Engine

P0389 — Crankshaft Position Sensor B Circuit Intermittent

Severity: high Drive with care, to a shop

What P0389 means

The engine control unit detected a signal from crankshaft position sensor B that drops out or is erratic. This sensor tells the ECM how fast the crankshaft turns and where it is in its rotation, which is used to time ignition and fuel injection. When the signal is unreliable, the ECM can lose synchronization and the engine may run poorly or stall.

Symptoms

  • Check Engine light on, either steady or intermittent
  • Hard starting or no start
  • Intermittent stalling or rough idle
  • Hesitation or loss of power when accelerating
  • Tachometer does not move while cranking

Possible causes

  1. Failed crankshaft position sensor B
  2. Damaged or corroded wiring or connector at the sensor
  3. Loose or poor connections in the connector or harness
  4. Open, shorted or chafed signal wire
  5. Rarely, an internal ECM fault or software problem

How to diagnose

  1. Read codes and freeze frame data to see when the fault set
  2. Inspect the sensor, connector and harness for oil, chafing, corrosion and broken locking tabs
  3. Wiggle the harness and connector with the engine running while watching RPM on a scan tool
  4. Test power, ground and signal wires with a multimeter using the factory wiring diagram
  5. Scope the sensor signal during cranking and while running
  6. Check sensor mounting, air gap and the condition of the reluctor wheel
  7. Compare the signal against the camshaft sensor for correct sync
  8. Consider the ECM only after the sensor and wiring are cleared

Common fixes

  • Clean and secure the sensor connector
  • Repair or replace damaged wiring and connector terminals
  • Replace crankshaft position sensor B
  • Reprogram or replace the ECM if confirmed faulty

Questions and answers

What does code P0389 mean?

It means the signal from crankshaft position sensor B is dropping out or unstable. The ECM then has trouble tracking crankshaft position, which can upset ignition timing and fuel delivery.

Can I drive with P0389?

Only a short distance to a repair shop, and with caution. The engine can stall at any time and may not restart, which is dangerous in traffic.

What most often causes P0389?

Usually the sensor itself or a poor connection in its wiring or connector. Start with a careful inspection of the harness and plug, then test the sensor.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.