What is a PCM?
By JEREMY PROOME on Jul 14, 2025The PCM is a powertrain control module, which is an integral component in a vehicle that controls and manages the engine and transmission. The role of the PCM is to ensure that the engine is operating optimally, controlling fuel injectors, ignition coils, fuel consumption, and emissions.
How does a PCM work?
The PCM receives information and signals from the car’s many sensors, and adjusts and operates the engine powertrain in relation to these signals. Things like how much an accelerator pedal has been pushed, the emissions coming out of the exhaust, and how much fuel is being used, help the PCM adjust the performance of a vehicle’s engine (and the timing of gear-changes in an automatic).
In an ideal situation, the PCM will receive clean and accurate information from the other onboard computers and sensors, therefore controlling the engine and transmission as effectively as possible to result in a smooth and seamless ride. This will get the most out of your car and power of your vehicle’s engine.
Why do PCMs go wrong?
Like other onboard monitoring and control systems, PCMs are prone to malfunctioning, because there is sadly a lot that can go wrong with any car.
Due to the fact that PCMs rely heavily on the working state of all the sensors, if they’re not firing and functioning properly, the PCM won’t work well. For example, the oxygen sensor in the exhaust system could be inaccurate or broken, and this would cause the PCM to fail to adjust the air-fuel mixture for the engine.
How do you know if your PCM isn’t working?
There are some telltale signs that your PCM isn’t working properly, such as symptoms from your vehicle not starting, the check-engine light turning on, weak accelerator power, unstable engine function, erratic gear changes (with an automatic), engine stalling, and poor fuel economy.
What to do if your PCM stops working?
If your Powertrain Control Module (PCM) stops working, it’s best to avoid operating the vehicle and get the PCM tested and diagnosed as soon as possible. The relevant sensors that trigger the PCM will also need to be assessed to ensure they’re working correctly. It’s best to use professionals with expertise to diagnose, and then repair or replace a damaged PCM.
Mail in automotive electronic repair services
The ECU Pro offers an affordable mail-in repair service for automotive electronics. To have your unit repaired, simply remove the part and mail it to us. Our professional team will either test, repair, or clone your unit.
Our team has over 30 years experience in automotive electronic repairs. We specialize in German vehicles such as BMW, Mercedes and Mini. Our main focus is engine control unit repairs ( ECU, PCM or DME). Our state of the art facility has over 30 test vehicles to ensure that all parts are tested in actual vehicles before being returned to our clients.
Most of the services we provide is plug and play and doesn't require any additional coding.
