P0642

P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW






For a complete wiring diagram refer to: Electrical Diagrams

When Monitored
Ignition on.

Set Condition
When the PCM recognizes the Primary 5-volt Supply circuit voltage is too low. One Trip Fault. ETC light is flashing.

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.

Diagnostic Test
1. ACTIVE DTC





Ignition on, engine not running.
With a scan tool, read 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 >> Go To 2
No >> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
2. (F855) PRIMARY 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND





Turn the ignition off.
Disconnect the PCM harness connectors.
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 >> Repair the short to ground in the (F855) Primary 5-volt Supply circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 3
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 >> Go To 4
No >> Replace the CKP Sensor.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
4. 5-VOLT SENSOR SHORTED TO GROUND





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

CAUTION: 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 >> Replace the Sensor that causes the (F855) Primary 5-volt Supply circuit voltage to increase when disconnected.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 5
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 >> Repair as necessary
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Replace and program the Powertrain Control Module per Service Information.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test