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P0185 – Fuel Temperature Sensor B Circuit Malfunction (OBD2)

P0185 means "Fuel Temperature Sensor B Circuit Malfunction". The control unit has detected a fault in the electrical circuit of the fuel composition / fuel temperature sensor: the signal or control current is missing or outside the expected window. The code does not say whether the value is too high or too low, so the wiring and the component itself both have to be checked.

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P0185 quick summary

Fault codeP0185
MeaningFuel Temperature Sensor B Circuit Malfunction
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 16569 (P0185). Both numbers mean the same fault.

Symptoms of P0185

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

Most common causes of P0185 (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.Damaged wire or loose, corroded connector at the fuel composition / fuel temperature sensor

    Most likely

    Green or white corrosion, pushed-back pins and chafed insulation near hot or moving parts are the most common findings.

  2. 2.Faulty fuel composition / fuel temperature sensor

    An internal break or short in the component itself.

  3. 3.Blown fuse or missing supply voltage

    If several codes appeared at the same time, check the shared fuse, relay or ground point first.

  4. 4.Fuel genuinely too hot (P0168)

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

  5. 5.Wrong or contaminated fuel (P0169)

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

  6. 6.5 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 the circuit with a multimeter

    With the ignition off, unplug the fuel composition / fuel temperature sensor and the control unit connector (or back-probe), then check each wire between them for continuity and for shorts to ground and to battery voltage. Compare the component's resistance or supply voltage with the value in the repair manual.

    Multimeter: Wire continuity: below about 1 Ω. Wire to ground with both connectors unplugged: no continuity. Supply/reference with ignition on: usually 5 V for sensors, battery voltage for actuators.

  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 P0185?

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 P0185?

Typical repair costs are 20 € – 400 €, depending on the cause and the vehicle. The most common fixes are: damaged wire or loose, corroded connector at the fuel composition / fuel temperature sensor; faulty fuel composition / fuel temperature sensor; blown fuse or missing supply voltage. 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 P0185 and similar codes?

P0185 belongs to a group of codes for the same component that differ in the type or location of the fault: P0182 – Fuel Temperature Sensor A Circuit low Input; P0183 – Fuel Temperature Sensor A Circuit High Input; P0184 – Fuel Temperature Sensor A Circuit Intermittent; P0186 – Fuel Temperature Sensor B Circuit Range/Performance; P0187 – Fuel Temperature Sensor B Circuit Low Input; P0188 – Fuel Temperature Sensor B Circuit High Input. 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.