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Diagnostic Procedure

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  1. If diagnostic system check was not performed, perform ENGINE ELECTRICAL DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. If diagnostic system check was performed, go to next step.
  2. Connect scan tool to Data Link Connector (DLC). DLC is located below left side of instrument panel. Start and idle engine. Using scan tool, observe Generator L-Terminal parameter. If scan tool displays Inactive, go to next step. If scan tool does not display Inactive, go to step  4.
  3. Connect a test light between ground, and backprobe generator feed circuit (Red wire). If test light illuminates, go to next step. If test light does not illuminate, problem is intermittent. Check wiring and connections.
  4. Inspect generator harness connector for poor connections. If problem does not exist, go to next step. If problem exists, repair as necessary. After repair, go to step  11.
  5. Turn ignition switch to OFF position. Disconnect Powertrain Control Module (PCM) connector C2. PCM is located at right front of engine compartment. Test Red wire for an open or high resistance between generator harness connector terminal "B" and PCM harness connector. See WIRING DIAGRAMS . If continuity exists, go to next step. If continuity does not exist, go to step  8.
  6. Test Red wire for an open or high resistance between generator connector terminal "B" and battery ground. If continuity exists, go to next step. If continuity does not exist, go to step  9.
  7. Inspect PCM harness connector for poor connections. If problem exists, repair as necessary. After repair, go to step  13. If problem does not exist, go to step  9.
  8. Repair open or high resistance in generator circuit. See WIRING DIAGRAMS . After repair, go to step  13.
  9. Repair short to ground in generator circuit. See WIRING DIAGRAMS . After repair, go to step  13.
  10. Replace PCM. See REMOVAL & INSTALLATION article in ENGINE PERFORMANCE. Program PCM. After repair, go to step  13.
  11. Disconnect generator harness connector. Start engine. Measure voltage between ground and generator connector terminal "B" (Red wire). If voltage is equal to or greater than 10 volts, go to step  13. If voltage is not equal to or greater than 10 volts, go to next step.
  12. Replace generator. See GENERATOR  under REMOVAL & INSTALLATION. After repair, go to step  13.
  13. Using scan tool, clear DTC's. Start engine and run at 1000 RPM. Check for DTC. If DTC P0621 resets, repeat test beginning at step  2. If DTC P0621 does not reset, system is okay.
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