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My 2007 Solstice with 2.4 motor and automatic transmission has started downshifting into 4th or 3rd when where is no pressure on on drive train (will shift on level roads). It then will not up shift into overdrive. This may happen every 50 to 400 miles. No pattern to the happening. I can stop the car, shut the engine off for 4 to 6 minutes, start back up and usually everything is fine. Trans is solid with no slipping and smooth shifting. Have replaced TCM (transmission control module) and the torque convertor. No change. Has anyone had this problem?
Rob Penn needs help!!
 

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You don't mention it so i assume there is no service engine light.
 

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You don't mention it so i assume there is no service engine light.
There has been no service lights or faults show up. Also the trans has been reprogramed.
Thanks JohnWR for your response. I am a short distance south of you.
 

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I have had some time to study the service manual and have a few thoughts.
  • The only failures that come close to this are the shift solenoid valves sticking, but that failure also includes free-running in fifth, and/or soft shifts into fifth, neither of which you describe
  • You could have a problem with the shifter. The shifter is just an electrical selector switch that tells the TCM what gear mode you want to use. If it is internally in "4" instead of "D" the transmission will not shift into fifth.
  • A switch problem inside the shifter could cause this problem, but it seems more likely to trigger a code.
  • Diagnosing this may require a diagnostic scanner, like a Tech2, to find out what the TCM is trying to do as opposed to what it is doing.
 

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Discussion Starter #5
I have had some time to study the service manual and have a few thoughts.
  • The only failures that come close to this are the shift solenoid valves sticking, but that failure also includes free-running in fifth, and/or soft shifts into fifth, neither of which you describe
  • You could have a problem with the shifter. The shifter is just an electrical selector switch that tells the TCM what gear mode you want to use. If it is internally in "4" instead of "D" the transmission will not shift into fifth.
  • A switch problem inside the shifter could cause this problem, but it seems more likely to trigger a code.
  • Diagnosing this may require a diagnostic scanner, like a Tech2, to find out what the TCM is trying to do as opposed to what it is doing.
I would consider purchasing a diagnostic scanner to connect to my Solstice. Which scanner do you recommend and what will it read or diagnose in TMC (which has been replaced) or other electrical problems can be monitored. Can the scanner be connected and left until the problem occurs again?
 

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I am only aware of two scanner options that will help here, but there may be others.

The Tech2 is the device that GM service people use for diagnosis. A "real" one costs $3k +, but Chinese "clones" are available for around $500, or were at least a few years ago. I have a clone, and it appears to be just like a real one, although it took two tries to get them to ship one that was fully functional.

A VCX Nano is a device that uses a version of GM's Tech2Win to emulate a Tech2 on a computer. I have one that i never really got to work well, but others have had good success with them.

Either of these can communicate with any of the control modules in the car, force things on and off, and do a limited amount of setup. Some programming requires a connection to the internet to access GM's TIS2WEB to get the files needed to flash a module. Access to that is by a subscription that is very reasonably priced if you are only working on one car. I haven't done that myself, but I have read reports from some who have.
 
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