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Do you own or have access to a NGS (New Generation Star) or equivalent scan tool?
No I do not
In order to properly diagnose the problem the scan tool is required
Check the status of the contact plate switches in the data functions of the generic electronic module through the scan tool. In the normal 2WD position of the shift motor, contact plates A, B, and D should all indicate the same value and contact plate C should read the opposite (open or closed) value. If the contact plate values all indicate the same value as suggested by code P1891, disconnect the shift motor 8-pin connector and recheck the readings to determine if they are all still indicating the same status. Check the Yellow/White (YE/WH) wire to verify it is a good ground to the shift motor connection. This circuit is supplied a ground from the generic electronic module. If it is a questionable ground, check the circuit for an issue between the connector and the generic electronic module and service it as necessary. If the YE/WH wire is a good ground, install a jumper wire between the YE/WH wire and the OG/WH wire. This should result in a change of the status of contact plate D. Jumpering the Brown/White (BR/WH) wire to the YE/WH wire should result in a change of the status of contact plate C. Jumpering the White (WH) wire to the YE/WH wire should result in a change of the status of contact plate B. Jumpering the Violet/Yellow (VT/YE) wire to the YE/WH wire should result in a change of the status of contact plate A. If the contact plate status values of all switches change when the jumper is installed between said circuits, it indicates a failure of the 4WD shift motor due to the contact plate switches. If there is no change in one or more of the contact plate switch status values after the installation of the jumper wire, check the circuits for a problem between the shift motor and generic electronic module and service them as necessary before condemning the generic electronic module.
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can you tell me where the module is located? Is it located behind the radio?
Yes that is correct.
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