Fuel and air

P0186 — Fuel Temperature Sensor B Circuit Range/Performance

Severity: low Safe to drive

What P0186 means

The engine control module constantly reads fuel temperature sensor B and compares it with what it expects. Fuel temperature affects fuel density, so the ECM uses it to adjust fueling. P0186 is set when the signal falls outside the expected range or doesn't agree with other data, such as coolant or air temperature on a cold-soaked engine.

Symptoms

  • Check Engine Light on
  • Rough cold starts or hesitation
  • Reduced fuel economy
  • Erratic fuel trim values
  • Occasionally unstable idle or sluggish performance

Possible causes

  1. Failed fuel temperature sensor B
  2. Damaged wiring: open, short, or corroded terminals
  3. Poor connection at the sensor connector
  4. ECM/PCM fault or calibration issue (uncommon)
  5. Fuel system condition affecting sensor readings

How to diagnose

  1. Read all codes and freeze frame data and look for related fuel system codes
  2. With a scan tool, compare fuel temperature to coolant and intake air temperature on a cold engine; they should be close
  3. Inspect the sensor, connector, and harness for damage, moisture, corrosion, and chafing
  4. Check reference voltage and ground at the sensor connector with a multimeter
  5. Measure the sensor resistance and compare it to the spec for your vehicle
  6. Test the wiring to the ECM for opens and shorts to ground or power
  7. If the sensor and wiring are good, check the ECM and look for software updates

Common fixes

  • Replace fuel temperature sensor B
  • Repair or replace damaged wiring and connectors
  • Clean terminals and eliminate moisture intrusion
  • Reflash or replace the ECM if confirmed faulty

Questions and answers

What does P0186 mean?

The ECM is getting a signal from fuel temperature sensor B that is out of range or doesn't match other data. The sensor or its wiring is the most common culprit.

Can I drive with P0186?

Usually yes for short trips. Rough cold starts and higher fuel use are possible, so get it checked soon.

How do I fix P0186?

Start with the connector and wiring, then test the sensor with a multimeter. Replacing the sensor or repairing the wiring 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.