Depending on the type of vehicle, a failure in the powertrain control module may cause transmission problems. A failed PCM may also lead to numerous other issues, such as problems with the charging system, emissions controls or in communicating with the other onboard control modules.
Some of the more common signs that the powertrain control module has failed or is defective include poor engine performance or the vehicle stalling while driving. It may also cause the vehicle not to start or stay running. A failed PCM may also cause the check engine light to be illuminated and show unrepairable diagnostic codes or show several unrelated codes at the same time.
The powertrain control module is basically the brain of the engine control system, so when it fails, it can affect any and all parts that the microprocessor controls. This includes the ignition system, fuel injection and also the antilock brakes and automatic transmissions on some vehicle models. The PCM is sometimes referred to as the engine control module, or ECM, although the ECM technically only controls the engine, while the PCM controls the engine and transmission.
In some newer vehicles, the PCM requires regular software updates to keep functioning properly.