Diagnostic Circuit Check - Vehicle Control Module (VCM) with Manual Trans

On-Board Diagnostic (OBD) System Check:

On-Board Diagnostic (OBD) Circuit:

Circuit Description
The "On-Board Diagnostic (OBD) System Check" is an organized approach to identifying a problem created by a control module system malfunction. It must be the starting point for any driveability complaint diagnosis. this will direct the service technician to the next logical step in diagnosing the complaint. Understanding the chart and using it properly will reduce diagnostic time and prevent the unnecessary replacement of good parts.

Chart Test Description
Number(s) below refer to circled number(s) on the diagnostic chart.

1. When the ignition switch is turned "ON," the Tech 1 should display serial data. This will determine that the VCM is powered up.

2. This step verifies that the engine will start.

3. This step will isolate if the customer complaint is an MIL or driveability problem with no MIL. Refer to "Diagnostic Trouble Code Description" for a list of valid DTCs. Vehicle Control Module (VCM) An invalid DTC may be the result of a faulty scan tool, PROM or VCM.

4. Although the control module is powered up, a symptom could exist because of a system fault.

5. Comparison of actual control system data with the "Typical Tech 1 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.