Code
B1389
Other
B — Body
Oil Temperature Sensor Circuit Failure
AI status
Completed
Completed
100%
Causes
- Open circuit in sensor wiring
- Short to ground or short to battery in sensor circuit
- Corroded or loose sensor connector
- Failed oil temperature sensor (thermistor or sender)
- Oil contamination or internal sensor damage
- Poor ground or reference voltage supply
Symptoms
- Malfunction indicator lamp (MIL) or service light illuminated
- Incorrect or missing oil temperature reading on dash
- Engine management may adjust fuel/shift strategy incorrectly
- Cold/hot start drivability changes or prolonged warm-up
- Possible stored or pending drivability-related trouble codes
What to check
- Read stored/active codes and freeze frame with a scan tool
- Inspect sensor connector and wiring for oil ingress, corrosion, damage
- Back-probe sensor connector to observe live voltage or resistance values
- Compare live oil temp reading to ambient/engine temperature and known behavior
- Wiggle harness while monitoring live data to detect intermittent faults
- Check continuity and resistance from sensor to ECU connector
Signal parameters
- Sensor type: typically a thermistor (NTC) or resistive sender; output varies with temperature
- Voltage-style sensors: output typically in the 0–5 V range (vehicle-specific)
- Thermistor behavior: higher resistance at cold, lower resistance at hot (values vary by sensor)
- Response should change smoothly as oil temperature rises; spikes or fixed values indicate fault
- Exact resistance/voltage specifications are vehicle-specific — consult OEM data
Diagnostic algorithm
- Retrieve B1389 and any related codes with a scan tool; record freeze frame and live oil temperature reading.
- Visually inspect the oil temperature sensor, connector, and wiring for oil contamination, corrosion, loose terminals or physical damage.
- With ignition ON (engine off), back-probe connector and verify reference voltage/pull-up and ground presence per vehicle service info. If passive, measure resistance across sensor terminals.
- Measure sensor resistance at ambient temperature and compare to OEM specification (or monitor voltage and compare to expected behavior).
- Warm the engine slightly and monitor the sensor response; resistance/voltage should change smoothly with temperature.
- Perform a wiggle test of the harness while monitoring live data to find intermittent opens/shorts.
- Check continuity from the sensor connector to the ECU connector; inspect for short to ground or battery on the circuit.
- Repair any damaged wiring, terminals, or grounds. Clean or replace corroded connectors and ensure proper sealing against oil.
- If wiring and connectors are good but readings remain out of specification, replace the oil temperature sensor.
- After repairs, clear codes, perform a road/drive cycle or warm-up test and re-scan to confirm the fault does not return.
Likely causes
- Damaged or disconnected sensor connector
- Broken or chafed wiring between sensor and ECU
- Failed oil temperature sensor
- Corrosion or oil intrusion at connector causing high resistance/intermittent
- Poor ground or blown fuse affecting sensor reference/power
Fault status
Status
Oil Temperature Sensor Circuit Failure — open, short, intermittent, or out-of-range signal from oil temperature sender or its wiring/connector.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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