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Home >> Cadillac >> 2007 >> Escalade EXT >> Repair and Diagnosis >> External Pages >> Different car >> Section 202 (Charging System) >> Diagnostic Tests >> DTC P1638: Pulse Width Modulation Signal Out Of Range >> Diagnostic Procedure
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Diagnostic Procedure

WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
  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 information for DTC P1638 in Engine Controls. If scan tool indicates DTC P1638 passed this ignition, problem is intermittent. Check wiring and connections. If scan tool indicates DTC P1638 failed this ignition, go to next step.
  3. Turn ignition switch to OFF position. Disconnect generator harness connector. Turn ignition switch to RUN position. Connect a test light to battery positive voltage. Repeatedly probe generator harness connector terminal "C" (Gray wire), while observing GEN F-Terminal Signal on scan tool. If Generator Pulse Width Modulation (PWM) display is affected, go to step  5 . If Generator PWM Signal 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 Powertrain Control Module (PCM) harness connector C2 terminal No. 52. See WIRING DIAGRAMS  . If problem exists, repair 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 appropriate REMOVAL, OVERHAUL & INSTALLATION - CORVETTE 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 DTCs. Operate vehicle within Fail Records conditions as noted. Using scan tool, observe Specific DTC information for DTC P1638. If scan tool indicates DTC P1638 failed this ignition, repeat test beginning at step  2 . If scan tool indicates DTC P1638 passed this ignition, system is okay.
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