Open circuit in the sensor signal or return wire, or a high-resistance connection; Corroded, loose or damaged connector at the fuel temperature sensor; Faulty fuel temperature sensor (internal open circuit); Signal wire shorted to a voltage supply or reference feed; Damaged wiring where it chafes, or has been affected by heat or fuel contamination; Fault inside the engine control unit or a related fuel control module.

P0188

Fuel Temperature Sensor B Circuit High.

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
88: FaultThe specific fault in that area

What it means

P0188 means the engine control unit has seen a signal voltage from fuel temperature sensor B that is higher than expected, which points to a circuit fault in that sensor's circuit. A high voltage usually corresponds to an open circuit, a short to voltage or a very low temperature reading that cannot be real. The control unit uses this sensor to correct fuel density and injection or pump control, so it may fall back on a default value.

Symptoms

Engine warning light on
Hard or extended cranking when starting, especially from cold or hot
Rough running or hesitation under load
Poor fuel economy
Reduced power or limp mode on some vehicles
Fuel temperature reading stuck at an extreme low value on a scan tool

Possible causes

Open circuit in the sensor signal or return wire, or a high-resistance connectionlikely
Corroded, loose or damaged connector at the fuel temperature sensorlikely
Faulty fuel temperature sensor (internal open circuit)likely
Signal wire shorted to a voltage supply or reference feedpossible
Damaged wiring where it chafes, or has been affected by heat or fuel contaminationpossible
Fault inside the engine control unit or a related fuel control modulerare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including engine temperature and whether it was a cold or hot start.
Check the live fuel temperature reading for sensor B; a stuck, implausibly cold or maximum-voltage value suggests an open or short to voltage.
Inspect the sensor, its connector and the wiring for damage, chafing, corrosion, fuel contamination or bent pins.
With the ignition on, unplug the sensor and check the live value; compare it with the manufacturer's expected behaviour for your model, as sensor location and wiring vary by engine.
Measure the sensor resistance and compare it with the manufacturer's temperature-resistance specification.
Check the reference voltage and ground at the connector against wiring diagram values.
Test the signal wire for continuity and for shorts to voltage or to other wires, with the control unit unplugged.
If the wiring and sensor are good, check for a control unit fault after confirming supply and ground, and check for any relevant manufacturer updates.

How to fix

Repair or replace damaged wiring, correcting any open circuit or short to voltage.
Clean or replace the corroded or damaged connector and terminals.
Replace the fuel temperature sensor if its resistance is out of specification.
Secure and reroute the loom away from heat and chafing points.
Repair or replace the control unit only once all other causes are ruled out and the fault is confirmed.
Clear the code and road test, then confirm the fuel temperature reading is plausible and the code does not return.

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but fix it soon, as incorrect fuel temperature data may affect starting, performance and economy. If it goes into limp mode or runs poorly, limit driving.

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