Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2006SUBURBAN C2500, 6.0 UREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 199 (CHARGING SYSTEM)DIAGNOSTIC TESTSDTC P1638: PULSE WIDTH MODULATED SIGNAL OUT OF RANGEDIAGNOSTIC PROCEDURE
2006 Chevrolet Suburban C2500, 6.0 U
Diagnostic Procedure
2006 Chevrolet Suburban C2500, 6.0 USECTION Diagnostic Procedure
WARNING: This page is about a different car, the 2003 GMC Savana Special, 2003 GMC Savana Camper Special, 2003 GMC Savana, and 2003 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
- 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.
- 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.
- 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. 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.
- 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.
- 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. See appropriate REMOVAL & INSTALLATION article in ENGINE PERFORMANCE. Program 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.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.