On-Board Diagnostic (OBD II) System Check

ON-BOARD DIAGNOSTIC (OBD II) SYSTEM CHECK




Circuit Description
The On-Board Diagnostic (OBD II) System Check is the starting point for any driveability complaint diagnosis. Before using this procedure, perform a careful visual/physical check of the powertrain control module (PCM)/engine control module (ECM) and the engine grounds for cleanliness and tightness.
The OBD II System Check is an organized approach to identifying a problem created by an electronic engine control system malfunction.

Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed-through wire insulation or a wire broken inside the insulation. Check for poor connections or a damaged harness. Inspect the PCM/ECM harness and connections for improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

Steps 1 To 11:

Test Description
Numbers below refer to the step number on the Diagnostic Chart:
1. The Malfunction Indicator Lamp (MIL) should be ON steady with the ignition ON and the engine OFF. If not, go to "Diagnostic Aids".
2. Checks the Class 2 data circuit and ensures that the PCM/ECM is able to transmit serial data.
3. This test ensures that the PCM/ECM is capable of controlling the MIL and the MIL driver circuit is not shorted to ground.
4. If the engine will not start, refer to "Engine Cranks But Will Not Run". See Diagnosis By Symptom.
7. A scan tool parameter which is not within the typical range may help to isolate the area which is causing the problem.
10. This vehicle is equipped with a PCM/ECM which utilizes an electrically erasable programmable read only memory (EEPROM). The replacement PCM/ECM must be programmed. Refer to Powertrain Control Module / Service and Repair.