme from my previous research:
ABCD
EFDH

From my original post though you can see that at 0% throttle
TPS1: 3.92V
TPS2: 1.02V

At 100% throttle:
TPS1: 0.59V
TPS2: 4.39V

Value changes were smooth .
The derived percentage between the two though is drastically different at times and is greater than 6% which is what I believe is a threshold to throw a code.
At 50% throttle, for instance, according to the throttle pedal sensor, TPS1 was at 87% and TPS2 was at 34%.
Procedure followed:

1)Ignition off
- tested no resistance on C vs GROUND.

2)Ignition ON
- E + GROUND = 5V

3)
Test for infinite resistance between TP sensor 1 signal circuit terminal D and TP sensor 2 signal circuit
terminal F.
- PASS.

4)Correction of my previous post where i stated the following produced 1 volt. I believe the test calls for harnes to be disconnected from the Throttle body. So with harnes disconnected from throttle body:
Verify the scan tool TP sensor 1 voltage is less than 0.1 volt.
actual: HPTunners reads TPS1: 0.0V or TPS2: 4.98V
- This is a PASS

5)Install a 3A fused jumper wire between the signal circuit terminal D and the 5-volt reference circuit
terminal E of the TP sensor 1, verify the TP sensor 1 voltage is greater than 4.8 volts.
HPTunners reads:
TPS1:4.98V
TPS2:4.98V <- instructions don't call for the value of the TP2, not sure if it should stay at 4.98V

If all circuits test normal, replace the throttle body:
  • I tried a different one and the TPS1% vs TPS2% still seem to have a very large discrepancy..
  • additionally, the car idles at like 1.5-2k RPM with this new TB..
 

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You have to remap the voltage to get the range.

new_value = (((value - old_min) * (new_max - new_min)) / (old_max - old_min)) + new_min

where
new_min = 0
new_max = 100
old_min = voltage at 0 throttle
old_max = voltage at 100% throttle
value = voltage reading from TPS


From my original post though you can see that at 0% throttle
TPS1: 3.92V
TPS2: 1.02V

At 100% throttle:
TPS1: 0.59V
TPS2: 4.39V


new_value = (((value - 0) * (0.59- 3.92)) / (100- 0)) + 3.92


new_value = (((value - 0) * (4.39- 1.02)) / (100- 0)) + 1.02



so for TPS1 this is the equation

new_value = (((value - 3.92) * (100-0)) / (0.59- 3.92)) + 0


and for TPS2
new_value = (((value - 1.02) * (100- 0)) / (4.39- 1.02)) + 0


if you have a pair of voltages for the TPS sensors I can tell you if they are off from each other.

I can tell you that at 50% throttle the voltages should be reading

TPS1: 2.255v
TPS2: 2.705v

Those equations above convert the voltage range into a percentage. so the percentages need to be within a specific tolerance.


Here is the information I have on throttle position sensor correlation



DTC P0120, P0122, P0123, P0220, P0222, P0223, Or P2135


Diagnostic Instructions

  • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
  • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
  • Diagnostic Procedure Instructions provides an overview of each diagnostic category.


DTC Descriptors
  • P0120: Throttle Position (TP) Sensor 1 Circuit
  • P0122: Throttle Position (TP) Sensor 1 Circuit Low Voltage
  • P0123: Throttle Position (TP) Sensor 1 Circuit High Voltage
  • P0220: Throttle Position (TP) Sensor 2 Circuit
  • P0222: Throttle Position (TP) Sensor 2 Circuit Low Voltage
  • P0223: Throttle Position (TP) Sensor 2 Circuit High Voltage
  • P2135: Throttle Position (TP) Sensor 1-2 Correlation

Diagnostic Fault Information

DTC P0120, P0122, P0123, P0220, P0222, P0223, or P2135


Circuit Short toGroundHigh ResistanceOpenShort to VoltageSignal Performance
TP Sensor 1 SignalP0122P2135P0122P0123P0068, P0121
TP Sensor 1 5-Volt ReferenceP0122P2135P0122P0123
TP Sensor 1 Low ReferenceP2135P0123
TP Sensor 2 SignalP0222P2135P0223P0223P0068, P0121
TP Sensor 2 5-Volt ReferenceP0222P2135P0222P0223
TP Sensor 2 Low ReferenceP2135P0223



Typical Scan Tool Data

TP Sensor 1

Parameter Normal Range: 0.27-4.67 V
CircuitShort to GroundOpenShort to Voltage
TP Sensor 1 Signal0V0V5V
TP Sensor 1 5-Volt Reference0V0V5V
TP Sensor 1 Low Reference5V



TP Sensor 2
Parameter Normal Range: 0.31-4.7 V
CircuitShort to GroundOpenShort to Voltage
TP Sensor 2 Signal0V5V5V
TP Sensor 2 5-Volt Reference0V0V5V
TP Sensor 2 Low Reference5V


Circuit/System Description

The throttle actuator control (TAC) system uses 2 throttle position (TP) sensors to monitor the throttle position. The TP sensors 1 and 2 are located within the throttle body assembly.
Each sensor has the following circuits:
  • A 5-volt reference circuit
  • A low reference circuit
  • A signal circuit

Two processors are also used to monitor the TAC system data. Both processors are located within the engine control module (ECM). Each signal circuit provides both processors with a signal voltage proportional to throttle plate movement. Both processors monitor each other's data to verify that the indicated TP calculation is correct.


Conditions For Running The DTC
  • P0120, P0122, P0123, P0220, P0222, P0223
    • The system voltage is more than 5.23 volts.
    • The ignition is in the Unlock/Accessory or Run position.
    • DTC P0641 is not set.
    • DTCs P0120, P0122, P0123, P0220, P0222, P0223 run continuously when the above conditions are met.
  • P2135
    • The system voltage is more than 5.23 volts.
    • The ignition is in the Unlock/Accessory or Run position.
    • DTCs P0120, P0220, P0641, P0651 are not set.
    • DTC P2135 runs continuously when the above conditions are met.


Conditions For Setting The DTC

  • P0120: TP sensor 1 voltage is less than 0.27 volt or more than 4.67 volts for more than 0.5 second.
  • P0122: The ECM detects that the TP sensor 1 voltage is less than 0.27 volt for more than 0.4 second.
  • P0123: The ECM detects that the TP sensor 1 voltage is more than 4.67 volts for more than 0.4 second.
  • P0220: The TP sensor 2 voltage is less than 0.31 volt or more than 4.7 volts for more than 0.5 second.
  • P0222: The ECM detects that the TP sensor 2 voltage is less than 0.31 volt for more than 0.4 second.
  • P0223: The ECM detects that the TP sensor 2 voltage is more than 4.7 volts for more than 0.4 second.
  • P2135: The difference between the TP sensor 1 and TP sensor 2 exceeds a predetermined value for more than 2 seconds.

Action Taken When The DTC Sets

  • DTC P0120, P0122, P0123, P0220, P0222, P0223, and P2135 are Type A DTCs.
  • The control module commands the TAC system to operate in the Reduced Engine Power mode.
  • A message center or an indicator displays Reduced Engine Power.
  • Under certain conditions, the control module commands the engine OFF.

Conditions For Clearing The MIL/DTC
DTC P0120, P0122, P0123, P0220, P0222, P0223, and P2135 are Type A DTCs.


Circuit/System Verification

  1. Ignition ON, observe the TP sensor 1 voltage parameter. The reading should be between 0.27-4.67 volts and change with accelerator pedal input.
  2. Ignition ON, observe the TP sensor 2 voltage parameter. The reading should be between 0.31-4.7 volts and change with accelerator pedal input.
  3. Observe the TP sensor 1 and 2 parameter. The scan tool should indicate agree.
  4. Clear the DTCs with the scan tool. Operate the vehicle within the Conditions for Running the DTC, or within the conditions that you observed from the Freeze Frame/Failure Records.
  5. Verify that DTC P0120 or P0220 are not the only throttle position DTCs set.
    1. If DTC P0120 or P0220 are the only DTCs set, replace the control module.
  6. Verify that DTCs P0641 or P0651 are set.
    1. If DTC P0641 or P0651 is set, refer to DTC P0641 or P0651 .


Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the throttle body. Allow sufficient time for the ECM to completely power down.
  2. Ignition OFF, test for less than 5 ohms of resistance between each low reference circuit terminal B and G and ground.
    1. If greater than 5 ohms, test the affected low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  3. Ignition ON, test for 4.8-5.2 volts between each 5-volt reference circuit terminal C and ground, and terminal H and ground.
    1. If less than 4.8 volts, test the affected 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
    2. If greater than 5.2 volts, test the affected 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  4. Verify the scan tool TP sensor 1 voltage is less than 0.1 volt.
    1. If greater than 0.1 volt, test the signal circuit terminal A for a short to voltage. If the circuit tests normal, replace the ECM.
  5. Verify the scan tool TP sensor 2 voltage is greater than 4.8 volts.
    1. If less than 4.8 volts, test the signal circuit terminal D for a short to ground. If the circuit tests normal, replace the ECM.
  6. Install a 3A fused jumper wire between the signal circuit terminal A and the 5-volt reference circuit terminal C of the TP sensor 1, verify the TP sensor 1 voltage is greater than 4.8 volts.
    1. If less than 4.8 volts, test the TP sensor 1 signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
  7. Install a 3A fused jumper wire between the signal circuit terminal D and the low reference circuit terminal B of the TP sensor 2, verify that the TP sensor 2 voltage is less than 0.1 volt.
    1. If greater than 0.1 volt, test the TP sensor 2 signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
  8. Ignition OFF, disconnect the harness connector at the ECM.
  9. Test for less than 5 ohms of resistance on all TP sensor circuits between the following terminals:
    1. ECM C2 5-volt reference circuit terminal 44 to terminal C.
    2. ECM C2 5-volt reference circuit terminal 44 to terminal H.
    3. ECM C2 signal circuit terminal 64 to terminal A.
    4. ECM C2 signal circuit terminal 64 to terminal D.

      If greater than 5 ohms, repair the affected circuit.
  10. Test for infinite resistance between TP sensor 1 signal circuit terminal A and TP sensor 2 signal circuit terminal D.
    1. If less than infinite resistance, repair the short between TP sensor 1 signal circuit and TP sensor 2 signal circuit.
  11. If all circuits test normal, replace the throttle body.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
  • Control Module References
  • Throttle Body Assembly Replacement





Here is the information I have on throttle position performance.



Diagnostic Instructions
  • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
  • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
  • Diagnostic Procedure Instructions provides an overview of each diagnostic category.

  • DTC Descriptors

    DTC P0068: Throttle Body Airflow Performance
    DTC P0121: Throttle Position (TP) Sensor 1 Performance


    Circuit/System Description

    The engine control module (ECM) uses the following information to calculate an expected airflow rate:
    • The throttle position (TP)
    • The barometric pressure (BARO)
    • The manifold absolute pressure (MAP)
    • The intake air temperature (IAT)
    • The engine RPM
    • The mass air flow (MAF)

  • Conditions For Running The DTC
    • DTCs P0641, P0651, P1516, P2101, P2119, P2176 are not set.
    • The engine is running and the engine speed is more than 600 RPM.
    • DTC P0068 and P0121 run continuously when the above conditions are met.



  • Conditions For Setting The DTC

    The ECM detects that the airflow rate is more than the calculated airflow for more than 0.2 second.
    Action Taken When The DTC Sets
    • DTC P0068 is a Type A DTC.
    • DTC P0121 is a Type B DTC.
    • The control module commands the TAC system to operate in the Reduced Engine Power mode.
    • A message center or an indicator displays Reduced Engine Power.
    • Under certain conditions the control module commands the engine OFF.

  • Conditions For Clearing The MIL/DTC
    • DTC P0068 is a Type A DTC.
    • DTC P0121 is a Type B DTC.

  • Circuit/System Testing
    1. Inspect for the following conditions:
      1. Vacuum hoses for splits, kinks, and proper connections as shown on Vehicle Emission Control Information label
      2. Inspect thoroughly for any type of leak or restriction
      3. Air leaks at throttle body mounting area and intake manifold sealing surfaces
    2. Allow the engine to reach operating temperature. Observe the Manifold Absolute Pressure (MAP) Sensor Voltage parameter with a scan tool. Voltage should be more than 0.8 volt and less than 4 volts.
      1. If more than 4 volts or less than 0.8 volt, refer to DTC P0106 .
    3. Idle the engine. Observe the MAP Sensor kPa parameter with a scan tool. Increase the engine speed slowly and then back to idle. The MAP sensor kPa should change smoothly and gradually as engine speed is increased and returned to idle.
      1. If the MAP sensor kPa does not change refer to DTC P0106 .
    4. Take a snapshot of the engine data list while performing the actions listed below. The MAF sensor kPa should change smoothly and gradually as the engine speed is increased and is returned to idle.
      1. Idle the engine.
      2. Increase the engine speed slowly to 3,000 RPM, then back to idle.
      3. Exit from the snapshot and review the data.
      4. Observe the Mass Air Flow (MAF) Sensor parameter frame by frame with a scan tool. The MAF sensor g/s should change smoothly and gradually as the engine speed is increased and is returned to idle.
    5. If the MAF sensor g/s does not change smoothly and gradually as the engine speed is increased and is returned to idle refer to DTC P0101 or P1101 .
    6. Inspect the throttle body for the following conditions:
      1. Loose or damaged throttle blade
      2. Broken throttle shaft
      3. Any throttle body damage
    7. If any of these conditions exist, replace the throttle body assembly.


  • Repair Procedures

    Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    • Throttle Body Assembly Replacement
    • Control Module References for ECM replacement, setup, and programming



    Throttle Actuator Control (TAC) System Description
    Purpose


    The throttle actuator control (TAC) system delivers improved throttle response and greater reliability and eliminates the need for mechanical cable.

    The TAC system performs the following functions:
    • Accelerator pedal position (APP) sensing
    • Throttle positioning to meet driver and engine demands
    • Throttle position (TP) sensing
    • Internal diagnostics
    • Cruise control functions
    • Manage TAC electrical power consumption

  • The TAC system includes the following components:
    • The APP sensors
    • The throttle body assembly
    • The engine control module (ECM)

  • Accelerator Pedal Position (APP) Sensor

    The accelerator pedal contains 2 individual accelerator pedal position (APP) sensors within the assembly.

    The APP sensors 1 and 2 are potentiometer type sensors each with 3 circuits:
    • A 5-volt reference circuit
    • A low reference circuit
    • A signal circuit

  • The APP sensors are used to determine the pedal angle. The engine control module (ECM) provides each APP sensor a 5-volt reference circuit and a low reference circuit. The APP sensors provide the ECM with signal voltage proportional to the pedal movement. The APP sensor 1 signal voltage at rest position is near the low reference and increases as the pedal is actuated. The APP sensor 2 signal voltage at rest position is also near the low reference and increases as the pedal is actuated.

    Throttle Body Assembly

    The throttle assembly contains the following components:
    • The throttle blade
    • The throttle actuator motor
    • The throttle position (TP) sensor 1 and 2

  • The throttle body functions similar to a conventional throttle body with the following exceptions:
    • An electric motor opens and closes the throttle valve.
    • The throttle blade is spring loaded in both directions and the default position is slightly open.
    • There are 2 individual TP sensors within the throttle body assembly.

  • The TP sensors are used to determine the throttle plate angle. The TP sensors provide the engine control module (ECM) with a signal voltage proportional to throttle plate movement. The TP sensor 1 signal voltage at closed throttle is near the 5-volt reference and decreases as the throttle plate is opened. The TP sensor 2 signal voltage at closed throttle is near the low reference and increases as the throttle plate is opened.


    Engine Control Module

    The engine control module (ECM) is the control center for the throttle actuator control (TAC) system. The ECM determines the drivers intent and then calculates the appropriate throttle response. The ECM achieves throttle positioning by providing a pulse width modulated voltage to the TAC motor.


    Modes Of Operation
    • Normal Mode

      During the operation of the throttle actuator control (TAC) system, several modes or functions are considered normal.

      The following modes may be entered during normal operation:
      • Minimum pedal value-At key-up the engine control module (ECM) updates the learned minimum pedal value.
      • Minimum throttle position (TP) values-At key-up the ECM updates the learned minimum TP value. In order to learn the minimum TP value, the throttle blade is moved to the closed position.
      • Ice break mode-If the throttle is not able to reach a predetermined minimum TP, the ice break mode is entered. During the ice break mode, the ECM commands the maximum pulse width several times to the throttle actuator motor in the closing direction.
      • Battery saver mode-After a predetermined time without engine RPM, the ECM commands the battery saver mode. During the battery saver mode, the TAC module removes the voltage from the motor control circuits, which removes the current draw used to maintain the idle position and allows the throttle to return to the spring loaded default position.
    • Reduced Engine Power Mode

      When the ECM detects a condition with the TAC system, the ECM may enter a reduced engine power mode.

      Reduced engine power may cause one or more of the following conditions:
      • Acceleration limiting-The ECM will continue to use the accelerator pedal for throttle control; however, the vehicle acceleration is limited.
      • Limited throttle mode-The ECM will continue to use the accelerator pedal for throttle control; however, the maximum throttle opening is limited.
      • Throttle default mode-The ECM will turn off the throttle actuator motor and the throttle will return to the spring loaded default position.
      • Forced idle mode-The ECM will perform the following actions:
        • Limit engine speed to idle by positioning the throttle position, or by controlling the fuel and spark if the throttle is turned OFF.
        • Ignore the accelerator pedal input.
      • Engine shutdown mode-The ECM will disable fuel and de-energize the throttle actuator.
 

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I don't see anything that specifies any kind of a percentage value between the 2 TPS sensors. If they both do not report a spot on percentage of the range for how open the throttle plate is them the car will go into limp mode. The second TP sensor is only there as a way to verify the first sensors is functioning properly. It's the same thing for the accelerator pedal position sensor. There is more then one of them to be able to check the validity of the primary sensor.
 

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If you add the TP1 voltage and the TP2 voltage together you will get the maximum voltage.

so in the example of the throttle being 50% open

TPS1: 2.255v
TPS2: 2.705v

2.255 + 2.705 = 4.96

It is juts a mechanism for error checking. I believe the standard is a 200 millivolt (0.2 volts) deviation which is a 4% deviation. so 0.2 volts above or below the 5.0 volts and a DTC gets set.
 

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Discussion Starter · #12 · (Edited)
Thank you KG, very detailed instructions.

Interesting that a vacuum leak is one of the major items for p0121.

below are 3 screenshots taken at 11psi 0.6psi and vacuum.
Instructions are saying that throttle position is calculated based on the MAF flow and compared against TP1 and TP2
I suppose Throttle position SAE is based on MAF? Could you please confirm?
If that is the case SAE reeds less under boost compared to TP1 around the same at 0psi and more under vacuum.
That makes sense if i have a leak.. i looked at vacuum lines and gaskets and everything seems alright.
I'm wondering if there is a trick of some kind to pinpoint which seal is leaking.

Also TP2 percentage is always way off from SAE and TP1. The voltage of TP1+TP2 however is always around 4.94-5V. So i dont know if there is another problem here. Previously you mentioned that my ECU has checksum issues. I never saw that error code again.

Also attaching HPTunners file if you have any interest looking at it:
 

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I believe that your throttle body is fine. So long as the TP1 and TP2 voltages add up to to be close to 5.0 volts then it is working as it should.

The code you had given earlier was for a bad checksum in the memory of the ECM. Now this is not usually a problem because their is "backup" memory. So there is memory that is extra that gets used for the sole purpose of acting as a replacement should a block of memory go bad. If you continue to have the checksum faults then there would be a concern. Most times those checksum errors go unnoticed because the DTC gets cleared after so many key cycles.

Stop using the "Throttle Position" and "Throttle Position 2" channels. They are not reporting correctly and you are getting all messed up because of it. Use the SAE throttle position as this is going to be a corrected throttle position that will show 100% when the accelerator is pushed to the floor. The accelerator pedal position sensor in reality cannot get to 100, it can only get to something like 96% I believe. The throttle plate is also not able to open to 100% either. It's just the way the mechanical bits in those parts work.

I am not sure as to why you think you have a vacuum leak. If you want to check to see if you have one then go to the parts store and pick yourself up a can of "Brake Kleen". Make sure it is made by CRC and says "Brake Kleen" on the can. You want to be wearing eye protection when you do this and the engine MUST be cold. I cannot stress how important it is for the engine to be cold. Start the car, if the RPMs are elevated then tap the accelerator a few times. That will cause the RPMs to drop. Use the red straw that comes with the Brake Kleen and spray every single vacuum hose connection, all of the charge pipe connections and the intake pipe connections. Be easy with how hard you push down on the nozzle of the Brake Kleen. That stuff comes out something crazy and it will splash everywhere. You might want to give it a couple of shots against a piece of cardboard so you can get the feel for it.

If there is a vacuum leak where you are spraying the engine RPMs will jump up. Brake Kleen is highly volatile and that is why the engine MUST be cold when you do this.

Also spray the intake manifold to head interface and also the throttle body to intake manifold interface. Be careful with the throttle body as you do not want to soak it. It's not like a frogs ass, it's not 100% water tight.

You don't need a lot of Brake Kleen to cause the engine RPMs to go up. If you want to test it shoot a little into the air cleaner, this way you know how much is needed to cause a change in the RPMs and also how fast the RPMs change from when you spray it.
 

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Discussion Starter · #14 ·
I bought a can of CRC Brake Kleen and sprayed it directly into the air intake filter and the car did not care a bit ))
I suppose it could be the material that the filter is made of or maybe the fumes diffused while traveling through the turbo and the intercooler.

Either way, I sprayed in 1-sec bursts of 3-4 at each spot around MAF all around before and after TB and at the head to manifold connection next to each cylinder. No change in RPM.

So at this point, I don't know what my next step should be:

p0121
1) Check for leaks.
- none observed
2)Observe MAP sensor voltage is within range.
- Yes.
3)Observe MAP sensor value change gradually with an increased or decreased load.
- I see it fluctuating within +/- 1 kPa, but the general dynamic follows the load.
4/5) Observed MAF lb/sec changes gradually with an increased or decreased load.
- I see it fluctuating within +/- 1lb but the general dynamic follows the load.
6)Examine the throttle body.
- TB is fine. Tried new TB. no change.


Repair procedure:
- Control Module References for ECM replacement - what is that? ECM replacement?
 

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I bought a can of CRC Brake Kleen and sprayed it directly into the air intake filter and the car did not care a bit ))
I suppose it could be the material that the filter is made of or maybe the fumes diffused while traveling through the turbo and the intercooler.

Either way, I sprayed in 1-sec bursts of 3-4 at each spot around MAF all around before and after TB and at the head to manifold connection next to each cylinder. No change in RPM.

So at this point, I don't know what my next step should be:

p0121
1) Check for leaks.
- none observed
2)Observe MAP sensor voltage is within range.
- Yes.
3)Observe MAP sensor value change gradually with an increased or decreased load.
- I see it fluctuating within +/- 1 kPa, but the general dynamic follows the load.
4/5) Observed MAF lb/sec changes gradually with an increased or decreased load.
- I see it fluctuating within +/- 1lb but the general dynamic follows the load.
6)Examine the throttle body.
- TB is fine. Tried new TB. no change.


Repair procedure:
- Control Module References for ECM replacement - what is that? ECM replacement?
The ECM (Engine Control Module) is the computer that controls the engine. It is located on the left side of the car near the firewall. You can try removing and reinserting the connectors a few times to clean the contacts.
 

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This is what I have on the P0121 DTC and I want to target into some specific things about this.

Conditions For Running The DTC
  • The system voltage is more than 7 volts.
  • The TP sensor 1 voltage is between 0.18-4.63 volts.
  • DTC P0121 runs continuously when the above conditions are met.

Conditions For Setting The DTC P0121
  • The TP sensor 1 disagrees more than 6.3 percent from TP sensor 2 for over 140 ms.
  • The TP sensor 1 disagrees more than 9 percent from the throttle position calculated from mass air flow (MAF) signal for over 280 ms.


Action Taken When The DTC Sets
  • DTC P0121 is a Type B DTC.
  • The control module commands the TAC system to operate in the Reduced Engine Power mode.
  • A message center or an indicator displays Reduced Engine Power.



Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the throttle body. Allow sufficient time for the ECM to completely power down.

  2. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal C and ground.
    1. If greater than 5 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

  3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal E and ground.
    1. If less than 4.8 volts, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

    2. If greater than 5.2 volts, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.

  4. Verify the scan tool TP sensor 1 voltage is less than 0.1 volt.
    1. If greater than 0.1 volt, test the signal circuit terminal D for a short to voltage. If the circuit tests normal, replace the ECM.

  5. Install a 3A fused jumper wire between the signal circuit terminal D and the 5-volt reference circuit terminal E of the TP sensor 1, verify the TP sensor 1 voltage is greater than 4.8 volts.
    1. If less than 4.8 volts, test the TP sensor 1 signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

  6. Ignition OFF, disconnect the harness connector at the ECM.

  7. Test for less than 5 ohms of resistance on the TP sensor circuits between the following terminals:
    1. ECM C1 5-volt reference circuit terminal 39 to terminal E.

    2. ECM C1 signal circuit terminal 90 to terminal D.
      1. If greater than 5 ohms, repair the affected circuit.

  8. Test for infinite resistance between TP sensor 1 signal circuit terminal D and TP sensor 2 signal circuit terminal F.
    1. If less than infinite resistance, repair the short between TP sensor 1 signal circuit and TP sensor 2 signal circuit.

  9. If all circuits test normal, replace the throttle body.


There are 2 things that cause this DTC to get set. They are:

The TP sensor 1 disagrees more than 6.3 percent from TP sensor 2 for over 140 ms.

OR

The TP sensor 1 disagrees more than 9 percent from the throttle position calculated from mass air flow (MAF) signal for over 280 ms.

We do not know which one is causing the problem. But we can find out by looking at the freeze frame data the ECM stores when the DTC gets set. That freeze frame data will contain the sensor readings.

There is also some very specific steps in the testing procedure that have to be done to determine what the problem is I will explain the steps and what they are testing for.


2. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal C and ground.
  1. If greater than 5 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
This is testing the 5 volt power supply circuit. The "low reference" circuit in the ECM is a known low signal. what I mean by "known" is it is created by the ECM or the circuitry inside of the ECM. Where as the ground in the vehicle is not known as the ECM did not create it. Make sense?? It can be used as a reliable way to get measurements.

If the resistance is greater then 5 ohms then test the circuit. This would be the wiring between the throttle body and the ECM. If the resistance test on the wire checkes out as normal then the ECM is no good and needs to be replaced. If the wire is either open or has a resistance of > 5 ohms then the wiring between the throttle body and the ECM is the problem and needs to be fixed.



3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal E and ground.
  1. If less than 4.8 volts, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

  2. If greater than 5.2 volts, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
This step the 5v output from the ECM gets tested to ensure it is within spec.
The spec states that the 5V output should not be lower then 4.8 volts and not higher then 5.2 volts. Remember that 0.2 volts I mentioned is the SAE spec? 5.0 V +- 0.2 volts is the 4.8 to 5.2 if the voltage is outside of that window there are 2 more tests to be done. Both tests are done on the wiring in the car to verify that is not the cause and if the wiring is not the cause then the ECM is no good.


4. Verify the scan tool TP sensor 1 voltage is less than 0.1 volt.
  1. If greater than 0.1 volt, test the signal circuit terminal D for a short to voltage. If the circuit tests normal, replace the ECM.
This is checking the signal coming out of the sensor. Connect the scan tool and get the voltage reading for TP sensor 1. It should be at or below 0.1 volts. Remember this is with the throttle body unplugged. So if the reading is higher then 0.1 volts the problem lies in either the wiring or the ECM itself. That is why the next test is to test the circuit (wiring) to make sure there isn't a short in the harness. If the wiring checks out normal then the ECM is bad.



I am not going to go over all of them. I wanted to explain the first couple this way you would understand the vocabulary and what it is that is being looked for and why the result would be a bad ECM.

so when it says to "test the circuit" it really means is test the wiring between the sensor and the ECM. I don't remember if you have access to the wiring diagrams for the car. If not let me know. In order to test the circuits you need to know the pinning at the ECM.



Here is an example of what a broken wire between the throttle body and the ECM an do. This person did the EXACT same thing you did with buying a new throttle body and the problem persisted.



you need to perform the tests listed above to isolate the cause of the problem. I know doing this is really technical and has vocabulary most people are not familiar with. It is easier for me to explain these things over the phone. If you want to do it over the phone so I can walk you through the entire testing process I can do that. Send me a PM if that is what you want to do. I have done this for several members of the forum and isolate the cause of their problem so they could repair it. I have 100% success rate doing this with people. It might take more then one phone call if you don't have the proper tools needed to do the testing and that's fine. I will only know if you have the proper tools when we start the diagnostic.

the electrical diagnostic portion of a vehicle is so complex to diagnose it is a whole lot easier to do it over the phone. There is simply too much to type out and explain. I already have callouses on the tips of my fingers from typing out the long ass posts. My fingers would want to fall off if I had to key out an entire step by step to diagnose this problem.
 
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