Powertrain Control Module (PCM) is the Engine Computer. It takes in numerous sensor values, then runs the spark plugs and fuel injectors among other things. Its main purpose is to control and monitor tail pipe emissions. It has nothing to do with GPS. That's an OnStar / big brother thing with GM cars.
The PCM does have the capability to detect a whole bunch of problems with sensors and other things related to the engine and set diagnostic fault codes into its memory. If the detected problem(s) could affect emissions, it will turn in the Check Engine light. Your mechanic can connect a hand-held computer called a scanner to read the fault codes. They will direct him to the circuit or system with the problem, not necessarily the defective part. Over time, the computer learns the characteristics of the engine and its sensors and will continually make fuel and spark timing adjustments. It runs emission reducing equipment too.
There are entire service manuals devoted to nothing else but diagnosing the systems run by the computer. To simplify it to my story here is like saying the only thing your home computer is good for is sending e-mail and displaying pretty pictures.
Chrysler used the first Engine Computer in 1977 on some engines. They became standard equipment in 1983.
Tuesday, March 23rd, 2010 AT 2:16 AM