DTC P0641 or P0651. Cadillac STS 2007

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 2007 🢒 STS 🢒 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 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, P0641, P1183, P2228, P0532, P0452	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	¹P0641, P0107, P0452, P0532, P1183, P2228, P0069, P0522, P0390, P0365, P0345, P0340	P0532	¹P0641, P2261, P2229, P0533
Fuel Tank Pressure (FTP) Sensor 5-Volt Reference 1 Circuit	P0641, P0107, P0452, P0532, P1183, P2228, P0069, P0522, P0390, P0365, P0345, P0340	P0452	¹P0641, P2261, P2229, P0533
Manifold Absolute Pressure (MAP) Sensor 5-Volt Reference 1 Circuit	P0641, P1183, P2228, P0532, P0452, P0107, P0522	P0107	¹P0641, P2261, P2229, P0533
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	¹P0641, P0107, P0452, P0532, P1183, P2228, P0069, P0522, P0390, P0365, P0345, P0340	P0522	¹P0641, P2261, P2229, P0533
Supercharger Intake Air Pressure (SIAP) 5-Volt Reference 1 Circuit	P0641, P0107, P0452, P0532, P1183, P2228, P0069, P0522, P0390, P0365, P0345, P0340	P1183	¹P0641, P2261, P2229, P0533
Crankshaft Position (CKP) Sensor 5-Volt Reference 2 Circuit	P0651	P0335	P0651
Camshaft Position (CMP) Sensor Bank 1 Exhaust 5-Volt Reference 1 Circuit	P0641, P0107, P0452, P0532, P1183, P2228, P0069, P0522, P0390, P0365, P0345, P0340	P0365	¹P0641, P2261, P2229, P0533
Camshaft Position (CMP) Sensor Bank 1 Intake 5-Volt Reference 1 Circuit	P0641, P0107, P0452, P0532, P1183, P2228, P0069, P0522, P0390, P0365, P0345, P0340	P0340	¹P0641, P2261, P2229, P0533
Camshaft Position (CMP) Sensor Bank 2 Exhaust 5-Volt Reference 1 Circuit	P0641, P0107, P0452, P0532, P1183, P2228, P0069, P0522, P0390, P0365, P0345, P0340	P0390	¹P0641, P2261, P2229, P0533
Camshaft Position (CMP) Sensor Bank 2 Intake 5-Volt Reference 1 Circuit	P0641, P0107, P0452, P0532, P1183, P2228, P0069, P0522, P0390, P0365, P0345, P0340	P0345	¹P0641, P2261, P2229, P0533
¹Engine crank but does not start

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 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 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 Control Module Connector End Views

•	Engine Controls Connector End Views

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

Scan Tool Reference

Scan Tool Data List

Circuit/System Verification

P0641

Observe the MAP sensor voltage parameter with a scan tool with the ignition ON and the engine OFF. The scan tool should display approximately 2.2 volts for a normally operating system.
Engine running, observe the DTC information with a scan tool. DTCs P0641 or 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.

P0651

With the ignition ON and the engine OFF, observe the APP sensor 1 voltage parameter with a scan tool. The scan tool should display approximately 0.96 volt for a normally operating system.
Engine running, observe the DTC information with a scan tool. DTCs P0641 or 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

•	Fuel Tank Pressure Sensor Replacement

•	Manifold Absolute Pressure Sensor Replacement

•	Throttle Body Assembly Replacement