What Are the Symptoms of a Bad Powertrain Control Module?

by Jen Davis
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The powertrain control module, otherwise known as the PCM or computer, is essentially your vehicle's brain. The PCM in your car or truck is designed to control and regulate all of its functions and parts. Problems in the computer can lead to serious problems with almost every aspect of your car or truck because the computer has to work properly in order for everything else to follow suit.

Running Poorly

The PCM is what ultimately controls and regulates your fuel system. Different sensors in the engine send the PCM data about what the engine is doing. The PCM then adjusts the fuel mixture based on this data. If the PCM is not working properly, odds are that the fuel mixture will not be right. The vehicle may be receiving too much fuel or too little. If it is not getting enough fuel, it will cough, choke, sputter and may even stall. If it is getting too much fuel, your fuel economy will decrease and your exhaust emissions will increase.

Will Not Run

In some cases, a PCM problem will cause the vehicle not to run at all. The PCM's functions include positioning the crankshaft and controlling the ignition spark and timing. If there are problems with how the PCM performs these functions, the vehicle will not run and may even incur damage.

Dashboard Error Lights

If your PCM is malfunctioning, you can expect to see almost every error light imaginable appear and disappear at some point. The PCM controls and interprets sensor readings, so if it is not doing this properly, you can expect to see your "Check Engine" light, your "ABS system" light and a variety of others flash on and off.


The PCM controls your vehicle's fuel and emissions system. If your PCM is not functioning properly, your car may fail its emissions test, emit too much smoke, emit colored exhaust (white, blue or black, depending on the issue) and may smell like fuel.

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