P0187
UniversalFuel Temperature Sensor B Circuit Low Input
The engine computer has detected a low electrical input in the circuit for fuel temperature sensor B. This sensor reports fuel temperature so the computer can use that information in engine control. The code identifies a circuit condition, not proof that the sensor itself has failed. The vehicle may run normally, or engine operation and fuel economy may be affected, depending on the vehicle.
⚠️ Before You Begin (Safety First)
If you notice a fuel leak, strong fuel smell, smoke, or severe engine stalling, stop driving when safe and have the vehicle inspected. Avoid opening fuel lines or working near leaking fuel. Exact diagnosis and procedures depend on the vehicle.
Common Symptoms
- The check-engine light may be on, while the vehicle otherwise appears to run normally.
- Engine performance or fuel economy may change if the computer's fuel-temperature information affects engine control.
- Starting or running may be affected in some vehicles, but this code can also occur without noticeable symptoms.
Common Causes
- Fuel temperature sensor B may be electrically faulty.
- A damaged, corroded, loose, or poorly connected plug or wire may cause a low circuit input.
- A short to ground or another wiring fault may pull the circuit input low.
- A problem in the computer's sensor circuit is possible and should be considered only after appropriate checks.
Diagnostic Steps
- Note whether the check-engine light is steady or flashing and watch for poor running, stalling, fuel smell, or leaks; stop driving if there is a leak or severe running problem.
- With the vehicle off and cool, visually inspect accessible wiring and connectors for damage, looseness, corrosion, or signs of fuel leakage. Do not disconnect fuel lines.
- If a scan tool is available, record the code and check whether fuel-temperature readings appear plausible or remain fixed. Interpret the data using information for the specific vehicle.
- If the code returns or wiring damage is not obvious, arrange vehicle-specific electrical diagnosis rather than replacing the sensor based on the code alone.
When to Call a Professional
A technician can compare sensor B live data with other available temperature readings, inspect the circuit using the vehicle-specific wiring information, and test the sensor and wiring as appropriate. The low input may result from a sensor fault, wiring or connector damage, or another circuit problem, so confirm the cause before replacing parts.
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Commonly Asked Questions
Does P0187 prove that fuel temperature sensor B needs replacement?
No. It reports a low electrical input in the sensor B circuit. The sensor, wiring, connector, or another part of the circuit could be responsible.
What does “circuit low input” mean?
The engine computer detected an input voltage lower than expected for that circuit. It does not by itself identify why the input is low or establish the actual fuel temperature.
Can I keep driving with this code?
If the vehicle runs normally and there is no fuel smell or leak, arrange diagnosis soon. Stop driving when safe if you notice a leak, strong fuel smell, severe stalling, or another serious running problem.
How is P0187 diagnosed?
Diagnosis typically starts with scan data and inspection of the sensor circuit, then uses vehicle-specific wiring information to test the sensor and wiring. The correct procedure varies by model, year, and engine.
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