What Does B1390 Mean?
This code indicates that the Body Control Module (BCM) or related control module has detected an abnormally low voltage in the oil temperature sensor circuit, indicating a short circuit to ground. The sensor or its wiring is providing a reading below the acceptable voltage threshold, suggesting that current is finding an unintended path to chassis ground. This prevents accurate monitoring of engine or transmission oil temperature.
Common Causes
40%
Damaged or chafed wiring harness causing the signal wire to contact ground
30%
Failed oil temperature sensor with internal short to ground
20%
Corroded or moisture-damaged sensor connector causing ground path
10%
Control module internal fault or damaged control module connector
Diagnostic Steps
1
Step 1: Perform visual inspection of the oil temperature sensor connector and wiring harness from sensor to control module, looking for damaged insulation, pinched wires, corrosion, oil contamination, or signs of wires contacting metal components
2
Step 2: Disconnect the oil temperature sensor connector and measure resistance between the sensor signal terminal and vehicle ground using a digital multimeter; reading should be infinite (open circuit) - any continuity indicates a short to ground in the sensor itself
3
Step 3: With sensor still disconnected, measure resistance between the signal wire terminal at the harness connector and vehicle ground; infinite resistance indicates wiring is intact, while any continuity confirms wiring harness has a short to ground
4
Step 4: If wiring harness shows short to ground, trace and inspect the entire harness routing, paying special attention to areas where harness passes near sharp edges, heat sources, or moving components; repair or replace damaged section
5
Step 5: If sensor shows internal short, replace the oil temperature sensor and verify proper connector seal to prevent moisture ingress
6
Step 6: Clear codes and perform a test drive, monitoring live data for oil temperature readings within normal range (typically 180-250°F depending on vehicle) to confirm repair
Estimated Repair Cost
$75 - $350
Parts + labor, varies by vehicle and location
This code indicates that the Body Control Module (BCM) or related control module has detected an abnormally low voltage in the oil temperature sensor circuit, indicating a short circuit to ground. The sensor or its wiring is providing a reading below the acceptable voltage threshold, suggesting that...
The most common cause of B1390 (Oil Temperature Sensor Circuit Short To Ground) is: Damaged or chafed wiring harness causing the signal wire to contact ground
Typical repair costs for B1390 range from $75 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is generally safe to drive short distances, but the control module cannot accurately monitor oil temperature which may affect transmission shift patterns, engine performance strategies, or fail to warn of overheating conditions. Avoid extended highway driving or heavy loads until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1390 to identify the root cause.
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Quick Info
Category
Body
System
Engine Oil Temperature Monitoring System / Transmission Oil Temperature Monitoring
Difficulty
Type
Manufacturer
Recommended Tools
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