Diagnostic System Check

CIRCUIT DESCRIPTION
The Powertrain On-Board Diagnostic System Check must be the starting point for any driveability complaint diagnosis. Before using this procedure, you should perform a careful visual/physical inspection of the PCM and engine grounds for clean and secure connections. The Powertrain On-Board Diagnostic System Check is an organized approach to identifying a problem created by an electronic engine control system malfunction.

DIAGNOSTIC AIDS
Inspect for the following:

IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

^ Poor terminal connection.
Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Diagrams.
^ Damaged harness.
Inspect the wiring harness for damage. If the harness appears to be OK, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display may indicate the location of the fault. Refer to Wiring Repairs in Diagrams.
^ Inspect the PCM and the engine grounds for clean and secure connections.

If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.

TEST DESCRIPTION

A Powertrain On Board Diagnostic (OBD) System Check:

Number(s) below refer to the step number(s) on the Diagnostic Table:
1. The MIL should be ON steady with the key ON, engine OFF. If not, the No Malfunction Indicator Lamp table should be used to isolate the malfunction.
2. This test ensures that the PCM is capable of transmitting Class 2 serial data to the DLC and that the Class 2 data circuit is not open or shorted. If a problem is encountered and a malfunctioning scan tool is suspected, try the scan tool on another vehicle to verify operation. If a DLC problem exists, the DLC Diagnosis table should be used to diagnose the condition.
3. If the engine will not start, the Engine Cranks But Will Not Run table should be used to diagnose the condition.
4. The scan tool may display DTCs which are diagnosed in Automatic Transmission/Transaxle Diagnosis. If multiple DTCs are stored, diagnose each DTC according to the following priority:
^ PCM Error DTCs.
^ System Voltage DTCs.
^ Component Level DTCs (Switches, sensor range/performance, sensor high voltage, sensor low voltage, ODMs, etc.).
^ System level DTCs (Fuel trim, Misfire, EGR flow, TWC System, Idle Control System, HO2S Response or HO2S Transition Time Ratio).
5. A scan tool parameter which is not within the typical range may help to isolate the area which is causing the problem.