P0642
P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW
For a complete wiring diagram, refer to the Wiring Information.
Theory of Operation
The primary 5-Volt Supply circuit supplies the Crankshaft Position Sensor (CKP), Oil Pressure Sensor (OPS), Throttle Body Assembly, A/C Pressure Transducer, and Accelerator Pedal Position (APP) Sensor 1. For self protection, if the 5-Volt Supply circuit is shorted to ground or if one of the sensors is internally shorted, the Powertrain Control Module (PCM) will turn off the 5-Volt Supply circuit until the next ignition cycle.
- When Monitored:
Ignition on.
- Set Condition:
When the Powertrain Control Module (PCM) recognizes the Primary 5-Volt Supply circuit voltage is too low. One Trip Fault. ETC light is flashing.
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.
1. ACTIVE DIAGNOSTIC TROUBLE CODE (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 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. (F855) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
1. Turn the ignition off.
2. Disconnect all of the sensor harness connectors that share the (F855) 5-Volt Supply circuit.
3. Disconnect the APP Sensor harness connector.
4. Disconnect the A/C Pressure Transducer harness connector.
5. Disconnect the PCM harness connectors.
6. Measure the resistance between ground and the (F855) 5-Volt Supply circuit at the Throttle Body Assembly harness connector.
Is the resistance above 1000 Ohms?
Yes
- Repair the short to ground 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 GROUND
1. Measure the resistance between ground and the (K852) 5-Volt Supply circuit at the APP Sensor harness connector.
Is the resistance above 1000 Ohms?
Yes
- Go To 4
No
- Repair the short to ground in the (K852) 5-Volt Supply circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
4. THROTTLE BODY ASSEMBLY
1. Reconnect all of the harness connectors except for the Throttle Body Assembly harness connector.
2. Turn the ignition on.
3. Measure the voltage at the (F855) 5-Volt Supply circuit in the Throttle Body Assembly harness connector.
Is the voltage below 4.75 Volts?
Yes
- Go To 5
No
- Verify that there is good pin to terminal contact in the Throttle Body Assembly and Powertrain Control Module connectors. If OK, replace the Throttle Body Assembly.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
5. CRANKSHAFT POSITION SENSOR
1. Turn the ignition off.
2. Disconnect the CKP Sensor harness connector.
3. Turn the ignition on.
4. Measure the voltage at the (F855) 5-Volt Supply circuit at the CKP Sensor harness connector.
Is the voltage below 4.75 Volts?
Yes
- Go To 6
No
- Verify that there is good pin to terminal contact in the CKP Sensor and Powertrain Control Module connectors. If OK, replace the Crankshaft Position Sensor.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
6. OIL PRESSURE SENSOR
1. Turn the ignition off.
2. Disconnect the Oil Pressure Sensor harness connector.
3. Turn the ignition on.
4. Measure the voltage at the (F855) 5-Volt Supply circuit at the Oil Pressure Sensor harness connector.
Is the voltage below 4.75 Volts?
Yes
- Go To 7
No
- Verify that there is good pin to terminal contact in the Oil Pressure Sensor and Powertrain Control Module connectors. If OK, replace the Oil Pressure Sensor.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
7. A/C PRESSURE TRANSDUCER
1. Turn the ignition off.
2. Disconnect the A/C Pressure Transducer harness connector.
3. Turn the ignition on.
4. Measure the voltage at the (F855) 5-Volt Supply circuit at the A/C Pressure Transducer harness connector.
Is the voltage below 4.75 Volts?
Yes
- Go To 8
No
- Verify that there is good pin to terminal contact in the A/C Pressure Transducer and Powertrain Control Module connectors. If OK, replace the A/C Pressure Transducer.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
8. ACCELERATOR PEDAL POSITION SENSOR
1. Turn the ignition off.
2. Disconnect the APP Sensor harness connector.
3. Turn the ignition on.
4. Measure the voltage at the (K852) 5-Volt Supply circuit at the APP Sensor harness connector.
Is the voltage below 4.75 Volts?
Yes
- Go To 9
No
- Verify that there is good pin to terminal contact in the Accelerator Pedal Position Sensor and Powertrain Control Module connectors. If OK, replace the Accelerator Pedal Position Sensor.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
9. 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.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.