P0641-SENSOR REFERENCE VOLTAGE 1 CIRCUIT

For a complete wiring diagram, refer to the Wiring Information.

Theory of Operation

The Powertrain Control Module (PCM) contains 3 internal 5-Volt Sensor Supply sources. Each 5-Volt Supply source is split into parallel circuits to provide 5 volts to multiple sensors. Sensor Supply 1 provides 5 volts to the Mass Air Flow (MAF) Sensor, EGR Position Sensor and the Differential Pressure Sensor. The EGR system is disabled when the fault code is active.

When Monitored:
With the ignition on.
Set Condition:
The PCM detects low voltage on the Sensor Supply 1 circuit for 0.10 second.

Possible Causes
5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
MASS AIR FLOW SENSOR
EGR POSITION SENSOR
DIFFERENTIAL PRESSURE SENSOR
POWERTRAIN CONTROL MODULE (PCM)

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

1. CHECK FOR ACTIVE DTC

1.	Turn the ignition on.

2.	With the scan tool, View DTCs.

Is the status Active for this DTC?

Yes

Go To 2

Perform the INTERMITTENT DTC diagnostic procedure. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

2. MASS AIR FLOW SENSOR

1.	Turn the ignition off.

2.	Disconnect the MAF Sensor harness connector.

3.	Turn the ignition on.

4.	Measure the voltage of the (F888) MAF Sensor 5-Volt Supply circuit.

Is the voltage above 4.75 volts?

Yes

Replace the MAF Sensor in accordance with the service information.
Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

Go To 3

3. EXHAUST DIFFERENTIAL PRESSURE SENSOR

1.	Turn the ignition off.

2.	Disconnect the Exhaust Differential Pressure Sensor harness connector.

3.	Turn the ignition on.

4.	Measure the voltage of the (K354) Exhaust Differential Pressure Sensor 5-Volt Supply circuit.

Is the voltage above 4.75 volts?

Yes

Replace the Exhaust Differential Pressure Sensor in accordance with the service information.
Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

Go To 4

4. EGR POSITION SENSOR

1.	Turn the ignition off.

2.	Disconnect the EGR Valve Assembly harness connector.

3.	Turn the ignition on.

4.	Measure the voltage of the (K35) EGR Position Sensor 5-Volt Supply circuit at the EGR Valve Assembly harness connector.

Is the voltage above 4.75 volts?

Yes

Replace the Camshaft Position Sensor in accordance with the service information.
Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

Go To 5

5. CHECK THE 5-VOLT SUPPLY CIRCUIT FOR A SHORT TO GROUND

1.	Turn the ignition off.

2.	Disconnect the PCM harness connectors.

3.	Measure the resistance between ground and the (K354) Exhaust Differential Pressure Sensor 5-Volt Supply circuit at the Exhaust Differential Pressure Sensor harness connector.

4.	Measure the resistance between ground and the (K35) EGR Position Sensor 5-Volt Supply circuit at the EGR Valve Assembly harness connector.

5.	Measure the resistance between ground and the (F888) MAF Sensor 5-Volt Supply circuit at the MAF Sensor harness connector.

Is the resistance above 10k Ohms for each circuit?

Yes

Go To 6

Repair the 5-Volt Supply circuit that measured below 10k Ohms for a short to ground.
Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

6. POWERTRAIN CONTROL MODULE

1.	Inspect the (K35) EGR Position Sensor 5-Volt Supply circuit between the EGR Valve Assembly harness connector and the PCM harness connector.

2.	Inspect the (K354) Exhaust Differential Pressure Sensor 5-Volt Supply circuit between the Exhaust Differential Pressure Sensor harness connector and the PCM harness connector.

3.	Inspect the (F888) MAF Sensor 5-Volt Supply circuit between the MAF Sensor harness connector and the PCM harness connector.

4.	Look for any chafed, pierced, pinched, or partially broken wires.

5.	Look for broken, bent, pushed out or corroded terminals.

6.	Perform any Technical Service Bulletins that may apply.

Were any problems found?

Yes

Repair as necessary.
Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

Replace the Powertrain Control Module in accordance with the service information.
Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

P0641-SENSOR REFERENCE VOLTAGE 1 CIRCUIT

Theory of Operation

Possible Causes