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 5-volt reference 2 bus provides 5 volts to the air conditioning (A/C) refrigerant pressure sensor

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.

DTCs P0641 and P0651 are Type A DTCs.

DTCs P0641 and P0651 are Type A DTCs.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

P0641

Observe the MAP sensor voltage parameter with a scan tool with the ignition ON and the engine OFF. The scan tool should display 3.6-4.8 volts for a normally operating system.

P0651

With the ignition ON and the engine OFF, observe the A/C Refrigerant Pressure-A/C High Side Pressure parameter with a scan tool. The scan tool should display 0.2-4.9 volt or 9-453 psi for a normally operating system.

P0641

1. With the ignition OFF, disconnect the harness connector at the MAP sensor.
2. With the ignition ON, measure for 4.8-5.2 volts between the MAP sensor 5-volt reference circuit and ground.
3. Command the EGR valve to 100 percent while monitoring the MAP sensor 5-volt reference circuit with a DMM.

⇒	If within 4.8-5.2 volts, refer to Testing for Intermittent Conditions and Poor Connections.

4. With the ignition OFF, disconnect the harness connector at the EGR valve.
5. With the ignition ON, measure EGR valve 5-volt reference circuit.

⇒	If within 4.8-5.2 volts, replace the EGR valve.

⇒	If over 5.2 volts, check for unexpected voltage at each 5-volt reference circuit or the signal circuit for each component associated with the 5-volt reference.

⇒	If under 4.8 volts, check for a short to ground or low reference circuit at each 5-volt reference circuit.

6. With the ignition ON, use a scan tool to observe the voltage parameter for each component associated with the 5-volt reference circuit while disconnecting each component one at a time.

⇒	If the data parameters change with any component being disconnected, replace the component.

7. If all circuits tested are normal, replace the control module.

P0651

1. With the ignition OFF, disconnect the harness connector at the A/C pressure sensor.
2. With the ignition ON, measure for 4.8-5.2 volts between the A/C pressure sensor 5-volt reference circuit and ground.

⇒	If within 4.8-5.2 volts, refer to Testing for Intermittent Conditions and Poor Connections.

⇒	If over 5.2 volts, test all 5-volt references circuits for a short to voltage. If all circuits tested are normal, replace the A/C pressure sensor.

⇒	If under 4.8 volts, turn OFF the ignition and test all 5-volt references circuits for a short to ground or any sensor low reference circuit.

3. If all circuits tested are normal, replace the control module.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.