Powertrain Control Module (PCM)

P0643-SENSOR REFERENCE VOLTAGE 1 CIRCUIT HIGH

For a complete wiring diagram, refer to the Wiring Information.

Theory of Operation

The Powertrain Control Module (PCM) contains two internal 5-Volt Sensor Supply sources. Each 5-Volt Supply source is split into parallel circuits to provide a 5.0 volt reference to multiple three wire sensors.

- When Monitored:
With the ignition on.

- Set Condition:
When the Powertrain Control Module (PCM) recognizes the Primary 5-Volt Supply circuit voltage is too high. One Trip Fault. ETC light is flashing. If the vehicle is equipped with the stop/start feature, the system will be disabled when this DTC is active.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

Diagnostic Test

1. ACTIVE DTC

NOTE: Improperly installed aftermarket accessories can cause this DTC to set. Check for any improperly installed aftermarket accessories before continuing with this test.

1. Turn the ignition on for at least 60 seconds.
2. With a scan tool, read the active DTCs.

Is the DTC Active at this time?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test.

2. CHECK THE (F855) 5-VOLT SUPPLY CIRCUIT FOR A SHORT TO VOLTAGE
1. Turn the ignition off.
2. Disconnect all the Sensor harness connectors that share the (F855) 5-Volt Supply circuit.
3. Disconnect the APP Sensor harness connector.

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

4. Ignition on, engine not running.
5. Measure the voltage on the (F855) 5-Volt Supply circuit at the CKP Sensor harness connector.

Is the voltage reading above 5.2 volts?

Yes

- Repair the short to voltage in the (F855) 5-Volt Supply circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 3

3. (K852) 5-VOLT SUPPLY CIRCUIT SHORTED TO VOLTAGE
1. Measure the voltage at the (K852) 5-Volt Supply circuit at the APP Sensor harness connector.

Is the voltage reading above 5.2 volts?

Yes

- Repair the short to voltage in the (K852) 5-Volt Supply circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 4

4. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the related Sensors and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched, or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the related Sensor and Powertrain Control Module connectors.
4. Perform any Technical Service Bulletins that may apply.

Were there any problems found?

Yes

- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Replace and program the Powertrain Control Module (PCM). Powertrain Control Module - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.