Diesel

P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW





For a complete wiring diagram Consult Diagrams/Electrical

- When Monitored:
With the ignition on.

- Set Condition:
The ECM detects low voltage on the Sensor Supply #1 circuit for 0.10 seconds.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.Initial Inspection and Diagnostic Overview

Theory of Operation

The ECM 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 Camshaft Position Sensor and the Accelerator Pedal Position Sensor #1.

Diagnostic Test

1. CHECK FOR ACTIVE DTC
Turn the ignition on.
With the scan tool, erase ECM DTCs.
With the scan tool, View DTCs.
Is the status Active for this DTC?

Yes

- Go To2

No

- Refer to the *CHECKING FOR AN INTERMITTENT DTC Diagnostic Procedure.Intermittent Condition

2. CAMSHAFT POSITION SENSOR




Turn the ignition off.
Disconnect the CMP Sensor harness connector.
Turn the ignition on.
Measure the voltage of the (K844) Camshaft Position Sensor 5 Volt Supply circuit in the CMP Sensor harness connector.
Is the voltage above 4.6 volts?

Yes

- Replace the Camshaft Position Sensor.
- Perform the ECM Verification Test.Verification Tests

No

- Go To3

3. ACCELERATOR PEDAL POSITION SENSOR




Turn the ignition off.
Disconnect the APP Sensor harness connector.
Turn the ignition on.
Measure the voltage of the (F855) Accelerator Pedal Position Sensor No. 1 5 Volt Supply circuit in the APP Sensor harness connector.
Is the voltage above 4.6 volts?

Yes

- Replace the Accelerator Pedal Position Sensor.
- Perform the ECM Verification Test.Verification Tests

No

- Go To4

4. 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND




Turn the ignition off.
Disconnect the ECM harness connectors.
Measure the resistance between ground and the (F855) Accelerator Pedal Position Sensor No. 1 5 Volt Supply circuit in the APP Sensor harness connector.
Measure the resistance between ground and the (K844) Camshaft Position Sensor 5 Volt Supply circuit in the CMP harness connector.
Is the resistance above 1000 ohms for both circuits?

Yes

- Go To5

No

- Repair the 5 Volt Supply circuit for a short to ground.
- Perform the ECM Verification Test.Verification Tests

5. ENGINE CONTROL MODULE (ECM)
Inspect the (K844) Camshaft Position Sensor 5 Volt Supply circuit between the CMP harness connector and the ECM harness connector.
Inspect the (F855) Accelerator Pedal Position Sensor No. 1 5 Volt Supply circuit between the APP Sensor harness connector and the ECM harness connector
Look for any chafed, pierced, pinched, or partially broken wires.
Look for broken, bent, pushed out or corroded terminals.
Monitor the scan tool data relative to this circuit and wiggle test the wiring and connectors.
Look for the data to change or for the DTC to reset during the wiggle test.
Search for any Technical Service Bulletins that may apply.
Were any problems found?

Yes

- Repair as necessary.
- Perform the ECM Verification Test. Verification Tests.

No

- Replace the ECM.
- Perform the ECM Verification Test. Verification Tests.