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DTC P0839: 4WD Mode Sensor High: Testing

  1. With the DRBIII®, record and erase DTCs. Start the engine and cycle the Transfer Case through all positions. With the DRBIII®, read DTCs. Does the DRBIII® display P0839-4WD MODE SENSOR HIGH? If yes, go to next step. If no, go to step  6.
  2. Turn the ignition off to the lock position. Disconnect the Powertrain Control Module harness connector. Disconnect the Transfer Case Position Sensor harness connector. Check connectors and clean/repair as necessary. Measure the resistance of the Transfer Case Position Sensor Input circuit from PCM harness connector to the Transfer Case Position Sensor harness connector. Is the resistance above 5.0 ohms? If yes, repair the Transfer Case Position Sensor input circuit for an open. If no, go to next step.
  3. Turn ignition on. Measure the voltage of the Transfer Case Position Sensor Input circuit at the Transfer Case Position Sensor harness connector. Is there any voltage present? If yes, repair the Transfer Case Position Sensor input circuit for a short to voltage. If no, go to next step.
  4. Turn the ignition off. Reconnect the Transfer Case Position Sensor connector. Measure the resistance between the Transfer Case Position Sensor Input circuit and the Sensor Return circuit at the PCM harness connector. Is the resistance between 55 ohms and 1.3 k/ohms? If yes, go to next step. If no, replace the Transfer Case Position Sensor.
  5. There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
  6. The conditions that set the DTC are not present at this time. Inspect the wiring and connectors specific to this circuit. Wiggle the wiring while checking for shorts and open circuits. Were any problems found? If yes, repair as necessary. If no, test is complete.
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