P0641 Diagnostic and Limp Mode Issue on 2003 GMC Sierra 2500HD Duramax Diesel
I own a 2003 GMC Sierra 2500HD with a 6.6L Duramax diesel engine, and I'm currently experiencing a P0641 diagnostic code, which has triggered the vehicle's limp mode. The issue is affecting engine performance and limiting functionality. I need help identifying possible causes and troubleshooting steps to resolve this fault code.
Are there any additional diagnostic trouble codes present? Any other symptoms such as rough idling, poor acceleration, or engine stalling? A problem may exist in the reference voltage circuit supplied by the Powertrain Control Module (PCM) bus to key sensors including Accelerator Pedal Position (APP1), APP3, Engine Oil Pressure (EOP), and Fuel Rail Pressure (FPR). These sensors rely on a shared 5V reference signal from the PCM. If one of these circuits is shorted to ground or shows abnormal voltage, it can trigger P0641. First point of investigation: any aftermarket modifications or sensor upgrades? Can you access wiring diagrams and use a digital multimeter (DVOM) to verify reference voltages at the sensors? *Note: 'Bus' refers to the shared 5V power source used by all these sensors from the PCM.