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PCM (Power Train Control Module)

There are a few different systems in place for computerized control of a vehicle’s engine, transmission, and some driveline components, depending on the make, model, or year of a vehicle. One system calls for an engine control module (ECM) and a transmission control module (TCM), while another type of system will use one integrated, computerized controller called the powertrain control module (PCM).

 

The PCM is an especially powerful computer that manages or monitors the engine’s ignition system, fuel injection, emission systems, mechanical positioning of the rotating assembly, exhaust system, transmission, and any other functions related to the operation of the engine and transmission. In some vehicles, it may also control the operation of the traction control system (TCS) and the anti-lock brake system (ABS).

 

Many dislike the complication that comes with computerized vehicles, but computerized systems make engines run much more efficiently, alert drivers of issues before they lead to catastrophic failure, and offer reference to technicians that takes the guesswork out of auto repair.

 

The main interaction that drivers have with the powertrain control module is the check engine light, and various other warning lights on the instrument panel. The PCM is programmed from the factory to use these warning lights to alert the driver of failure when certain conditions are met. For instance, the check engine light will illuminate if the engine coolant temperature is too high, or too low. These lights alert drivers to issues, but they alert technicians that diagnostic trouble codes (DTC) are stored in the PCM for retrieval and diagnosis. This is a very helpful in the diagnosis and repair arena, as long as the proper computerized tools are used.

 

Symptoms of Wear or Failure of the PCM (Power Train Control Module)

  • Check Engine Light illuminates with codes that cannot be repaired are stored. When the PCM detects an issue, but no issue exists, the PCM may have failed, and is reading erroneously.
  • Several unrelated trouble codes are set simultaneously. When these DTC’s are stored from unrelated components, especially when there is no fault found, a technician will begin to diagnose the PCM before moving on with diagnosing the trouble codes.
  • Vehicle may not start or run
  • Poor engine performance
  • Engine stalls while driving

Related Repair Advice

  • Many vehicles have upgradeable software in their PCMs, so be sure to check for any Technical Service Bulletins (TSBs) that pertain to possible problems
  • When replacement is required, use a new factory PCM and install the latest software. This will likely require a trip to an authorized service center for your brand of vehicle. (Kia, Chevrolet, etc..)
  • A PCM can be mistakenly replaced when there was actually a defective engine sensor that was overlooked in the initial diagnosis. To prevent this, professional technicians will follow a flow chart when diagnosing a trouble code.
  • The terms PCM and ECM/U (engine control module/unit) are commonly used interchangeably. Technically, the ECM controls only engine-related functions, while the PCM controls engine and transmission operation.
  • The PCM and other electronic components should not be removed while the battery is connected. If the PCM is functioning properly, this could cause it to fail.
  • Using jumper cables to recharge the battery can be especially dangerous to the PCM, and other electronic controllers on the vehicle. For instructions on how to properly jump-start a vehicle, see here.

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