General System Description

PCM:

DESCRIPTION
The PCM is responsible for maintaining proper spark and fuel injection timing for all driving conditions. Ignition Control (IC) spark timing is the PCM method of controlling spark advance and ignition dwell. To provide optimum driveability and emissions, the PCM monitors input signals from the following components in calculating Ignition Control (IC) spark timing:

^ Ignition Control module (ICM).
^ Engine Coolant Temperature (ECT) sensor.
^ Intake Air Temperature (IAT) sensor.
^ Mass Air Flow (MAF) sensor.
^ Trans Range or PNP inputs from Trans Range switch or Park/Neutral Position switch.
^ Throttle Position (TP) sensor.
^ Vehicle Speed Sensor (VSS) / Trans Output Speed Sensor (TOSS).

Input Components
Input components are monitored for circuit continuity and out-of-range values. This includes rationality checking. Rationality checking refers to indicating a fault when the signal from a sensor does not seem reasonable (i.e. a Throttle Position (TP) sensor that indicates high throttle position at low engine loads or MAP voltage). Input components may include, but are not limited to the following sensors:

^ Vehicle Speed Sensor (VSS)
^ Crankshaft Position (CKP) sensor
^ Knock Sensor (KS)
^ Throttle Position (TP) sensor
^ Engine Coolant Temperature (ECT) sensor
^ Camshaft Position (CMP) sensor
^ Manifold Absolute Pressure (MAP) sensor
^ Mass Air Flow (MAF) sensor

In addition to the circuit continuity and rationality check, the ECT sensor is monitored for its ability to achieve a steady state temperature to enable closed loop fuel control.


Output Components
Output components are diagnosed for proper response to control module commands. Components where functional monitoring is not feasible will be monitored for circuit continuity and out-of-range values if applicable.

Output components to be monitored include, but are not limited to the following circuits:

^ Idle Air Control (IAC) Motor
^ Control module controlled EVAP Canister Purge Valve
^ Electronic Transaxle controls
^ A/C relay
^ Cooling fan relay
^ VSS output
^ MIL control
^ Cruise control inhibit
^ The Air System Pump