Q: What's the difference between the ECM and PCM?

The engine control module (ECM) controls all the engine functions to keep it running correctly monitoring all the sensors of the engine. The power train control module (PCM) will include multiple control modules in one case called a PCM. The PCM will include the ECM and one or more other control modules like anti-lock brakes, transmission, speed control, cooling fan controls, antithief and any other system the manufacture wants to include in the PCM housing. Your PCM is programmed to only work with your other control modules in your vehicle. Your vehicle will not start and run if your new PCM is not programmed by the proper programming scanner approved by the manufacturer. You may need to go to an approved service provider or dealer to have the new PCM programmed so your keys will start the truck. If you need to have a mechanic like one from YourMechanic diagnose the PCM to see if it is the cause of your problem you are having or there is another problem then make an appointment to have a mechanic come to you.