They can then analyze the error codes and tell you the nature of the problem. If the engine misfires a lot or backfires, it can mean a variety of issues so it’s best to take your car to the mechanic. But it could also indicate problems with the transmission valve body or simply being low on transmission fluid. If the car starts shifting unnecessarily, it’s a reasonable indication that something is wrong with your PCM or TCM. If this is not corrected quickly, it will emit too much carbon and adversely affect the engine’s performance as well. What you will notice is an increase in emissions and a decrease in fuel economy. If there’s too much fuel, though, the engine won’t be damaged straight away. If this continues over an extended period, the engine could become permanently damaged since it is not getting the lubrication it needs. It will start to jerk and possibly even stall. If there’s too little fuel, the engine won’t function properly. It could misinterpret the air/fuel mix, for example, and not send the engine the necessary amount of fuel. Your PCM might not be at risk of the flu, but when it’s “sick,” the mechanism is going to make errors. It’s easy to make the wrong decisions and make mistakes. If you’re fatigued or ill, you have a kind of brain fog that makes it harder to think. When you’re tired, you don’t operate at peak efficiency. In the meantime, here are six classic symptoms to diagnose a PCM problem. They have specialized equipment that allows them to read the error codes that the PCM is emitting. The best way to diagnose an issue with this system is to go to a qualified auto-electrician. It could mean throwing your timing and other vital systems out, too. Problems with this system mean that it can’t send messages to other systems within the vehicle. It is the car’s brain, and it controls everything in the vehicle.Ī bad car computer is a big deal. It doesn’t matter if you own a Ford or a Chevy, the PCM relay will be similar.