B1390

Oil Temperature Sensor Circuit Short To Ground

Body Engine Cooling Oil Temperature Sensor 🟢 Low — Fix at next service ✅ Safe to Drive
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What This Actually Means

In plain language — no jargon

The oil temperature sensor is sending a signal that looks like it's shorted directly to ground, meaning the electrical connection is broken or faulty. It's like a water thermometer that's stuck giving a false "freezing" reading because the wire is damaged.

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Symptoms You May Notice

3 known symptoms for this code
Check Engine Light illuminated
Incorrect oil temperature display on dashboard
Engine may run rich or exhibit poor fuel economy
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECM monitors the oil temperature sensor's resistance and voltage signal. A short to ground causes the voltage to drop to 0V or near-zero, which the ECM interprets as an impossible sensor fault. The ECM expects a voltage range corresponding to valid oil temperatures between approximately -40°C and 150°C.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Sensor Voltage 0.5V to 4.5V (varies by temperature) 0V or below 0.2V (short to ground)
Oil Temperature Range -40°C to 150°C Reading below -40°C indicates short circuit
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Wiring harness connector
Inspect the oil temperature sensor connector for corrosion, moisture, or loose pins and clean or reseat as needed.
2
Sensor wiring
Check the wiring harness from the sensor to the ECM for cuts, abrasions, or bare wire touching ground and repair with electrical tape or replace the harness.
3
Oil temperature sensor
Replace the oil temperature sensor if wiring and connections are intact and the fault persists.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1390 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code B1390

What happens after you fix the fault

Once the fault is repaired, B1390 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.