Code Definition

P1891 — Transfer case contact plate ground return open

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Ford

About P1891

P1891 is a manufacturer-specific powertrain diagnostic trouble code recorded for Ford vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1891 is stored, the module has detected an open (broken or disconnected) electrical path in the monitored circuit.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1891 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The transfer case shift motor contact plate uses several signal channels, typically A through D, that all share a common ground return to complete their circuits back to the 4WD control module or PCM. The module reads the combination of these channels against the shared ground to determine transfer case position. DTC P1891 sets when the module detects an open in that ground return path, which removes the reference all the contact plate channels depend on and makes their signals unreadable or invalid. With this fault present the module cannot reliably confirm transfer case position, shifts may ...

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