On-Board Diagnostics: Notes

WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: For more information on PCM operation, see THEORY & OPERATION - 1.8L VIBE article.

The Powertrain Control Module (PCM) diagnoses any troubles which may occur in the engine control system when the ignition switch is in the ON position with the engine running. The PCM indicates a malfunction by illuminating the Malfunction Indicator Light (MIL) when a fault occurs in any of the following systems:

Heated Oxygen Sensor 1 (HO2S 1)
Heated Oxygen Sensor 2 (HO2S 2)
Engine Coolant Temperature (ECT) Sensor
Throttle Position (TP) Sensor (Including CTP Switch)
Vehicle Speed Sensor (VSS)
Intake Air Temperature (IAT) Sensor
Mass Air Flow (MAF) Sensor
Camshaft Position (CMP) Sensor
Crankshaft Position (CKP) Sensor
Knock Sensor (KS) System
Evaporative Emission (EVAP) Control System
Idle Air Control (IAC) System
CMP Actuator Solenoid System
Rocker Arm Oil Control system
Misfire Detection
Fuel-Trim
Catalyst Monitor
Central Processing Unit (CPU) Of The PCM

When PCM detects a malfunction in one of the above areas, PCM will illuminate or flash the MIL to notify driver of the occurrence of a fault. PCM will store a DTC when PCM illuminates the MIL. PCM will turn OFF the MIL after 3 consecutive ignition cycles without the malfunction occurring. DTC will remain stored in the PCM memory after the MIL is OFF.