Open circuit in the signal wire between Fuel Temperature Sensor B and the ECM, often due to a broken wire or corroded connector; Failed fuel temperature sensor (thermistor) with an internal open circuit; Poor electrical connection at the sensor or ECM connector, including backed-out pins or water intrusion; High resistance in the ground circuit for the sensor, causing the signal voltage to float high; Damaged or chafed wiring harness shorting the signal circuit to a higher voltage source; Faulty ECM driver or internal pull-up resistor, though this is the least likely cause

DTC codes / P01xx · Fuel and air metering / P0188

P0188Fuel Temperature Sensor B Circuit High

Q: What does code P0188 mean?

Fuel Temperature Sensor B Circuit High. P0188 means the engine control module (ECM) has detected an abnormally high voltage on the signal circuit for Fuel Temperature Sensor B, which is typically a thermistor whose resistance drops as fuel temperature rises. The ECM interprets this high voltage as an open circuit or a sensor reporting an impossibly cold fuel temperature, so it flags the circuit as faulty.

P0188 means the engine control module (ECM) has detected an abnormally high voltage on the signal circuit for Fuel Temperature Sensor B, which is typically a thermistor whose resistance drops as fuel temperature rises. The ECM interprets this high voltage as an open circuit or a sensor reporting an impossibly cold fuel temperature, so it flags the circuit as faulty.

SystemPowertrain

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the malfunction indicator lamp (MIL) on the dashboard
Often no symptoms besides the warning light, especially in mild weather
Rough idle or hesitation when the engine is cold, because fuel temperature is used for cold-start enrichment
Slightly reduced fuel economy or poor driveability during warm-up
Hard starting or extended cranking in cold ambient temperatures
In rare cases, a default value is substituted and the engine runs normally with no noticeable change

Common causes, most likely first

Open circuit in the signal wire between Fuel Temperature Sensor B and the ECM, often due to a broken wire or corroded connector
Failed fuel temperature sensor (thermistor) with an internal open circuit
Poor electrical connection at the sensor or ECM connector, including backed-out pins or water intrusion
High resistance in the ground circuit for the sensor, causing the signal voltage to float high
Damaged or chafed wiring harness shorting the signal circuit to a higher voltage source
Faulty ECM driver or internal pull-up resistor, though this is the least likely cause

How to diagnose and fix it

Scan all modules and record freeze-frame data to confirm P0188 is the only fuel temperature-related code and note the reported sensor voltage
Inspect the sensor connector and wiring for corrosion, loose pins, or obvious damage, and repair as needed
Measure the sensor resistance with a multimeter and compare it to the manufacturer's temperature-resistance chart; replace the sensor if it is open or out of spec
Backprobe the signal circuit at the ECM connector and check for an open or high-resistance wire between the sensor and ECM
Check the sensor ground circuit for excessive resistance and repair any corroded or broken ground points
Clear the code and perform a road test with live data to verify the fuel temperature reading changes smoothly and the code does not return
If all wiring and the sensor test good, follow the manufacturer's diagnostic flow for an internal ECM fault before replacing the ECM

What a high fuel temp signal really means

A high signal voltage almost always indicates an open circuit or a disconnected sensor, not a genuinely hot fuel condition, so do not chase fuel cooling problems first.
Many vehicles use Fuel Temperature Sensor B as part of a combined fuel rail temperature and pressure sensor, so a failed sensor may also set pressure-related codes that lead technicians away from the real fault.
The ECM may substitute a default fuel temperature value and run the engine almost normally, which is why this code often appears with no driveability complaint at all.
Corrosion inside the sensor connector is a frequent cause that a simple visual inspection misses; always wiggle-test the harness while watching live data.
On some applications, the fuel temperature sensor shares a reference voltage or ground with other sensors, so a fault in that shared circuit can set P0188 alongside codes for those sensors.

Can I keep driving with P0188?

The vehicle is generally safe to drive with P0188 because the ECM substitutes a default fuel temperature and the engine remains driveable, but avoid heavy loads or long trips until the circuit is repaired. If you notice rough running, hard starting, or the engine enters limp mode, have it diagnosed promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.