P0189 - Fuel Temperature Sensor B Circuit Intermittent
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0189 is stored when the Engine Control Module (ECM) detects an intermittent or erratic voltage signal from the Fuel Temperature Sensor 'B'. The sensor is a Negative Temperature Coefficient (NTC) thermistor that provides a signal used by the ECM to calculate fuel density and adjust fuel delivery. Intermittent circuit faults are typically caused by poor electrical connections, chafed wiring, or internal sensor failure where the circuit breaks momentarily due to vibration or thermal expansion.
Possible Causes
Poor electrical connection or oxidation in sensor B connector
Damaged wiring harness (chafed or broken) near engine vibration points
Defective fuel temperature sensor (internal intermittent break)
Faulty Engine Control Module (ECM) input circuit
Symptoms
Recommended Solution
- Visual inspection: Check sensor B connector for corrosion or bent pins. Clean with contact cleaner. Inspect wiring harness for chafing.
- Measurement: Verify 5V reference voltage from ECM with ignition ON. Measure sensor resistance; typically 2000-3000 Ohms at 20°C (68°F) - check manufacturer specs.
- Advanced diagnosis: Use an oscilloscope or scan tool 'Live Data' to observe temperature graph spikes while wiggling the harness to isolate the intermittent break.
- Component replacement: Replace sensor B if it fails resistance tests or exhibits internal drops in signal during vibration testing.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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