Code
B1389
ALFA ROMEO
B — Body
Oil temperature sensor
Views:
UK: 7
EN: 9
RU: 8
AI status
Completed
Completed
100%
Causes
- Damaged or failed oil temperature sensor
- Wiring open, short to ground or short to voltage in sensor circuit
- Corroded, loose or contaminated connector
- Poor ground or supply voltage to the sensor
- Incorrect sensor installed or out-of-spec replacement
- Intermittent fault caused by chafing or vibration
Symptoms
- Check Engine light or instrument cluster warning active
- Incorrect oil temperature reading on dash or no reading
- Cold-start enrichment or fuel trim issues (if ECU uses oil temp)
- Poor idle, rough running or unexpected engine behavior when oil temperature is used by control strategies
- Intermittent faults or hard-to-reproduce warnings
What to check
- Scan for stored freeze frame data and live oil temperature sensor readings with a diagnostic scan tool
- Visually inspect sensor, connector and harness for damage, corrosion, oil contamination and secure fit
- Back-probe sensor connector and check supply voltage and ground
- Measure sensor resistance (with engine cold) and compare to expected resistance vs temperature curve
- Wiggle harness and connector while monitoring live data to reproduce fault
- Check for related codes (power/ground or communication faults)
Signal parameters
- Typical oil temperature sensor type: NTC thermistor (resistance decreases as temperature increases)
- Nominal resistance examples (typical ranges, manufacturer-specific values vary): ~20–40 kΩ at -40°C, ~8–12 kΩ at 25°C, ~1–3 kΩ at 100°C
- Typical sensor signal voltage to ECU: approx. 0.2–4.8 V depending on temperature and circuit (varies by vehicle)
- Supply/reference voltage to sensor circuit: commonly 5 V reference from ECU (verify with wiring diagram)
Diagnostic algorithm
- Retrieve and record freeze frame and live data for oil temperature. Note sensor behavior at ambient temperature and during warm-up.
- Visually inspect sensor, connector and harness for oil contamination, bent pins, corrosion, broken wires, chafing or heat damage.
- With ignition ON (engine off), check reference voltage at the sensor connector; verify proper ground. Record values.
- Measure sensor resistance at ambient temperature and compare to manufacturer specification or a typical NTC curve. If resistance is out of expected range, replace sensor.
- If resistance is correct, back-probe sensor signal while warming engine and observe voltage/resistance change. If signal does not change smoothly with temperature, suspect wiring, connector or ECU input.
- Perform continuity and insulation tests on harness between sensor and ECU. Repair any opens or shorts; repair corroded connectors or pins.
- After repairs or sensor replacement, clear codes and perform a road or warm-up test while monitoring live oil temperature to confirm correct operation and that code does not return.
- If wiring and sensor check good but fault persists, consult wiring diagrams and consider ECU input circuit testing or replacement by qualified technician.
Likely causes
- Failed oil temperature sensor (NTC/thermistor)
- Broken or shorted harness between sensor and ECU
- Corroded connector pins at sensor or ECU
- Oil contamination or physical damage to sensor
- Aftermarket sensor with different resistance curve
Fault status
Status
Control unit detected an implausible or out-of-range oil temperature sensor signal (open, short, or incorrect resistance/voltage).
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email