P0385 sets when the powertrain control module (PCM) detects an abnormal voltage or frequency signal from the crankshaft‑position sensor B circuit. The fault can stem from the sensor itself, its wiring/connector, the reluctor wheel, or (very rarely) an internal PCM issue. When this code is active the engine may run poorly, stall, or fail to start because the PCM can no longer reliably determine crankshaft position.
Internal winding failure, contamination, or mechanical wear can cause the sensor to produce an out‑of‑range signal.
Open circuits, shorts to ground or voltage, broken wires, corroded pins, or poor terminal contact can disrupt the sensor’s signal.
Improper air gap or loose mounting can reduce magnetic coupling, producing weak or intermittent signals.
Missing, bent, or debris‑covered teeth on the crankshaft‑mounted reluctor can cause irregular waveform generation.
A weak or fluctuating 5 V reference voltage or poor ground return can make the sensor output erratic.
The PCM may fail to process the sensor signal correctly, but this is the least common cause and should be ruled out only after all other components are verified.
No. The crankshaft position sensor B and its wiring are far more likely culprits. The PCM should only be considered after the sensor, connectors, and circuit have been verified as good.
Yes. Metal debris, oil, or rust on the tone wheel can distort the magnetic field and produce an erratic signal, setting the code.
Often the engine will run in a limited ‘limp’ mode or may stall completely, depending on whether the PCM can still calculate crank position from the other sensor (if equipped).
Many modern engines use two sensors (A and B) for redundancy and to differentiate position; some older designs use only one. The presence of a ‘B’ sensor depends on the specific engine architecture.