Faulty or drifting fuel temperature sensor B; Corroded, loose or damaged connector terminals at the sensor, giving high resistance; Damaged wiring, chafing or high resistance in the signal or reference ground circuit; Sensor exposed to unusual heat, for example from nearby exhaust components or a poor fuel return, giving a genuine but implausible reading; Other fault affecting the shared 5 volt reference or ground supply; Fault in the engine control unit.

P0186

Fuel Temperature Sensor B Circuit Range/Performance.

Generic
Powertrain
Generic code
Low severity

How this code is built

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

What it means

P0186 means the engine control unit has found that the signal from fuel temperature sensor B is not plausible, even though the circuit is not necessarily open or shorted. It usually sets when the reading is stuck, drifts, or disagrees with other temperatures such as coolant and intake air after a long cold soak. Which sensor is 'B' and where it sits (fuel rail, fuel line, return line or pump module) depends on the vehicle.

Symptoms

Engine warning light on
Hard or extended cranking when starting, especially hot or cold
Slightly rough running or hesitation
Poor fuel economy
Reduced power if the control unit applies a fallback fuel temperature value
No obvious symptoms in some cases

Possible causes

Faulty or drifting fuel temperature sensor Blikely
Corroded, loose or damaged connector terminals at the sensor, giving high resistancelikely
Damaged wiring, chafing or high resistance in the signal or reference ground circuitpossible
Sensor exposed to unusual heat, for example from nearby exhaust components or a poor fuel return, giving a genuine but implausible readingpossible
Other fault affecting the shared 5 volt reference or ground supplypossible
Fault in the engine control unitrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting engine temperature and fuel temperature at the time of setting.
Check for related codes on other temperature sensors or the sensor reference voltage, and deal with those first.
Inspect the sensor, connector and wiring for damage, corrosion, moisture, heat damage and chafing.
After a long cold soak, compare the live fuel temperature reading with coolant and intake air temperature; they should be close.
Watch the live fuel temperature as the engine warms up; look for a stuck, jumping or implausibly slow-changing value.
Check the sensor resistance against the manufacturer's temperature table, and test the signal and ground circuits for resistance, shorts and open circuits.
Check the sensor's location and surroundings for heat sources or fuel system faults, following the model-specific procedure.
Clear the code and road test to confirm it does not return.

How to fix

Replace the fuel temperature sensor if its readings are out of specification or unstable.
Clean or repair the connector terminals, or replace the connector if it is damaged or corroded.
Repair or replace damaged wiring in the signal or ground circuit.
Correct any heat source or fuel system issue causing the genuine temperature reading to be implausible.
Rectify any reference voltage or ground fault affecting the sensor circuit.
Diagnose and, only if proven faulty, replace or repair the control unit.

Can I keep driving?

Low severity

The car can normally be driven while you book it in, as the control unit usually uses a default fuel temperature value. If you notice hard starting or loss of power, have it checked sooner.

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