Skip to content

P0187 – Fuel Temperature Sensor B Circuit Low Input (OBD2)

P0187 means "Fuel Temperature Sensor B Circuit Low Input". The voltage the control unit measures in the fuel composition / fuel temperature sensor circuit is below the permitted minimum. For a sensor this usually means the signal wire is shorted to ground or the reference voltage is missing; for an actuator, that its control wire is shorted to ground.

Last updated

P0187 quick summary

Fault codeP0187
MeaningFuel Temperature Sensor B Circuit Low Input
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityLow
Can I drive?Yes, in most cases. Power or starting may be slightly affected. If P0168 (fuel temperature too high) appears, avoid running the tank very low and have the fuel cooling checked.
Repair cost€20 – €400

How fuel composition and fuel temperature sensors work

These sensors tell the engine control unit the fuel's temperature and, on flex-fuel vehicles, its ethanol content, so it can correct injection quantity and timing.

Fuel temperature sensors are mostly used on diesels and some direct-injection engines: warm fuel is less dense, so the control unit adjusts the injected quantity. Flex-fuel vehicles use a fuel composition sensor that measures the ethanol percentage and fuel temperature in the supply line.

Codes in this group cover the sensors' electrical circuits and performance, an engine fuel temperature that is too high (P0168) and incorrect fuel composition (P0169). Very hot fuel can be caused by a faulty fuel cooler or by running the tank very low in hot weather.

A faulty fuel temperature signal usually causes mild symptoms – slightly reduced power or harder starting – while a wrong ethanol reading on a flex-fuel car can cause hard starting and poor running.

On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 16571 (P0187). Both numbers mean the same fault.

Symptoms of P0187

  • Check Engine light on
  • Slightly reduced power
  • Harder hot or cold starting
  • Higher fuel consumption
  • Often no noticeable symptoms

Most common causes of P0187 (most likely first)

Mechanic's Pro Tip

On diesels with P0168, check injector return flow: worn injectors that leak a lot of fuel back to the tank heat up the fuel – replacing the temperature sensor will not cure that.

  1. 1.Signal or control wire shorted to ground

    Most likely

    Look for chafed insulation where the harness touches the engine, exhaust brackets or body edges.

  2. 2.Missing 5 V reference or supply voltage

    An open reference wire or a shorted sensor elsewhere on the same reference circuit can pull it down.

  3. 3.Internal short in the fuel composition / fuel temperature sensor

  4. 4.Failed fuel temperature or composition sensor

  5. 5.Damaged wiring or corroded connector

  6. 6.Fuel genuinely too hot (P0168)

    Faulty fuel cooler, very low fuel level in hot weather or an excessive return flow from leaking injectors.

  7. 7.Wrong or contaminated fuel (P0169)

    For example water in the fuel or a wrong ethanol blend.

Step-by-step diagnostic guide

  1. 1

    Read codes and live data

    Read all codes and compare the fuel temperature in live data with coolant and intake air temperature on a cold engine.

  2. 2

    Measure the signal voltage

    With the ignition on and the fuel composition / fuel temperature sensor plugged in, back-probe the signal wire. Then unplug it and check the reference/supply and ground wires separately.

    Multimeter: Signal near 0 V = short to ground or no reference. Reference wire: about 5 V with ignition on. Signal wire to ground with connector unplugged: no continuity.

  3. 3

    Measure the sensor

    Measure resistance (thermistor) at a known temperature or check the frequency signal of a composition sensor.

    Multimeter: Thermistor sensors: resistance falls as temperature rises; compare with the specification table.

  4. 4

    Check wiring

    Check the reference, ground and signal wires for opens and shorts.

  5. 5

    Check fuel quality and cooling

    Check for water in the fuel, the correct fuel type and – for P0168 – the fuel cooler and return flow.

  6. 6

    Replace and verify

    Replace the sensor or fix the cause and clear codes.

Frequently asked questions

Can I keep driving with P0187?

Yes, in most cases. Power or starting may be slightly affected. If P0168 (fuel temperature too high) appears, avoid running the tank very low and have the fuel cooling checked.

How much does it cost to fix P0187?

Typical repair costs are 20 € – 400 €, depending on the cause and the vehicle. The most common fixes are: signal or control wire shorted to ground; missing 5 V reference or supply voltage; internal short in the fuel composition / fuel temperature sensor. Always confirm the cause with the tests above before buying parts.

What does P0169 incorrect fuel composition mean?

The control unit measured a fuel composition it does not expect – usually on flex-fuel vehicles with a wrong ethanol content, or with water or contamination in the fuel.

Why does fuel temperature matter?

Warm fuel is less dense, so the same injection time delivers less fuel. The control unit corrects for this using the fuel temperature sensor.

What is the difference between P0187 and similar codes?

P0187 belongs to a group of codes for the same component that differ in the type or location of the fault: P0183 – Fuel Temperature Sensor A Circuit High Input; P0184 – Fuel Temperature Sensor A Circuit Intermittent; P0185 – Fuel Temperature Sensor B Circuit Malfunction; P0186 – Fuel Temperature Sensor B Circuit Range/Performance; P0188 – Fuel Temperature Sensor B Circuit High Input; P0189 – Fuel Temperature Sensor B Circuit Intermittent. The tests on this page apply to the whole group; the type of fault tells you where to start.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.