Diagnostic Circuit Check - With Diagnostic Scan Tool

Diagnostic Circuit Check:

Diagnostic Circuit:

Circuit Description:
The diagnostic circuit check is an organized approach to identifying a problem created by a Computer Command Control System malfunction. It must be the starting point for any driveability complaint diagnosis, because it directs the service technician to the next logical step in diagnosing the complaint. Understanding the chart and using it correctly will reduce diagnostic time and prevent the unnecessary replacement of good parts.

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

1. This step is a check for the proper operation of the "Service engine Soon" light. The "SES" light should be "ON" steady.

2. No "SES" light at this point indicates that there is a problem with the "SES" light circuit or the ECM/PCM control of that circuit.

3. This test cheeks the ability of the ECM/PCM to control the "SES" light. With the diagnostic terminal grounded, the "SES" light should flash a Code 12 three times, followed by any trouble code stored in memory. Depending upon the type of ECM/PCM, PROM or MEM-CAL error may result in the inability to flash Code 12.

4. This test check "Quad-Driver" circuit. If the "SES" light flashes less than three times, indicates that there is a problem with the "SES" light circuit or the ECM/PCM control of that circuit. See PCM QDR Check Procedure, if applicable.

5. Use Tech 1 to aid diagnosis, therefore, serial data must be available. If a PROM or MEM-CAL error is present, the ECM/PCM may have been able to flash Code 12/51, but not enable serial data.

6. Although the ECM is powered up, a "Cranks But Will Not Run" symptom could exist because of an ECM/PCM or system problem.

7. This step will isolate if the customer complaint is a "SES" light or a driveability problem with no "SES" light. Refer to "Diagnostic Code Identification" for a list of valid codes. An invalid code may be the result of a faulty "Scan" tool, MEM-CAL/PROM or ECM/PCM.

8. 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. Keep in mind that a base engine problem (i.e. advanced cam timing) may substantially alter sensor values.

9. Installation of a Tech 1 "Scan" tool will provide a good ground path for the ECM/PCM and may hide a driveability complaint due to poor ECM/PCM grounds. Testing and Inspection

10. If the actual data is not within the typical values established, refer to the applicable diagnosis section to provide a functional check for the suspect component or system.