Code Definition

P0387 — Crankshaft Position Sensor B Circuit Low Input

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0387

P0387 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0387 is stored, the module has detected a signal or supply voltage lower than the expected operating range; and a sensor-related fault — the reported value from the named sensor is out of spec.

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.

Because P0387 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The powertrain control module (PCM) sets this code when it detects an abnormally low voltage signal from Crankshaft Position Sensor (CKP) 'B'. This typically indicates a short to ground, a weak sensor signal, or an issue with the wiring. Since the CKP sensor is critical for ignition timing and fuel injection synchronisation, a failure can lead to engine stalling, no-start conditions, or poor performance.

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