P0187 Fuel Temperature Sensor B Circuit Low Input

P0187 indicates fuel temperature sensor B circuit low. The signal is below expected voltage or reporting an unrealistically cold value.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not diagnose fuel pressure or composition faults until the low sensor B circuit is corrected.

Symptoms of P0187

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0187

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Measure fuel temperature B signal voltage, reference, ground, and sensor resistance while checking for short-to-ground faults.
Inspect connector corrosion, harness routing, fuel contamination at terminals, shared reference faults, and sensor mounting.
Compare the low reading with fuel temperature A, ambient, coolant, and intake temperature after cold soak.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.