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 is critical for engine timing and fuel injection synchronization. A low input can result from a faulty sensor, damaged wiring, poor electrical connections, or issues with the sensor's reference voltage or ground circuit. This condition may cause the engine to run poorly or not start at all.
1. Most Common Causes
- Faulty or internally worn crankshaft position sensor B (CKP B)
- CKP B circuit wiring shorted to ground
- CKP B circuit wiring shorted to another low-voltage circuit
- Excessive resistance in the sensor circuit due to corroded connectors or poor splices
- Damaged, misaligned, or contaminated reluctor ring or tone wheel
- Internal ECM/PCM failure (less common)
2. Symptoms You Will Notice
- Engine cranks but does not start
- Engine misfires or runs rough
- Check Engine Light illuminated
- Reduced fuel economy and performance
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Visually inspect the crankshaft position sensor B wiring and connector for damage, corrosion, or loose connections.
Step 3: Test the sensor's resistance and voltage output using a multimeter; compare with manufacturer specifications.
Step 4: Check the sensor's reference voltage (typically 5V) and ground circuit at the connector.
Step 5: If all tests pass, suspect an intermittent issue or ECM fault; perform a wiggle test while monitoring the signal.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
No, it is not safe. The engine may stall or fail to start, leading to a breakdown or unsafe driving conditions.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on the vehicle and shop rates.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.