Oil Temperature Sensor Circuit Open
The oil temperature sensor isn't sending a signal to the engine computer, like a broken thermometer that won't communicate its reading. The ECU can't monitor oil heat and may default to safe but inefficient engine operation.
The ECU monitors voltage from the oil temperature sensor to track engine oil heat and adjust cooling fan speed, transmission shift points, and fuel injection timing. An open circuit means zero or erratic voltage signal, triggering the fault code when the ECU detects a break in the sensor wiring or sensor failure.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Sensor Voltage | 0.5–4.5V (varies with temperature) | No signal or out-of-range voltage |
| Resistance | Decreases as temperature increases | Open circuit (infinite resistance) |
Code B1387 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.
Once the fault is repaired, B1387 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.