Oil Temp Sensor Circuit Malfunction
Diagnostic trouble code B1389 indicates that the powertrain control module (PCM) or body control module (BCM) has detected a fault in the oil temperature sensor (OTS) circuit. The sensor's voltage signal is outside the expected calibrated range, typically due to an open circuit, short to ground, or short to voltage. This prevents accurate calculation of oil viscosity and temperature, affecting engine control strategies or dashboard indications.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty oil temperature sensor (internal open or short)
- Signal circuit shorted to ground, voltage (B+), or open
- Damaged, corroded, loose, or pushed-back terminals in the sensor connector
- Internal PCM/BCM failure (rare)
3. Symptoms You Will Notice
- Check Engine Light or Service Engine Soon light illuminated
- Inaccurate oil temperature reading or no reading on the dashboard
4. Step-by-Step Diagnosis
Scan for additional codes and verify B1389 is present
Inspect the oil temperature sensor connector for damage, corrosion, or loose terminals
Check the sensor signal circuit for shorts to ground or voltage, and for open circuits using a multimeter
Test the oil temperature sensor resistance per manufacturer specifications
If all checks pass, suspect a PCM/BCM fault and perform further module diagnostics
5. Frequently Asked Questions
Is it safe to drive?▼
The vehicle may still be drivable, but inaccurate oil temperature readings can affect engine protection and performance. It is recommended to diagnose and repair the issue promptly to avoid potential engine damage.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on the cause. A sensor replacement is usually $50–$150 for the part plus labor, while wiring repairs may be $100–$200. PCM replacement, if needed, can exceed $500.