DTC P0641 or P0651. Buick Lucerne 2007

For 1990-2009 cars only

Makes 🢒 Buick 🢒 2007 🢒 Lucerne 🢒 DTC 🢒 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 provide 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

•	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

•	Engine Controls Connector End Views

•	Engine Control Module 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

Scan Tool Data List

Circuit/System Verification

P0641

Observe the 5-volt reference 1 circuit status parameter with a scan tool. The scan tool should display OK.
Engine running, observe the DTC information with a scan tool. DTC P0641 should not set.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

P0651

Observe the 5-volt reference 2 circuit status parameter with a scan tool. The scan tool should display OK.
Engine running, observe the DTC information with a scan tool. DTC P0651 should not set.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

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