B1387 — Oil Temperature Sensor Circuit Open

The diagnostic trouble code B1387 indicates an issue with the oil temperature sensor circuit. This sensor measures the temperature of the engine oil, which is crucial for engine management and protection. When the circuit is open or malfunctioning, it sends incorrect or no data to the vehicle’s Engine Control Unit (ECU). Note that labels for this code may vary between manufacturers, and different OEMs might assign different codes or descriptions for similar issues.

Manufacturer variations for trouble code B1387

The code B1387 may be labelled differently depending on the vehicle manufacturer. Some OEMs may assign alternative codes or descriptions for similar circuit open issues related to the oil temperature sensor. It’s important to reference the vehicle-specific diagnostic manual, but common variations include:

• Toyota: C1400 or similar codes linked to oil temperature sensor circuit
• Ford: P2380 (though this is typically for turbocharger boost control, some Ford models may use alternative codes)
• Volkswagen / Audi: Codes starting with « B » related to sensor circuit open or short to ground
• Honda: Sensing codes like B1387 linked to oil temperature sensor circuit issues

Always verify the specific manufacturer diagnostic manual or OE documentation to confirm the exact code and description, as it can vary between makes and models.

What does trouble code B1387 mean?

The ECU (Engine Control Unit), which is the vehicle’s central computer, constantly monitors various sensors to ensure proper engine operation. The oil temperature sensor provides data about the oil’s temperature, helping to manage engine lubrication, cooling, and efficiency. When the circuit that connects this sensor to the ECU detects an open or malfunction, it triggers the B1387 code.

This malfunction could be caused by a broken wire, damaged connector, or a faulty sensor. The code is typically triggered when the ECU detects no voltage or an inconsistent voltage signal from the circuit over time. The problem sometimes appears suddenly during driving, or after work has been done on the sensor or wiring harness.

Severity and risks of trouble code B1387

The risks associated with this code depend on how long the issue persists and the vehicle’s design. An open circuit on the oil temperature sensor can cause the ECU to receive no data or false readings, which might lead to inappropriate engine management decisions. In some cases, the vehicle may default to a safe mode to protect the engine, limiting performance.

In the worst-case scenario, if the oil temperature cannot be accurately measured, the engine could be at risk of overheating or running with incorrect oil temperature data, potentially leading to short-term engine damage.

Can the vehicle be driven? Yes, but with caution. It’s advisable to address this issue promptly to prevent possible damage or inefficient operation. The vehicle might operate normally initially but could enter limp mode or show decreased performance if the problem worsens.

Symptoms of trouble code B1387

Typically, a vehicle with this code may display various symptoms, sometimes subtle, depending on how the ECU manages incomplete or incorrect information. Common symptoms include:

• Illumination of the Check Engine Light or other warning indicators
• Inconsistent or faulty oil temperature readings on the vehicle’s display
• Engine idle issues or rough running if the ECU reacts to faulty data
• Possible limp mode activation to protect the engine
• Fuel economy may decrease due to recalibrations based on erroneous data
• In some cases, no noticeable symptoms, but the code is stored in the ECU

Most likely causes of trouble code B1387

The presence of the B1387 code usually points toward issues in the oil temperature sensor circuit. Here are the most common causes, ranked from most to least likely:

1. Open or broken wiring in the sensor circuit, such as a disconnected or frayed wire.
2. Damaged or faulty oil temperature sensor that no longer provides a signal.
3. Corrosion or poor connection at the sensor connector, leading to signal interruption.
4. Problems with the ECU or its wiring, although less common, especially if other sensors are affected.
5. Short circuit to ground or power in the sensor circuit, causing false open circuit detection.

How to diagnose trouble code B1387

Diagnosing this code requires a systematic approach to eliminate possible causes. Here are general, non-manufacturer-specific steps to follow:

1. Visually inspect the wiring harness connected to the oil temperature sensor for obvious damage, corrosion, or disconnection.
2. Check the connector for signs of corrosion, loose fit, or damage. Reconnect properly if needed.
3. Test the sensor’s electrical circuit using a multimeter to check for continuity and proper resistance readings at various temperatures.
4. Use a scan tool or data reader to monitor live data for the oil temperature sensor to verify if the sensor is providing reasonable readings.
5. Perform a wiring continuity test between the sensor connector and the ECU to ensure there are no breaks in the wiring.
6. Test the sensor operating voltage and ground circuit to confirm proper power supply and grounding.

Possible repairs for trouble code B1387

Depending on the identified cause during diagnosis, repairs may vary from simple to complex. Here are potential fixes:

• Replacing a damaged wiring harness or repairing frayed or broken wires. (Basic repair, DIY-friendly if familiar with automotive wiring)
• Replacing the faulty oil temperature sensor if found defective. (Usually straightforward, professional installation recommended)
• Cleaning or re-seating the sensor connection to restore proper contact. (Basic, DIY approach)
• Verifying and repairing ECU wiring issues if suspected, which is a more advanced repair requiring professional diagnostics. (Professional service recommended)
• Addressing shorts or open circuits in the circuit wiring, if identified during testing.

Vehicles commonly associated with trouble code B1387 in Europe

This code is generally observed across various makes and models, particularly in vehicles with age or high mileage. While specific data is limited, common vehicles include:

Volkswagen and Audi: Many models within the Volkswagen Group rely on oil temperature sensors, and issues can surface in models like Golf, Passat, Audi A3, and A4.

Ford: Certain Ford models utilizing OBD-II systems may register similar circuit open codes related to oil temperature or related sensors.

Toyota, Honda, and Nissan: These brands sometimes report similar circuit issues, especially in older vehicles or those with sensor wiring problems.

Frequent mistakes with trouble code B1387

When diagnosing or repairing this issue, some errors can hinder proper resolution. Be mindful of the following:

• Assuming the sensor itself is always faulty without testing wiring or connections first.
• Ignoring visual inspection—damage or corrosion in wiring is a common cause that can be overlooked.
• Using incompatible or poor-quality replacement parts, which might fail prematurely.
• Neglecting to clear codes after repairs to verify if the problem reappears.
• Overlooking other related sensors or circuits that could contribute to the issue.

FAQ — trouble code B1387

Can this code disappear on its own? In most cases, no. The physical circuit issue will remain until the wiring, connector, or sensor is properly repaired or replaced. Clearing the code without fixing the root cause will likely lead to its return.

Can I keep driving? If the check engine light is on, it is generally safe to continue driving temporarily; however, you should have the issue diagnosed and repaired promptly. Prolonged operation with unresolved sensor problems could lead to engine performance issues or damage.

Why does the code return after clearing? Because the underlying circuit problem—such as broken wiring or a faulty sensor—has not been fixed. The ECU continuously monitors the circuit, and as soon as it detects the open circuit again, the code reappears.