P0387
UniversalCrankshaft Position Sensor B Circuit Low Input
High SeverityThe P0387 code indicates that the Powertrain Control Module (PCM) has detected a low voltage signal from the Crankshaft Position Sensor B circuit. This fault can lead to significant engine performance issues, including no-start conditions or stalling while driving.
⚠️ Before You Begin (Safety First)
Always ensure the engine is cool before working on any engine components to avoid burns. Disconnect the battery's negative terminal before performing any electrical work to prevent accidental short circuits or electrical shock. Use appropriate jack stands if lifting the vehicle.
Common Symptoms
- Check Engine Light illuminated
- Engine cranks but won't start
- Engine stalls unexpectedly
- Rough idle
- Poor acceleration
- Engine misfires
- Reduced fuel economy
Common Causes
- Faulty Crankshaft Position Sensor B
- Damaged, corroded, or shorted wiring or connectors in the sensor circuit
- Poor electrical connection at the sensor or PCM
- Faulty Powertrain Control Module (PCM) (rare)
- Excessive metallic debris on the sensor tip (less common)
Frequently reported on: General/Universal
Diagnostic Steps
- Inspect the Crankshaft Position Sensor B and its wiring for any visible damage, frayed wires, corrosion, or loose connections.
- Check the sensor connector for bent pins or contamination.
- Clear the code using an OBD-II scanner and test drive the vehicle to see if the code returns.
- If no visible issues are found and the code returns, consider replacing the Crankshaft Position Sensor B.
- After replacement, clear the code again and test drive the vehicle.
- If the code persists, further electrical diagnostics may be required to test the circuit's continuity and resistance, and potentially the PCM inputs.
- Verify proper crankshaft sensor alignment if applicable to your vehicle model.
👨🔧 When to Call a Professional
If the P0387 code persists after checking the wiring and replacing the Crankshaft Position Sensor, or if you suspect more complex electrical issues beyond a simple sensor replacement, it's best to consult a professional mechanic or automotive electrician. They have specialized diagnostic tools to pinpoint intermittent electrical faults or PCM problems.
Commonly Asked Questions
What is a Crankshaft Position Sensor B and why is it important?
The Crankshaft Position Sensor B monitors the rotational speed and position of the crankshaft, sending this data to the PCM. This information is critical for the PCM to accurately control engine timing, fuel injection, and ignition, ensuring the engine runs smoothly and efficiently.
Can I drive my car with a P0387 code?
It is not recommended to drive with a P0387 code. A faulty crankshaft position sensor can cause severe drivability issues like engine stalling, no-start conditions, or unpredictable engine behavior, which can be dangerous.
How can I confirm the Crankshaft Position Sensor B is faulty?
After visually inspecting the wiring for damage, you can test the sensor's resistance or signal output using a multimeter or oscilloscope according to your vehicle's service manual specifications. A P0387 specifically points to a low input, often indicating an internal sensor fault or a wiring issue causing a voltage drop.
Is replacing the Crankshaft Position Sensor B a difficult DIY repair?
The difficulty varies greatly by vehicle make and model. In some cars, the sensor is easily accessible; in others, it may require removing other components like the starter or intake manifold, making it a moderately challenging repair for a DIY mechanic.
What are common mistakes to avoid when addressing P0387?
A common mistake is not thoroughly checking the wiring and connectors before replacing the sensor. Always ensure the new sensor is properly seated and the electrical connection is secure. Also, make sure to clear the codes after the repair to allow the PCM to relearn.