P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW





For a complete wiring diagram Refer to Section 8W.



Possible Causes
(F855) PRIMARY 5-VOLT SUPPLY SHORTED TO GROUND
SENSOR SHORTED TO GROUND
5-VOLT SENSOR
PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).



Diagnostic Test

1. ACTIVE DTC

Ignition on, engine not running.
With a scan tool, select View DTCs.

NOTE: Improperly installed aftermarket accessories can cause this DTC to set. Check for wiring added by customer.



Is the DTC Active at this time?

Yes


No

2. (F855) PRIMARY 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND



Turn the ignition off.
Disconnect the C2 PCM harness connector.
Disconnect all the Sensors that share the (F855) Primary 5-volt Supply circuit.
Measure the resistance between ground and the (F855) Primary 5-volt Supply circuit in the CKP Sensor harness connector.

Is the resistance below 100 ohms?

Yes


No

3. 5-VOLT SENSOR



Turn the ignition off.
Reconnect all the previously disconnected Sensors except for the CKP Sensor harness connector.
Ignition on, engine not running.
Measure the voltage on the (F855) Primary 5-volt Supply circuit in the CKP Sensor harness connector.

Is the voltage below 4.5 volts?

Yes


No

4. 5-VOLT SENSOR SHORTED TO GROUND



Measure the voltage on the (F855) Primary 5-volt Supply circuit at the CKP Sensor harness connector.

NOTE: You must Turn the Ignition OFF when disconnecting any of the Sensor harness connectors and Turn the Ignition On to check the voltage readings.


While monitoring the voltage, disconnect each Sensor harness connector that shares the (F855) Primary 5-volt Supply circuit, one at a time.

NOTE: Reconnect all the Sensors and clear all trouble codes before continuing.



Does the voltage increase above 4.5 volts when disconnecting any of the remaining Sensors?

Yes


No

5. PCM

NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.


Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.

Were there any problems found?

Yes


No