Test Description
This information is used while reading the diagnostic chart. The numbers below refer to the circled numbers found on the diagnostic chart.
- This step is a check for the proper operation of the "Service Engine Soon" light. The "SES" light should be ON steady.
- No "SES" light at this point indicates that there is a problem with the "SES" light circuit or the ECM control of that circuit.
- This test checks the ability of the ECM 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, a PROM or MEM-CAL error may result in the inability to flash Code 12.
- Most procedures and DTCs use a scan tool to aid diagnosis, therefore, serial data must be available. If a PROM or MEM-CAL error is present the ECM may have been able to flash Code 12/51, but not enable serial data.
- Although the ECM is powered up, a "Cranks But Will Not Run" symptom could exist because of an ECM or system problem.
- This step will isolate if the customer complaint is a "SES" light or a driveability problem with no "SES" light. Refer to DIAGNOSTIC TROUBLE CODE IDENTIFICATION/AVAILABILITY in this article for a list of valid codes. An invalid code may be the result of a faulty scan tool, MEM-CAL/PROM or ECM/PCM.
- Comparison of actual control system data with the typical 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.
- Installation of a scan tool will provide a good ground path for the ECM and may hide a driveability complaint due to poor ECM grounds.
- If the actual data is not within the typical values established, a fault in a component or system has been identified. Troubleshoot as necessary.