Crankshaft Position Sensor B Circuit Low Input
The P0387 code indicates that the Engine Control Module (ECM) has detected a low voltage signal from the crankshaft position sensor B circuit. This sensor monitors the rotational speed and position of the crankshaft, which is critical for engine timing and fuel injection. A low input means the voltage is below the expected range, often due to a faulty sensor, wiring issues, or a poor electrical connection. This can cause the engine to run poorly or not start.
01. Most Common Causes
- Faulty crankshaft position sensor B
- Damaged or corroded wiring/connectors in the sensor circuit
- Short to ground in the sensor signal circuit
- ECM internal fault (rare)
02. Symptoms You Will Notice
- Engine cranks but does not start
- Intermittent stalling or rough idle
- Check Engine Light illuminated
- Engine misfire or hesitation during acceleration
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for additional codes.
Step 2: Visually inspect the crankshaft position sensor B and its wiring for damage, corrosion, or loose connections.
Step 3: Measure the sensor's resistance and voltage output with a multimeter; compare to manufacturer specifications.
Step 4: Check for a short to ground in the signal circuit by disconnecting the sensor and testing continuity.
Step 5: If all else is fine, replace the crankshaft position sensor B and clear the code.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
No, it is not safe. The vehicle may stall unexpectedly or fail to start, leading to a potential accident or being stranded.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for a DIY sensor replacement, or $100 to $250 if professionally installed, including parts and labor.