Diagnostic Procedure
- 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 .
- Connect scan tool to Data Link Connector (DLC). See COMPONENT LOCATIONS . Start engine. Observe GEN F-TERMINAL parameter in PCM data list. If GEN F-TERMINAL parameter is 5-95 percent, go to next step. If GEN F-TERMINAL parameter is not as specified, problem may be intermittent. Check wiring and connections, see PRELIMINARY INSPECTION .
- 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.
- Test generator field duty cycle signal circuit, generator harness connector "C" (Gray wire), for a short or an open. See WIRING DIAGRAMS . If problem exists, repair circuit as necessary and go to step 8. If no problem exists, go to step 6.
- 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 .
- 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.
- Replace PCM. After replacement, reprogram PCM.
After repair, go to next step.
- 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.