Code Definition

P1812 — 4WD Mode Select Switch circuit open

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

About P1812

P1812 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 P1812 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.

P1812 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

This DTC is triggered when the 4WD control module or powertrain control module (PCM) detects an open circuit in the 4WD mode select switch input. The module monitors the resistance or voltage from the mode select switch to determine the driver request for 2WD, 4WD High, or 4WD Low. If the circuit reads open, the module cannot determine the switch position and sets the fault. The driver may find that 4WD mode changes are ignored, the system defaults to a single mode, and a warning indicator illuminates.

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