Fuel and air

P0188 — Fuel Temperature Sensor 'B' Circuit High Input

Severity: medium Safe to drive

What P0188 means

The engine control module constantly reads the voltage from fuel temperature sensor 'B'. It is a thermistor: as fuel warms up, its resistance drops and the signal voltage falls. P0188 sets when the voltage stays above the expected range, usually from an open circuit, a poor connection, a short to power or a failed sensor. The ECM then has no reliable fuel temperature reading.

Symptoms

  • Check Engine Light on
  • Reduced fuel economy
  • Rough idle
  • Hard starting
  • Hesitation or occasional stalling

Possible causes

  1. Failed fuel temperature sensor 'B' (internal open circuit)
  2. Corroded or damaged sensor connector terminals
  3. Open signal or ground wire
  4. Signal wire shorted to voltage
  5. Faulty ECM input circuit
  6. Rarely, ECM software issue

How to diagnose

  1. Scan all codes and freeze frame data, then clear P0188 and see if it returns
  2. Check the fuel temperature reading on a scan tool: a value stuck at an extreme suggests an open or short
  3. Inspect the sensor connector and harness for corrosion, moisture, chafing or bent pins
  4. Unplug the sensor and check for reference voltage (typically about 5 V) and ground per the wiring diagram
  5. Measure sensor resistance and compare it to the spec at a known temperature
  6. Test the signal wire to the ECM for opens and shorts to voltage
  7. If wiring and sensor are good, check the ECM and look for a software update

Common fixes

  • Replace fuel temperature sensor 'B'
  • Repair or replace the damaged wiring harness
  • Clean or replace the connector and terminals
  • Reflash or replace the ECM (last resort)

Questions and answers

What does P0188 mean?

The ECM sees too high a voltage from the fuel temperature sensor 'B' circuit. It is most often caused by an open wire, a bad connection or a failed sensor.

Can I drive with P0188?

Usually yes for a short time, since the ECM uses a default value. Economy and drivability may suffer, so get it diagnosed soon.

How do I fix P0188?

Start with the sensor connector and wiring, then test the sensor with a multimeter. Repairing the harness or replacing the sensor fixes most cases.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.