The engine control module (ECM) has 2 internal 5-volt reference circuits called 5-volt reference 1 and 5-volt reference 2. Each reference circuit 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 circuit. The ECM monitors the voltage on the 5-volt reference circuits.

The ECM detects a voltage out of tolerance condition on the 5-volt reference 1 or 2 circuit for more than 0.5 second.

DTCs P0641 and P0651 are Type A DTCs.

DTCs P0641 and P0651 are Type A DTCs.

The 5-volt reference 1 circuit provides 5 volts to the following sensors:

The 5-volt reference 2 circuit provides 5 volts to the following sensors:

It may be possible to locate the fault by disconnecting one component at a time from the affected 5-volt reference circuit while viewing the 5-Volt Reference circuit status parameter on the scan tool. The scan tool parameter will change from Fault to OK when the source of the fault is disconnected. If all 5-volt reference components have been disconnected and a fault is still indicated, the fault may exist in the wiring harness.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the scan tool 5-volt reference 1 and 2 parameters. The reading should display Circuit OK for a normally operating system.

Important: A short to voltage on the signal circuit of certain components may cause this DTC to set.

1. Ignition OFF, disconnect the harness connector of all appropriate sensors for the applicable DTC. Refer to Diagnostic Aids for appropriate sensors.
2. Ignition ON, measure for 4.8-5.2 volts between one of the 5-volt reference circuits and ground.

⇒	If less than the specified range, test for a short to ground on all the 5-volt reference circuits. 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. If all circuits test normal, replace the ECM.

3. Connect each component associated with the 5-volt reference circuit, one at a time, while monitoring the voltage. Verify the voltage remains between 4.8-5.2 volts.

⇒	If not within the specified range when a component is connected, test the signal circuit for a short to voltage. If the circuit tests normal, replace the appropriate component.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.