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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> Electrical >> Charging Systems >> Charging System >> Diagnostic Tests >> DTC P1638: Out Of Range Duty Cycle Signal >> Diagnostic Procedure

Diagnostic Procedure

  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 engine. Using scan tool, observe GEN F-Terminal parameter in Powertrain Control Module (PCM) data list. If scan tool indicates GEN F-Terminal parameter is 5-95 percent, problem is intermittent. Check wiring and connections. If scan tool does not indicate GEN F-Terminal is 5-95 percent, go to next step.
  3. Turn ignition switch to RUN position. Connect test light to battery positive voltage. Repeatedly probe generator harness connector terminal "C" (Gray wire), while observing Generator Pulse Width Modulated (PWM) on scan tool. If Generator PWM display is affected, go to step  5. If Generator PWM display is not affected, go to next step.
  4. Test Gray wire for a short or an open between generator harness connector terminal "C" and PCM harness connector. See WIRING DIAGRAMS . If problem exists, repair circuit as necessary. After repair, go to step  8. If problem does not exist, go to step  6.
  5. Inspect generator harness connector for poor connections. If problem exists, repair as necessary. After repair, go to step  8. If problem does not exist, perform TEST A: CHARGING SYSTEM TEST  under SYSTEM TESTS.
  6. Inspect PCM harness connector for poor connections. If problem exists, repair as necessary. After repair, go to step  8. If problem does not exist, go to next step.
  7. Replace PCM. See REMOVAL & INSTALLATION article in ENGINE PERFORMANCE. Program PCM. After repair, go to next step.
  8. Review and record scan tool Fail Records data. Using scan tool, clear DTC's. Operate vehicle under conditions noted in Fail Records. Check for DTC. If DTC P1638 resets, repeat test beginning at step  2. If DTC P1638 does not reset, system is okay.
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