Tech Tip: Mercedes-Benz Low-Range Lamp Flashing/Code P1831 – UnderhoodService

Tech Tip: Mercedes-Benz Low-Range Lamp Flashing/Code P1831

If a customer with a 2004 ML 350 V6-3.7L reports that the low-range light flashes rapidly (18 times) after vehicle start with fault code P1831 (positioner motor, position sensor or power supply is faulty) in the transfer case ECU, do not replace the transfer case motor. This is caused by temporary loss of communication between transfer case control module and shift motor position sensor. To resolve the problem ....

If a customer with a 2004 ML 350 V6-3.7L reports that the low-range light flashes rapidly (18 times) after vehicle start with fault code P1831 (positioner motor, position sensor or power supply is faulty) in the transfer case ECU, do not replace the transfer case motor. This is caused by temporary loss of communication between transfer case control module and shift motor position sensor. To resolve the problem, read out the fault codes and cycle the transfer case shift motor by following the below procedure.

Service Procedure:
1. Read out and erase any fault codes.
2. If fault codes other than P1831 are present, diagnose and repair accordingly.
3. If fault code P1831 is present, start the vehicle.
4. Shift the transmission into neutral (N).
5. Push the low-range switch. Depress the brake pedal.
6. After the shift motor has cycled, push the low range switch again. The low-range light should go out at this time.
7. Confirm the proper transfer case shift function: Cycle the ignition and repeat steps 2-5.

Warning: While performing the transfer case shift adaptation described above, take all necessary safety measures, such as applying the parking brake and holding the service brake firmly. (Failure to do so can result in unintended vehicle movement.)

Technical service bulletin courtesy of ALLDATA.

For additional information, visit www.alldata.com.

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