The PCM is designed to maintain exhaust emission levels to Federal/California/other standards while providing excellent Driveability and fuel efficiency. A problem in any one of theses systems will result in a check engine light and codes stored in memory. PCM location is determined by the make, model and year of your vehicle. You would need to get specific wiring diagrams for your vehicle to determine location.
Review the components and wiring diagrams in order to determine which systems are controlled by the PCM. The PCM monitors numerous engine and vehicle functions. The following are some of the functions that the PCM controls: • The engine fueling • The ignition control (IC) • The knock sensor (KS) system • The evaporative emissions (EVAP) system • The secondary air injection (AIR) system (if equipped) • The exhaust gas recirculation (EGR) system • The automatic transmission functions • The generator • The A/C clutch control • The cooling fan control
Powertrain Control Module Function.
The PCM constantly looks at the information from various sensors and other inputs and controls systems that affect vehicle performance and emissions. The PCM also performs diagnostic tests on various parts of the system.
The PCM can recognize operational problems and alert the driver via the malfunction indicator lamp (MIL). When the PCM detects a malfunction, the PCM stores a diagnostic trouble code (DTC). The problem area is identified by the particular DTC that is set. The control module supplies a buffered voltage to various sensors and switches. The input and output devices in the PCM include analog-to-digital converters, signal buffers, counters, and output drivers. The output drivers are electronic switches that complete a ground or voltage circuit when turned on. Most PCM controlled components are operated via output drivers. The PCM monitors these driver circuits for proper operation and, in most cases, can set a DTC corresponding to the controlled device if a problem is detected.
Note: A flashing check engine light is a government specific function that indicates the engine has a misfire that is severe enough to cause catalytic converter damage. Quick diagnosis and repair are needed to prevent catayltic converter failure to avoid this costly repair.
Although it is common for a mechanic or any individual to blame the computer for any specific problem on a car or truck, the fact is that aside from certain situations, the PCM is not normally the cause. Maybe because it is easy to just blame a computer or it still is thought as a 'black box', or people just do not understand how a vehicle system works. The fact is that most computer related problems are caused by failed sensors or bad wiring.
Connection problems at sensors are a common cause of a check engine light. Also remember that one system can effect another, so finding the root cause of a problem may fix multiple problems at once.
Don't just jump to the conclusion of a bad computer because a problem is hard to diagnose. Proper knowledge of a particular system, proper diagnostic tools such as wiring schematics and electrical test equipment are required to properly diagnose todays car and trucks.