B1387 — Oil Temperature Sensor Circuit Open

What is the most common cause of B1387?

The most common causes are: blown fuse or failed relay, damaged wiring in door jambs or wet areas, corroded or loose connectors.

Is it safe to drive with B1387?

Usually safe to drive — body codes rarely affect drivability. Exceptions: exterior lighting and wipers in bad weather, and central locking faults that can leave the car unsecured.

Will B1387 clear itself?

Sometimes B1387 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How do I diagnose B1387 myself?

Start with a scan: confirm B1387, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the oil temperature sensor, and verify the suspect component against live data before buying parts.

What does OBD2 code B1387 mean?

B1387 — Oil Temperature Sensor Circuit Open. A fault in the body electrical system. The car is usually drivable while you plan the repair. Typical causes: blown fuse or failed relay, damaged wiring in door jambs or wet areas, corroded or loose connectors.

The engine control module logs trouble code B1387 when it detects that the electrical pathway for the oil temperature sensor has been interrupted. Put another way, the circuit is open — meaning current cannot complete its loop back to the module. This is a body electrical fault, not an engine management one, even though the sensor itself monitors engine operating conditions.

When everything is working correctly, the oil temperature sensor sends a varying signal back to the module based on oil temperature. The module expects to see this signal within a certain range. If the circuit is broken, the module receives nothing — or an invalid reading — and after confirming the condition across multiple drive cycles, it sets B1387 and illuminates the check engine light. The freeze frame data stored alongside the code is particularly valuable here. It records engine load, RPM, coolant temperature, and vehicle speed at the exact moment the fault was detected, giving you precise conditions to replicate during diagnosis.

The underlying cause is almost always electrical: a cut or broken wire somewhere in the harness, a connector that has come unplugged or developed corrosion on its pins, a blown fuse feeding that particular circuit, or occasionally the sensor itself has failed internally. Physical damage from age, moisture intrusion, or movement at flex points like door hinges can all create an open circuit. The key point is that B1387 does not set from a single bad reading — the module needs to see the fault persist under specific operating conditions before it flags the problem.

Symptoms

• The check engine light or body system warning light turns on and stays on
• Engine performance remains unaffected in most vehicles — the car drives and runs normally
• One or more body electrical functions behave erratically or stop working entirely, depending on which circuit shares the affected wiring path (doors, windows, lighting, wipers)
• The fault may be intermittent, appearing only when the vehicle warms up or after hitting a bump that temporarily breaks a fragile connection
• In some cases, no obvious symptom exists beyond the illuminated warning light

Causes

• Blown fuse supplying the oil temperature sensor circuit or related body control circuits
• Broken or severed wire within the oil temperature sensor harness, often at pinch points or areas exposed to heat
• Connector that has backed out of its socket, has pins that are bent or pushed back, or has corrosion buildup preventing good electrical contact
• Oil temperature sensor itself has failed internally, creating an open circuit at the component
• Damaged wiring in door jambs, tailgate hinges, or other flex locations where wires bend repeatedly
• Loose, oxidized, or otherwise compromised connectors at the sensor or module side
• Faulty switch, actuator motor, or relay that shares the affected circuit
• Body control module has failed or is experiencing internal circuit issues

How to diagnose

1. Plug in an OBD2 scanner, retrieve B1387, and record the freeze frame data. These details show you the exact engine conditions — load, temperature, speed — present when the module first flagged the fault, and you will need to reproduce those conditions during your verification drive later.
2. Look for any additional stored codes. Related trouble codes often point toward the real culprit — a short or ground fault in a shared circuit, for example. Check manufacturer technical service bulletins for your specific make and model; some B-series codes have documented software corrections or known issues.
3. Perform a thorough visual inspection of the wiring and connectors associated with the oil temperature sensor and the body electrical system. Look for insulation cracks, wire strands visible through the jacket, greenish corrosion on pins, or any connector that appears loose.
4. With the harness disconnected at both ends, run a continuity test on the oil temperature sensor circuit from end to end. A reading other than near-zero ohms confirms an open somewhere in the path. While monitoring resistance, gently wiggle the harness — a fluctuating reading indicates an intermittent break.
5. Activate the affected function — locks, windows, wipers, whatever the associated system may be — and observe its switch and motor data in the scanner's live data stream. This tells you whether the problem is upstream in the control signal or downstream at the actuator.
6. Clear the code, then drive the vehicle under the exact conditions recorded in the freeze frame data. If B1387 returns, you have confirmed the fault is still present and the repair is not complete.

Repair options

Depending on what the diagnosis reveals, repair costs vary significantly:

• Wiring repair or connector replacement: $80–$250
• Switch or actuator replacement: $120–$450
• BCM repair or full replacement: $300–$900

How much does it cost to fix B1387?

Parts and labor at independent shop rates in the United States typically run between $80 and $900 depending on which component is at fault. The majority of cases involve wiring damage or a bad connector — both inexpensive to fix. BCM replacement is the most expensive scenario and should be your last resort after confirming no other cause exists. Spending time on a proper diagnosis before purchasing parts will almost always save you money, since the most costly fix is rarely the one hiding behind the code.

Can you drive with B1387?

Generally yes — B1387 is a body electrical fault and does not typically affect engine operation, transmission function, or safe handling. You can continue driving in most cases. That said, some scenarios warrant attention: if the fault involves exterior lighting, you lose visibility at night or in poor weather; if wipers are affected, your ability to see in rain or snow is compromised. A central locking malfunction could leave your vehicle unsecured or, in some cases, unable to be locked at all. Address these functions promptly even if the car otherwise drives normally.

Related OBD2 codes

• B1300: Power Door Lock Circuit Failure
• B1301: Power Door Lock Circuit Open
• B1302: Accessory Delay Relay Coil Circuit Failure
• B1303: Accessory Delay Relay Coil Circuit Open
• B1304: Accessory Delay Relay Coil Circuit Short To Battery
• B1305: Accessory Delay Relay Coil Circuit Short To Ground