DTC codes / P08xx · Transmission / P0838
P0838 indicates that the powertrain control module (PCM) has detected a low-voltage condition on the four-wheel-drive (4WD) switch circuit, meaning the signal wire is shorted to ground or the switch is stuck in a closed state. The PCM expects to see a voltage that toggles between high and low as the 4WD switch changes position, but it is continuously seeing a low voltage when it should be high.
Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.
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