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 MANUALSCHEVROLET2006CHEVY EXPRESS G2500, VAN CARGO, 6.6 2REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 201 (CHARGING SYSTEM)DIAGNOSTIC TESTSDTC P1638: PULSE WIDTH MODULATION SIGNAL OUT OF RANGEDIAGNOSTIC PROCEDURE
2006 Chevrolet Chevy Express G2500, Van Cargo, 6.6 2
Diagnostic Procedure
2006 Chevrolet Chevy Express G2500, Van Cargo, 6.6 2SECTION Diagnostic Procedure
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
- 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.
- Connect scan tool to Data Link Connector (DLC). DLC is located below left side of instrument panel. Start engine. 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 parameter is 5-95 percent, go to next step.
- 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 Generator Pulse Width Modulation (PWM) on scan tool. If Generator PWM display is affected, go to step 8 . If Generator PWM display is not affected, go to next step.
- Test Gray wire for a short or an open between generator harness connector terminal "C" and 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 .
- 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.
- Inspect PCM harness connectors for poor connections. If problem exists, repair as necessary. After repair, go to step 8 . If problem does not exist, go to next step.
- Replace PCM. If equipped with a 6.6L (Diesel), replace ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article in ENGINE PERFORMANCE. Program PCM/ECM. After repair, go to next step.
- Review and record scan tool Fail Records data. Using scan tool, clear DTC's. 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 an tool indicates DTC P1638 passed this ignition, system is okay.
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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.