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P0188 – Fuel Temperature Sensor B Circuit High Input (OBD2)

P0188 means "Fuel Temperature Sensor B Circuit High Input". The voltage in the fuel composition / fuel temperature sensor circuit is above the permitted maximum. For most sensors this points to an open signal or ground wire – the signal "floats" up to the reference voltage – or to a short to voltage.

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P0188 quick summary

Fault codeP0188
MeaningFuel Temperature Sensor B Circuit High 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 16572 (P0188). Both numbers mean the same fault.

Symptoms of P0188

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

Most common causes of P0188 (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.Open circuit in the signal or ground wire

    Most likely

    A loose ground connection is a very common cause.

  2. 2.Signal wire shorted to the 5 V reference or battery voltage

  3. 3.Faulty fuel composition / fuel temperature sensor

  4. 4.Damaged wiring or corroded connector

  5. 5.Fuel genuinely too hot (P0168)

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

  6. 6.Wrong or contaminated fuel (P0169)

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

  7. 7.5 V reference or ground problem

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

    Check signal and ground

    With the ignition on and the fuel composition / fuel temperature sensor plugged in, back-probe the signal and ground wires. A signal stuck at reference or battery voltage points to an open ground/signal wire or a short to voltage.

    Multimeter: Ground wire to battery negative: below about 0.1 V. Signal stuck at about 5 V (or 12 V) = open or short to voltage.

  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 P0188?

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 P0188?

Typical repair costs are 20 € – 400 €, depending on the cause and the vehicle. The most common fixes are: open circuit in the signal or ground wire; signal wire shorted to the 5 V reference or battery voltage; faulty 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 P0188 and similar codes?

P0188 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; P0187 – Fuel Temperature Sensor B Circuit Low 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.