Home >> Chevrolet >> 2003 >> Silverado 1500 HD, 4WD >> Repair and Diagnosis >> Engine Performance >> Testing & Diagnosis >> ENGINE CONTROLS - SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L - Flex Fuel & Gasoline >> Diagnostic Tests >> DTC P0641: 5-Volt Reference Circuit Out Of Range >> Conditions For Setting DTC