See Figure 1
The engine computer, which controls the fuel injection system on the vehicles covered by this guide, is referred to as the Powertrain Control Module (PCM). The PCM is a digital computer containing a microprocessor. The PCM receives input signals from various switches and sensors that are referred to as engine computer inputs. Based on these inputs, the PCM adjusts various engine and vehicle operations through devices referred to as outputs.
The PCM inputs are as follows:
The PCM outputs are as follows:
Based on inputs it receives, the PCM adjusts fuel injector pulse width, idle speed, ignition timing and canister purge operation. The PCM regulates the cooling fans, air conditioning and speed control systems. The PCM changes the alternator charge rate by adjusting the generator field.
The ASD relay and fuel pump relay are mounted externally, but turned on and off by the PCM. The camshaft and crankshaft signals are sent to the PCM. If the PCM does not receive both signals within approximately one second of engine cranking, it deactivates the ASD and fuel pump relays. When these relays are deactivated, the power is shut off to the fuel injectors, ignition coils, fuel pump and heating element in each oxygen sensor.
The PCM contains a voltage converter that changes battery voltage to a regulated 8.0 volts. The 8.0 volts power the camshaft position sensor, crankshaft position sensor and vehicle speed sensor. The PCM also provides a 5.0 volt supply for the coolant temperature sensor, intake air temperature sensor and throttle position sensor.