P0387 high Severity

P0387: Crankshaft Position Sensor B Circuit Low Input

Engine may not start, rough idle, hesitation, loss of power

Overview

P0387 indicates low voltage input from the Crankshaft Position Sensor B circuit; common causes include sensor failure, wiring issues, or ECM faults

Common Symptoms

  • Check engine light illuminated
  • Engine may not start
  • Tachometer does not register RPM when cranking
  • Poor engine performance or hesitation
  • Reduced fuel economy

Most Common Causes

Faulty crankshaft position sensor B high

Sensor internal failure can result in insufficient signal voltage

Damaged wiring or poor connector connection high

Open circuits, shorts to ground, or corrosion drop voltage signal

ECM input circuit failure medium

Internal module driver faults or programming errors can mimic low signal

Reluctor wheel damage or interference low

Damaged reluctor wheel or metal debris may alter sensor waveform

Diagnostic Steps

  1. Scan vehicle with professional OBD-II scanner
    Expected: Retrieve P0387 and any related codes
    Interpretation: Confirms code and context for further diagnosis
  2. Visual inspection of sensor wiring and connectors
    Expected: No corrosion, broken wires, or loose pins
    Interpretation: Eliminate simple connection faults
  3. Measure voltage at CKP sensor B reference and ground
    Expected: Stable reference voltage (approx 5 V)
    Interpretation: Low voltage indicates wiring or sensor issue
  4. Test sensor output with multimeter/oscilloscope while cranking
    Expected: Consistent waveform and correct resistance per spec
    Interpretation: Weak or missing signal identifies sensor or circuit fault
  5. Check ECM input circuit if sensor and wiring pass tests
    Expected: Waveform at PCM matches sensor output
    Interpretation: Mismatch suggests wiring fault; identical failure points to ECM

Repair Solutions

Replace crankshaft position sensor B medium
Estimated Cost: $100 - $300

Most common fix if sensor fails resistance/waveform tests

Repair wiring harness and connectors medium
Estimated Cost: $50 - $200

Repair shorts, opens, and corrosion

ECM reprogramming or replacement hard
Estimated Cost: $300 - $1200

Consider only after eliminating sensor and wiring issues

Common Misdiagnoses

Avoid these common diagnostic mistakes:

  • Assuming sensor failure without checking wiring harness and connectors

Frequently Asked Questions

What does a P0387 diagnostic trouble code signify?

Crankshaft Position Sensor B Circuit Low Input is the standard definition for P0387. This diagnostic code is triggered when the ECU detects a problem in the Ignition.

Reflecting on severity: How bad is P0387?

This is a high priority issue. Engine may not start, rough idle, hesitation, loss of power

How do I know if I have code P0387?

Common symptoms include: Check engine light illuminated, Engine may not start, Tachometer does not register RPM when cranking. You might also notice the Check Engine Light is on.

Why is my car throwing a P0387 code?

Potential culprits include: Faulty crankshaft position sensor B, Damaged wiring or poor connector connection, ECM input circuit failure. A proper diagnosis is recommended.

Estimated repair costs for different causes of P0387

Repair costs depend on the specific failure. A simple Repair wiring harness and connectors replacement is relatively affordable ($50-$200), whereas a ECM reprogramming or replacement repair is more expensive, potentially reaching $1200.

Is P0387 a generic or manufacturer-specific code?

This is a universal code. You might see P0387 on Ford, Chevrolet, Toyota, Honda, Nissan, or any other OBD-II vehicle.

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