DTC P0641 or P0651. Cadillac XLR 2008

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 2008 🢒 XLR 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 DTC P0641 or P0651

Diagnostic Instructions

•	Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

•	Review Strategy Based Diagnosis for an overview of the diagnostic approach.

•	Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0641: 5-Volt Reference 1 Circuit

DTC P0651: 5-Volt Reference 2 Circuit

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference 1 Circuit	P0107, P0452, P0532, P0641, P1183, P2228	P2127	P0533, P0641, P2229, P2261
Accelerator Pedal Position (APP) Sensor 1 5-Volt Reference 2 Circuit	P0651	P2122	P0651
Air Conditioning (A/C) Refrigerant Pressure Sensor 5-Volt Reference 1 Circuit	P0069, P0107, P0340, P0345, P0365, P0390, P0452, P0522, P0532, P0641¹, P1183, P2228	P0532	P0533, P0641¹, P2229, P2261
Fuel Tank Pressure (FTP) Sensor 5-Volt Reference 1 Circuit	P0069, P0107, P0340, P0345, P0365, P0390, P0452, P0522, P0532, P0641, P1183, P2228	P0452	P0533, P0641¹, P2229, P2261
Manifold Absolute Pressure (MAP) Sensor 5-Volt Reference 1 Circuit	P0107, P0452, P0522, P0532, P0641, P1183, P2228	P0107	P0533, P0641¹, P2229, P2261
Throttle Position (TP) Sensor 1 and 2 5-Volt Reference 2 Circuit	P0651	P0122, P0222	P0651
Engine Oil Pressure (EOP) Sensor 5-Volt Reference 1 Circuit	P0069, P0107, P0340, P0345, P0365, P0390, P0452, P0522, P0532, P0641¹, P1183, P2228	P0522	P0533, P0641¹, P2229, P2261
Supercharger Intake Air Pressure (SIAP) 5-Volt Reference 1 Circuit	P0069, P0107, P0340, P0345, P0365, P0390, P0452, P0522, P0532, P0641, P1183, P2228	P1183	P0533, P0641¹, P2229, P2261
Crankshaft Position (CKP) Sensor 5-Volt Reference 2 Circuit	P0651	P0335	P0651
Camshaft Position (CMP) Sensor Bank 1 Exhaust 5-Volt Reference 1 Circuit	P0069, P0107, P0340, P0345, P0365, P0390, P0452, P0522, P0532, P0641, P1183, P2228	P0365	P0533, P0641¹, P2229, P2261
Camshaft Position (CMP) Sensor Bank 1 Intake 5-Volt Reference 1 Circuit	P0069, P0107, P0340, P0345, P0365, P0390, P0452, P0522, P0532, P0641, P1183, P2228	P0340	P0533, P0641¹, P2229, P2261
Camshaft Position (CMP) Sensor Bank 2 Exhaust 5-Volt Reference 1 Circuit	P0069, P0107, P0340, P0345, P0365, P0390, P0452, P0522, P0532, P0641, P1183, P2228	P0390	P0533, P0641¹, P2229, P2261
Camshaft Position (CMP) Sensor Bank 2 Intake 5-Volt Reference 1 Circuit	P0069, P0107, P0340, P0345, P0365, P0390, P0452, P0522, P0532, P0641, P1183, P2228	P0345	P0533, P0641¹, P2261, P2229
¹Engine crank but does not start

The engine control module (ECM) has 2 internal 5-volt reference busses called 5-volt reference 1 and 5-volt reference 2. Each reference bus provides 5-volt reference circuits for more than one sensor. Therefore, a fault condition on one 5-volt reference circuit will affect the other 5-volt reference circuits connected to that reference bus. The ECM monitors the voltage on the 5-volt reference busses.

The 5-volt reference 1 bus provides 5 volts to the following sensors:

•	The air conditioning (A/C) refrigerant pressure sensor

•	The manifold absolute pressure (MAP) sensor

•	The fuel tank pressure (FTP) sensor

•	The accelerator pedal position (APP) sensor 2

•	The camshaft position (CMP) sensors

•	The Engine Oil Pressure (EOP) sensor

•	The Supercharger Intake Air Pressure (SIAP) sensor

The 5-volt reference 2 bus provides 5 volts to the following sensors:

•	The APP sensor 1

•	The throttle position (TP) sensor 1 and 2

•	The crankshaft position (CKP) sensor

Conditions for Running the DTC

•	DTCs P0601, P0602, P0603, P0604, P0606, P0607, P060D, P062F, P1680 and P2610 are not set.

•	The ignition is ON.

•	The ignition voltage is more than 5.23 volts.

•	DTCs P0641 and P0651 run continuously when the above conditions are met.

Conditions for Setting the DTC

The ECM detects a voltage out of tolerance condition on the 5-volt reference 1 or 2 bus for more than 0.5 second.

Action Taken When the DTC Sets

•	The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

•	The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

•	The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

•	A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

•	A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

•	Clear the MIL and the DTC with a scan tool.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, observe the scan tool 5-volt reference 1 and 2 parameters. The reading should display Circuit OK for a normally operating system.

Circuit/System Testing

Important: Additional DTCs may set when disconnecting components.

Ignition OFF, disconnect the harness connector of all the sensors connected tot he 5-volt reference bus for the applicable DTC. Refer to Circuit/System Description.

Important: A short to voltage on the signal circuit of certain components may cause this DTC to set.

Ignition ON, test for 4.8-5.2 volts between one of the 5-volt reference circuits and ground.

⇒	If less than the specified range, test all of the 5-volt reference circuits for a short to ground. If all circuits test normal, replace the ECM.

⇒	If greater than the specified range, test for a short to voltage on all of the 5-volt reference circuits or the signal circuit for each component associated with the appropriate 5-volt reference bus for a short to voltage. If all circuits test normal, replace the ECM.

Connect each component associated with the appropriate 5-volt reference bus, one at a time, while monitoring the voltage. The voltage should not change more than 1 volt.

⇒	If the voltage display changes more than the specified range when a component is connected, replace the component.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

•	Accelerator Pedal Position Sensor Replacement

•	Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement

•	Fuel Tank Pressure Sensor Replacement

•	Manifold Absolute Pressure Sensor Replacement

•	Throttle Body Assembly Replacement

•	Control Module References for ECM replacement, setup, and programming