This bulletin applies to 2008 Chevy Cobalt vehicles equipped with the 4T45E transmission (including both non-BAS Hybrid and BAS Hybrid models).
The customer may have a complaint of a chuggle or stall when coming to a stop. The vehicle will restart. This may be caused by a momentary applied torque converters causing excessive loads on the engine.
If this condition is experienced on a BASH Hybrid, the engine tachometer will drop to zero and not Auto Stop. There would not be a command for an auto-stop. The engine may restart using the 12V starter and set a DTC P1A6F. This may lead the technician to incorrectly suspect the hybrid components.
A partially or momentarily applied TCC may be caused by a restriction in the transmission cooling system. A possible restriction in the transmission cooling system may not allow a sufficient volume of fluid to properly release the TCC.
In order to properly diagnose for a possible restriction, use J45096 or equivalent to flow test the transmission oil cooler pipes. If the flow rate is below minimum, check the following areas:
- Transmission cooler for restriction
- Transmission cooler lines for bends/kinks
- Transmission cooler line fluid passages (behind the fittings) for any restriction