Fuel temperature sensor B signal wire shorted to earth or to another low-voltage wire; Faulty fuel temperature sensor with internal short or very low resistance; Damaged, corroded or contaminated sensor connector causing a low signal voltage; Chafed or water-damaged wiring harness near the fuel rail, filter or tank; Sensor reference supply or earth circuit fault; Fault inside the engine control unit.

P0187

Fuel Temperature Sensor B Circuit Low.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
87: FaultThe specific fault in that area

What it means

P0187 means the engine control unit has detected the signal voltage from fuel temperature sensor B is lower than expected, which it reads as an implausibly high fuel temperature. The fault is set when the sensor circuit voltage stays below the calibrated limit for long enough. Which sensor is 'B' and where it sits depends on the vehicle and fuel system.

Symptoms

Engine warning light on
Hard or extended cranking when starting, particularly when hot
Rough running or hesitation under load
Poor fuel economy
Reduced power if the control unit applies a fallback strategy
Possible fuel temperature related corrections or default values in live data

Possible causes

Fuel temperature sensor B signal wire shorted to earth or to another low-voltage wirelikely
Faulty fuel temperature sensor with internal short or very low resistancelikely
Damaged, corroded or contaminated sensor connector causing a low signal voltagepossible
Chafed or water-damaged wiring harness near the fuel rail, filter or tankpossible
Sensor reference supply or earth circuit faultpossible
Fault inside the engine control unitrare

How to diagnose

Read the stored and pending codes and freeze frame data, and note whether other sensor or circuit codes are present.
Check live data for fuel temperature B with the engine cold and compare it with ambient or coolant temperature; an implausibly high reading points to a low-voltage circuit.
Inspect the sensor, connector and harness for chafing, corrosion, moisture, heat damage and poor pin tension.
With the sensor unplugged, see if the reading changes to an open-circuit value; if it does, suspect the sensor, and if it does not, suspect the wiring or control unit.
Measure the sensor resistance and compare it with the manufacturer's temperature table for that model.
Check the wiring for a short to earth, and test the reference supply and earth at the connector against the wiring diagram.
Wiggle test the harness while watching live data for sudden changes.
Confirm the location and function of sensor B for the specific model and engine before replacing parts.

How to fix

Repair or replace damaged wiring that is shorted to earth, following the wiring diagram.
Clean, repair or replace a corroded or damaged connector and its terminals.
Replace the fuel temperature sensor B if its resistance or response is out of specification.
Restore the sensor reference supply or earth circuit if it is faulty.
Only after all other tests, and following manufacturer diagnostics, consider repair or replacement of the control unit.

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but book it in soon because hot starting and performance can suffer and the control unit may be relying on default fuel temperature values. Stop driving if it runs very poorly or loses power.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.