Initial Inspection and Diagnostic Overview

On-Board Diagnostic (OBD) System Check:

On-Board Diagnostic (OBD) Wiring Schematic:

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 cycled to "ON," the Malfunction Indicator Lamp (MIL) should turn "ON" briefly, then "OFF" briefly, then remain "ON" steady. This sequence will determine that the vehicle diagnostics are operational.
2. This step will isolate if the customer complaint is a MIL or driveability problem.
3. Although the control module is powered up, a symptom could exist because of a system fault.
4. Use Tech 1 scan tool to aid diagnosis, therefore, serial data must be available. If a Programmable Read Only Memory (PROM) (MEM-CAL) error is present, the PCM may have been able to flash Diagnostic Trouble Code (DTC) 12/51, but not enable serial data.
5. This step will isolate if the customer complaint is a MIL or driveability problem with no MIL. Refer to "Diagnostic Trouble Code Identification" in this section for a list of valid DTCs. An invalid DTC may be the result of a faulty scan tool, PROM or PCM.
6. Although the PCM is powered up, a "Cranks But Will Not Run" symptom could exist because of a PCM or system problem.
7. 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).

NOTE: The PCM utilizes a 24 pin "Pink" connector, a 32 pin "Pink" connector and a 32 pin "Blue" connector. The 24 pin "Pink" connector is labeled "A" and "B", the 32 pin "Pink" connector is labeled "C" and "D" and the 32 pin "Blue" connector is labeled "C" and "D". When referencing PCM connector pin outs, the "Blue" PCM connector will be referred to as the "E" and "E" connector.