DTC P0642 from the WH Service manual
P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW (CONTINUED)
For the Engine circuit diagram (Refer to 9 - ENGINE - SCHEMATICS AND DIAGRAMS).
For a complete wiring diagram Refer to Section 8W.
² When Monitored:
Ignition on.
² 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. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).
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 the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
9 - 718 ENGINE ELECTRICAL DIAGNOSTICS WK
P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW (CONTINUED)
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 >> Repair the short to ground in the (F855) Primary 5-volt
Supply circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer
to 9 - ENGINE - STANDARD PROCEDURE)
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 the POWERTRAIN VERIFICATION TEST. (Refer
to 9 - ENGINE - STANDARD PROCEDURE)
WK ENGINE ELECTRICAL DIAGNOSTICS 9 - 719
P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW (CONTINUED)
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 the POWERTRAIN VERIFICATION TEST. (Refer
to 9 - ENGINE - STANDARD PROCEDURE)
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 the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No >> Replace and program the Powertrain Control Module per Service Information.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
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