What causes fault code P0387?

• Most likely: Faulty Crankshaft Position Sensor (internal short) • Likely: Damaged wiring or corroded connectors (short to ground) • Possible: Damaged or dirty reluctor wheel (magnetic debris) • Rare: Faulty Engine Control Module (ECM)

How do you fix fault code P0387?

STEP 1: Inspect the connector for sensor B for corrosion or pushed-out pins. Clean as necessary. STEP 2: Measure circuit voltage. A Hall-effect sensor typically requires a 5V or 12V reference and a solid ground. Ensure the signal wire is not shorted to ground with the sensor disconnected. STEP 3: Use an oscilloscope to monitor the waveform (square wave) while cranking. The signal should be consistent without drops in amplitude. STEP 4: Inspect the reluctor wheel through the sensor port for broken teeth or metallic debris buildup. STEP 5: If wiring and mechanical components are verified, replace the Crankshaft Position Sensor.

Powertrain (Engine & Gearbox)Standard EOBD

P0387 - Crankshaft Position Sensor B Circuit Low

Q: What are the symptoms of fault code P0387?

• Check Engine Light (MIL) illumination • Engine hard to start or no-start condition • Engine stalling while driving • Rough idling and reduced engine power • Vehicle enters Limp-home mode

Last updated:1 February 2026

Related:Crankshaft Position Sensor (CKP), Wiring Harness, Reluctor wheel / Tandkrans, Engine Control Unit (ECU/ECM), Camshaft Position Sensor (CMP)

System

Powertrain (Engine & Gearbox)

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Cylinder 3 Misfire Detected

Technical Description

P0387 is set when the Engine Control Module (ECM) detects that the voltage signal from the Crankshaft Position (CKP) sensor 'B' is lower than the calibrated limit for a predetermined amount of time. The CKP sensor monitors engine RPM and crankshaft position by reading a reluctor wheel. This data is vital for ignition timing and fuel injection synchronization. A 'Low' circuit condition typically implies a short to ground, a loss of reference voltage, or a failing sensor internally. The ECM may use the Camshaft Position Sensor as a backup, but performance will be significantly degraded, often forcing 'Limp-home' mode.

Possible Causes

Faulty Crankshaft Position Sensor (internal short)

Damaged wiring or corroded connectors (short to ground)

Damaged or dirty reluctor wheel (magnetic debris)

Faulty Engine Control Module (ECM)

Symptoms

Check Engine Light (MIL) illumination

Engine hard to start or no-start condition

Engine stalling while driving

Rough idling and reduced engine power

Vehicle enters Limp-home mode

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P0387 - Crankshaft Position Sensor B Circuit Low

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P0387 - Crankshaft Position Sensor B Circuit Low

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