Damaged, chafed or corroded wiring to the crankshaft sensor B, including intermittent open or short circuits; Loose, corroded or contaminated sensor connector pins; Failing crankshaft position sensor B that drops out when hot or vibrating; Damaged or dirty reluctor wheel or trigger ring, or excess sensor air gap from a loose mounting; Oil or metallic debris on the sensor tip affecting the signal; Low or unstable supply voltage or poor earth affecting the sensor signal; Fault within the engine control unit.

P0389

Crankshaft Position Sensor B Circuit Intermittent.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
3: AreaIgnition system or misfire
89: FaultThe specific fault in that area

What it means

P0389 means the engine control unit has detected an intermittent fault in the crankshaft position sensor 'B' circuit. The signal from this second crankshaft sensor has dropped out, become erratic or gone missing briefly while the engine was running or cranking. The definition is generic, so which sensor counts as 'B' and where it sits depends on the model and engine.

Symptoms

Intermittent engine misfire or stumbling
Engine cuts out suddenly then restarts
Long cranking or intermittent no-start
Rev counter flickering or dropping to zero
Hesitation or loss of power
Engine warning light on

Possible causes

Damaged, chafed or corroded wiring to the crankshaft sensor B, including intermittent open or short circuitslikely
Loose, corroded or contaminated sensor connector pinslikely
Failing crankshaft position sensor B that drops out when hot or vibratinglikely
Damaged or dirty reluctor wheel or trigger ring, or excess sensor air gap from a loose mountingpossible
Oil or metallic debris on the sensor tip affecting the signalpossible
Low or unstable supply voltage or poor earth affecting the sensor signalpossible
Fault within the engine control unitrare

How to diagnose

Read all stored and pending codes and check the freeze frame data for engine speed, load and temperature when the fault set
Check for related codes such as other crankshaft or camshaft sensor faults, misfire codes or low voltage codes
Inspect the sensor, its wiring and connector for chafing, heat damage, oil contamination, bent pins and corrosion
With the engine running, wiggle the harness and connector while watching live engine speed data for dropouts
Check the sensor is secure and its mounting and air gap are correct for that engine
Inspect the sensor tip for debris and the reluctor wheel for damage, missing teeth or runout, as access allows
Test the sensor supply, earth and signal wiring against the manufacturer's wiring diagram and specification
Check battery condition and charging voltage, and compare crankshaft and camshaft signals on a scope if the fault persists

How to fix

Repair or replace damaged wiring, and clean and secure the connector, replacing terminals where corroded
Replace the crankshaft position sensor B if it fails testing or drops out
Clean oil or debris from the sensor area and fix any leak that is contaminating it
Correct the sensor mounting or replace a damaged reluctor wheel or trigger ring
Repair battery, charging or earth faults that cause unstable voltage

Can I keep driving?

High severity

Avoid driving until it is diagnosed, as the engine may cut out without warning, which is unsafe in traffic and can leave you stranded. If it must be moved, keep it to a short, careful trip.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.