P0389: Crankshaft Position Sensor "B" Circuit Intermittent
The crankshaft position sensor B signal drops out for short moments.
High risk
The engine may stall or start hard. Have it checked before longer trips.
Short answer · Can I keep driving with P0389?
With care. Engines with a second crankshaft sensor can usually run on the first one, but starting and running may suffer. Have it checked soon.
What does P0389 mean?
Code P0389 means pulses from crankshaft sensor B are sometimes missing. A loose connector, a chafed wire or a sensor that fails when hot are typical causes. Only some engines have a second crankshaft sensor.
What the car does when the code is set
The check engine light may come on. The engine may stall, stutter or not start at all. Because the rev counter often uses this signal, it may drop to zero just before the engine stops.
How the system works
The crankshaft position sensor reads a toothed wheel on the crankshaft or flywheel. A gap of one or two missing teeth marks a reference position. From these pulses, the engine control unit calculates the engine speed and the exact position of the pistons, which it needs to fire the injectors and spark plugs at the right moment. It is also used for misfire detection. If the signal disappears, most engines cannot run, so a fault in this circuit can stop the engine without warning.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Faulty crankshaft position sensorHeat cycles often make these sensors fail, sometimes only when hot.
- Wiring or connector faultChafed or oil-soaked wiring near the sensor.
- Damaged reluctor (trigger) wheelMissing or bent teeth give an irregular signal.
- Metal debris on the sensorMagnetic sensors pick up metal particles.
How it is diagnosed
- Check the connector and wiringLook for oil, corrosion and damaged insulation.
- Check the rpm signal while crankingIf the scan tool shows no engine speed while cranking, the control unit is not receiving the signal.
- Measure the sensorCheck resistance or the signal with an oscilloscope, as described in the service data.
- Inspect the sensor tip and trigger wheelRemove the sensor and check it for debris and damage.
Questions about P0389
Does every engine have crankshaft sensor B?
No. Most engines have only one crankshaft sensor. The service data shows whether sensor B exists and where it is fitted.
Why does the engine stall only when hot?
Crankshaft sensors often fail when hot and work again after cooling down. That pattern is a typical sign of this code.
Will a new sensor fix a no-start?
Only if the sensor is the cause. Check the rpm reading while cranking: if it stays at zero, the signal is missing.