What it means
The ECU detects intermittent dropouts on the fuel temperature sensor B circuit. Loose connector, chafed wiring or sensor failing under thermal load.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Fuel temperature sensor B sends a temperature signal from its monitored fuel location to the engine control module. P0189 sets when that signal becomes erratic or drops out intermittently, often as a loose or damaged connection reacts to heat or vibration.
Common causes
Most likely first.
- Connector loose or corroded
- Wiring chafed
- Connector with intermittent contact under vibration
Symptoms
- Check engine light on
- Intermittent hard starting or rough running
- Intermittent loss of power
How to diagnose it
- Review freeze-frame data and live fuel temperature B readings for sudden dropouts or implausible jumps, noting engine temperature and operating conditions when they occur.
- Inspect sensor B's connector for looseness, corrosion, moisture, and pins that are bent or pushed back.
- While watching the live reading, gently move the harness and connector around sensor B to see whether vibration or movement reproduces the dropout.
- Check the sensor B wiring for chafing and test continuity and connection quality while flexing suspect sections.
- If the circuit remains sound, test fuel temperature sensor B under the conditions that trigger the fault and replace it if its signal becomes intermittent.
Common fixes
- Secure a loose sensor B connector and repair worn harness supports.
- Clean corroded contacts or replace damaged connector terminals.
- Repair chafed wiring in the fuel temperature sensor B circuit.
- Replace sensor B if it drops out when hot or vibrating despite sound wiring.
Can I keep driving?
If the engine is running smoothly, drive only as needed and avoid heavy loads until the intermittent fault is found. Because power loss or rough running can recur unexpectedly, stop if the engine begins to stall or lose power.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.