It has been posted that some have used the "disconnect battery" method to clear codes or reset the ECM.
This bulletin is out today that talks about a no start condition that could occur in these cases. It may be key specific, also.
Quote:
Subject: Engine Wont Crank After Battery Disconnect, Dead Battery Condition or After A Reprogramming Event, Theft Deterrent Light Illuminated, DTC Stored, (Reprogram Keys into Theft Deterrent Module)
Models: 2006 Chevrolet Cobalt, HHR
2006 Pontiac Pursuit (Canada Only), Solstice
2007 Saturn SKY Built Prior to June 30, 2006
Condition
Some customers may comment on the following conditions after experiencing a loss of battery power in their vehicle. Technicians may encounter a vehicle with the following conditions after disconnecting a battery during a service procedure or after reprogramming any module on the vehicle.
• The engine will not crank using the key the customer currently has in their possession.
• If the customer has both keys, one key starts the vehicle but the vehicle will not crank using the second key.
• The Theft Deterrent Light may be illuminated during the no crank condition.
Technicians may find Diagnostic Trouble Code (DTC) for "Unprogrammed Transponder Identification Code Received" stored as a current or a history code.
Cause
This condition may be caused by the failure of the key programming information for both keys to be permanently stored in the Theft Deterrent Module (TDM). The information for one key is stored permanently while the information for the other key will be lost if the vehicle's battery voltage drops below 7.8 volts.
The failure condition will also occur when the key programming information for one of the vehicle's keys is lost after a battery disconnect during a service procedure, a dead battery condition or after a reprogramming event for any module and the key that has lost its programming is used to start the vehicle. The vehicle's other key programming information will not be lost due to the loss of battery voltage or a reprogramming event and that key will still start the vehicle. It may also be possible to unknowingly render the customer's second key inoperative after a battery disconnect or a reprogramming event performed during other service procedures on the vehicle.
It is recommended that the customer be asked for both keys to their vehicle when their vehicle is brought in for any service requests in which a battery disconnect or reprogramming event will occur. Technicians should verify that both keys work before returning the vehicle to the customer.
Correction
Reprogram the keys into the Theft Deterrent Module.
Important: In order to prevent the technician from possibly having to perform a very long diagnostic procedure, every effort should be made to obtain both keys to the vehicle before any repairs are attempted on the vehicle. If the customer only brings in one key, their second key will no longer start the vehicle after these repairs are completed unless the second key is programmed into the TDM at a later date using the Adding Keys procedure. Having both keys available will also prevent the possible situation where the second key cannot be programmed into the TDM and the vehicle would have to be returned to the dealership again.
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition.
So another tip would be to always have all keys available if the car is going in for service under these conditions.
Yes, I know a car will not start with a dead battery anyways. Lets assume that "after a dead battery event" means that the battery has been charged back up to the proper levels.
