DTC P0641 or P0651. Buick Lucerne 2009

For 1990-2009 cars only

Makes 🢒 Buick 🢒 2009 🢒 Lucerne 🢒 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	P2127	P0533, P0641
Accelerator Pedal Position (APP) Sensor 1 5-Volt Reference 2 Circuit	P0335, P0651, P2135,	P2122	P0335, P0651, P2135
Air Conditioning (A/C) Refrigerant Pressure Sensor 5-Volt Reference 1 Circuit	P0107, P0452, P0532, P0641	P0532	P0533, P0641
Fuel Tank Pressure (FTP) Sensor 5-Volt Reference 1 Circuit	P0641	P0452	P0533, P0641
Manifold Absolute Pressure (MAP) Sensor 5-Volt Reference 1 Circuit	P0107, P0532, P0641	P0107	P0533, P0641
Throttle Position (TP) Sensor 1 and 2 5-Volt Reference 2 Circuit	P0335, P0651, P2135,	P0122, P0222	P0651, P2135
Secondary Air Injection (AIR) Solenoid 5-Volt Reference 2 Circuit	P0335, P0651, P2135,	P2432	P0335, P0651, P2135,
Crankshaft Position (CKP) Sensor 5-Volt Reference 2 Circuit	P0335, P0651, P2135,	P0335	P0335, P0651, P2135,
Camshaft Position (CMP) Sensor 5-Volt Reference 1 Circuit	P0107, P0532, P0641	P0340	P0533, P0641
Exhaust Gas Recirculation (EGR) position sensor 5-Volt Reference 1 Circuit	P0107, P0452, P0641	P0405	P0641

The control module 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 control module 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 exhaust gas recirculation (EGR) position sensor

•	The camshaft position (CMP) 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 secondary air injection (AIR) Solenoid

•	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 control module 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

DTCs P0641 and P0651 are Type A DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0641 and P0651 are Type A DTCs.

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

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

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

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

•	Exhaust Gas Recirculation Valve Replacement

•	Fuel Tank Pressure Sensor Replacement

•	Manifold Absolute Pressure Sensor Replacement

•	Throttle Body Assembly Replacement