P0187
UniversalFuel Temperature Sensor B Circuit Low Input
Medium SeverityThe Engine Control Module (ECM) detects an abnormally low voltage signal from the Fuel Temperature Sensor B circuit. This indicates a potential electrical problem with the sensor or its wiring, or a sensor malfunction itself. This can lead to inaccurate fuel mixture calculations, resulting in issues like poor fuel economy, rough idling, or difficulty starting the vehicle.
⚠️ Before You Begin (Safety First)
Always exercise caution when working on a vehicle's fuel system. Fuel is highly flammable, so ensure adequate ventilation and have a fire extinguisher nearby. Before performing any electrical work, always disconnect the negative battery cable to prevent accidental shorts or electrical shocks.
Common Symptoms
- Illuminated Check Engine Light
- Poor fuel economy
- Rough idling
- Hard starting or no start condition
- Reduced engine performance or acceleration
- Engine stalling
Common Causes
- Faulty Fuel Temperature Sensor B
- Open or short circuit in the sensor's wiring harness
- Corroded or loose electrical connections at the sensor or ECM
- Faulty Engine Control Module (ECM) (less common)
- Short to ground in the sensor circuit
Frequently reported on: All Makes
Diagnostic Steps
- Connect an OBD-II scanner to confirm the P0187 code and check for any other related codes.
- Visually inspect the wiring harness and connectors for the Fuel Temperature Sensor B for any signs of damage, fraying, corrosion, or loose connections. Ensure they are securely plugged in.
- Using a digital multimeter, test the resistance of the Fuel Temperature Sensor B. Compare readings to manufacturer specifications, which typically change with temperature. An open or short circuit within the sensor indicates a fault.
- Check the voltage supply to the sensor and signal return wire for proper readings. A 'low input' often points to a short to ground or an open circuit preventing proper voltage.
- If the sensor tests bad or wiring issues are found, replace the faulty component. Clear the DTCs and perform a test drive to see if the code returns.
👨🔧 When to Call a Professional
If after inspecting the wiring, connectors, and performing basic multimeter tests on the sensor, the P0187 code persists, or if you lack the specialized diagnostic tools and experience for in-depth electrical circuit testing, it is highly recommended to consult a professional mechanic. This code often points to a complex electrical fault that requires expert diagnosis.
Commonly Asked Questions
What specifically does P0187 mean for my car?
P0187 indicates that your car's computer (ECM) is receiving an unusually low voltage signal from the Fuel Temperature Sensor B, suggesting an electrical problem within that circuit or a faulty sensor.
Can I continue driving my car with a P0187 code?
While you might be able to drive, it's not recommended for extended periods. The incorrect fuel temperature readings can lead to poor engine performance, reduced fuel economy, increased emissions, and potential damage to other engine components over time. It's best to address it promptly.
Where is the Fuel Temperature Sensor B usually located?
The exact location of Fuel Temperature Sensor B can vary significantly by vehicle make and model. It's typically found within the fuel tank, integrated into the fuel pump assembly, or sometimes in the fuel rail or fuel line itself.
How can I test the Fuel Temperature Sensor B?
You can test it using a digital multimeter. With the sensor disconnected, measure its resistance across the terminals. Compare this reading to the manufacturer's specifications, often found in a service manual. The resistance should change predictably with temperature.
What should I do if replacing the sensor doesn't fix the P0187 code?
If a new sensor doesn't resolve the issue, the problem likely lies in the wiring harness or connectors. You'll need to meticulously check for opens, shorts, or poor connections in the circuit leading to and from the sensor. In rare cases, a faulty ECM could also be the cause.