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Conditions For Clearing DTC

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, 2002 Chevrolet RV Cutaway, and 2002 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
  1. If engine electrical diagnostic system check was performed, go to next step. If engine electrical diagnostic system check was not performed, go to ENGINE ELECTRICAL DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Connect scan tool to Data Link Connector (DLC). Start engine. Observe GEN F-TERMINAL parameter in PCM data list. If GEN F-TERMINAL parameter is 5-95 percent, test for intermittent and poor connections. If GEN F-TERMINAL parameter is not 5-95 percent, go to next step.
  3. Turn ignition switch to RUN position. Using a test light connected to battery positive voltage, repeatedly probe generator field duty cycle signal circuit, generator harness connector "C" (Gray wire), while observing GENERATOR 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 generator field duty cycle signal circuit, generator harness connector "C" (Gray wire), for a short or an open. If open or short is found, repair as necessary and go to step  8 . If open or short is not found, go to step  6 .
  5. Inspect generator harness connector for poor connections. If problem exists, repair circuit as necessary and go to step  8 . If no problem exists, go to TEST A: CHARGING SYSTEM TEST  under SYSTEM TESTS.
  6. Inspect PCM harness connectors for poor connections. If no problem exists, go to next step. If problem exists, repair circuit as necessary and go to step  8
  7. Replace PCM. SeePOWERTRAIN CONTROL MODULE/VEHICLE CONTROL MODULE under REMOVAL & INSTALLATION in BODY CONTROL MODULES - CHEVY EXPRESS & SAVANNA article in COMMUNICATION DEVICES in ACCESSORIES & EQUIPMENT. After repairs are made, go to next step.
  8. Review and record scan tool fail records data. Using scan tool, clear DTCs. Operate vehicle within Fail Records conditions as noted. Using scan tool, observe Specific DTC information for DTC P1638. If an tool indicates DTC P1638 passed this ignition, system is okay. If scan tool indicates DTC P1638 failed this ignition, go to step  2 .
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