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Home › Saturn › 2003 › L300 › Repair and Diagnosis › Electrical › Charging Systems › Battery, Charging System & Starting System › Diagnostic Tests › DTC P0621: Generator Light L-Terminal Control Circuit › Diagnostic Procedures

Diagnostic Procedures

  1. Did you perform the Engine Electrical Diagnostic System Check? If yes, go to next step. If no, go to DIAGNOSTIC SYSTEM CHECK - ENGINE ELECTRICAL  .
  2. Install scan tool. Operate vehicle within the conditions for running the DTC. Using scan tool, observe the specific DTC Information for DTC P0621 until the test runs. Does the scan tool indicate that DTC P0621 has passed this ignition cycle? If yes, problem is intermittent. If no, go to next step.
  3. Start engine. With scan tool, observe the ignition 1 parameter in the engine controls data list. Command the Generator L-Terminal OFF for 5 seconds and then back ON. Does the scan tool indicate a change in voltage each time the Generator L-Terminal is commanded OFF and ON? If yes, go to step  6 . If no, go to next step.
  4. Turn OFF the ignition. Disconnect the generator harness connector. Start engine. Measure voltage between the generator turn ON signal circuit of the generator harness connector and a good ground. Is the voltage within 4.5-5.5 volt? If yes, go to step  7 . If no, go to next step.
  5. Test the generator turn on signal circuit for a short, high resistance or open. Did you find and correct the condition? If yes, go to step  10 . If no, go to step  8 .
  6. Test the generator battery voltage output circuit for a high resistance or open. Did you find and correct the condition? If yes, go to step  10 . If no, go to TEST A: CHARGING SYSTEM TEST  .
  7. Inspect for poor connections at the harness connector of the generator. Did you find and correct the condition? If yes, go to step  10 . If no, go to TEST A: CHARGING SYSTEM TEST  .
  8. Inspect for poor connections at the harness connector of the ECM/PCM. Did you find and correct the condition? If yes, go to step  10 . If no, go to next step.
  9. Replace ECM/PCM. See appropriate REMOVAL & INSTALLATION article in ENGINE PERFORMANCE. Program ECM/PCM. After replacing ECM/PCM, go to next step.
  10. Review and record the scan tool Fail Records data. Use scan tool in order to clear the DTC. Operate the vehicle within the Conditions for Running DTC P0621. Using scan tool, observe the Specific DTC Information for DTC P0621 until the test runs. Does the scan tool indicate that DTC P0621 failed? If yes, go to step  3 . If no, system is okay.
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