P0642 Sensor Reference Voltage 1 Circuit Low

P0642 Code - The primary 5-volt supply circuit supplies the Crankshaff Position Sensor (CKP). Oil Pressure Sensor (OPS), and Throttle Body Assembly.

P0642


For self protection, if the 5-volt supply circuit is shorted to ground or if one the sensors is internally shorted, the Powertrain Control Module (PCM) will turn off the 5-volt supply until the next ignition cycle. When the Powertrain Control Module (PCM) recognizes the 5-volt supply circuit voltage is too low. One trip fault. ETC light flashing.


Possible causes P0642 Code

  • 5-volt supply shorted to ground
  • Crankshaft position sensor
  • Oil Pressure Sensor
  • A/C pressure transducer
  • Throttle Body Assembly
  • APP sensor
  • Powertrain Control Module (PCM)


Diagnose P0642 Code


Step 1. Active DTC
Improperly installed aftermarket accessories can cause this DTC to set. Check for any improperly installed aftermarket accessories before continuing with this test.
Turn the ignition on for 60 seconds, with the scan tool read the active DTCs.

Is the DTC active at this time?

Yes, go to step 2.
No, perform the PCM intermittent condition.

Step 2. Check the 5-volt supply circuit and the 5-volt supply circuit for a short to ground
Turn the ignition off, disconnect the PCM harness connector. Disconnect all the sensors that share the 5-volt supply circuit, disconnect the APP sensor harness connectors. Measure the resistance between ground and the 5-volt supply circuit in the Throttle Body harness connector. Measure the resistance between ground and the 5-volt supply circuit in the APP harness connector.

Is the resistance above 10k Ohms in both circuits?

Yes, go to step 3.
No, repair the 5-volt supply circuit or the 5-volt supply circuit for a short to ground.

Step 3. Crankshaft Position Sensor
Reconnect the PCM harness connectors, reconnect all the previously disconnected sensors except for the CKP sensor harness connector. Ignition on, engine not running, measure the voltage on the 5-volt supply circuit in the CKP sensor harness connector.

Is the voltage below 4.5 volts?

Yes, go to step 4.
No, verify that there is good pin to terminal contact in the CKP sensor and Powertrain Control Module (PCM) harness connectors. If OK, replace the Crankshaft Position Sensor.

Step 4. Sensor shorted to ground
Measure the voltage on the 5-volt supply circuit at the CKP sensor harness connector. 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 5-volt supply circuit, one at a time including the APP sensor harness connector.

Does the voltage increase above 4.5 volts when disconnecting any of the sensor harness connectors?

Yes, verify that there is good pin to terminal contact in the related sensor and Powertrain Control Module connectors. If OK, replace the sensor that causes the 5-volt supply circuit voltage to increase when disconnected.

No, go to step 5.

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