- Powertrain/On-Board Diagnostic System Check

Diagnostic Chart:

Electrical:

CIRCUIT DESCRIPTION

The On-Board Diagnostic (OBD) System Check is an organized approach to identifying a problem created by a control module system malfunction. The OBD is the starting point for any driveability concern diagnosis. The OBD directs the service technician to the next logical step in diagnosing the concern. Perform this check ONLY if there is a driveability complaint or if you have been sent to this system check from another section in the service information.

Understanding the table properly reduces the diagnostic time. Proper use of the OBD helps prevent the unnecessary replacement of good parts.


DIAGNOSTIC AIDS

IMPORTANT: Do not clear the DTCs unless directed by a diagnostic procedure. Clearing the DTCs will also clear valuable Freeze Frame and Failure Records data.

Inspect all related wiring and connections including the connections at the VCM. These may cause an intermittent malfunction.

Check any circuitry that is suspected of causing an intermittent problem for the following conditions:

^ Backed out terminals

^ Improper mating

^ Broken locks

^ Improperly formed or damaged terminals

^ Poor terminal to wiring connections

^ Physical damage to the wiring harness Corrosion

TEST DESCRIPTION

The numbers below refer to the step numbers in the diagnostic table.

1. This step isolates if the customer complaint is a MIL or a driveability problem with no MIL.

2. When the ignition switch is turned ON, the scan tool should display serial data. This step determines if the VCM is powered up.

3. Refer to DTC Identification for a list of valid DTCs. A faulty scan tool, VCM Programming or VCM may result in an invalid DTC.

4. This step verifies that the engine will start.

5. Comparison of an actual control system data with the Typical Scan Tool Data Values is a quick check to determine if any parameter is not within limits. A base engine problem (i.e., advanced cam timing may substantially alter sensor values).