Parts
$15–50
P0116 — Engine Coolant Temperature Sensor Range / Performance
CAUTIONIs it safe to drive? Drive with caution and watch your temperature gauge — if the gauge reads correctly but this code is set, the ECT sensor is lying to the ECU, which can cause rich running and elevated catalyst temperatures.
What P0116 means
The ECT sensor value doesn't match what the ECU expects given startup conditions, warmup rate, or comparison with IAT. The sensor may be stuck at a fixed value rather than tracking engine warm-up.
Most likely causes (in order)
- Faulty ECT sensor — most common, sensor sticks at a fixed resistance ($15–40)
- Air pocket in cooling system near the sensor causing false readings
- Thermostat stuck open (engine never reaches full operating temp, ECT reads too low)
- Corroded or intermittent connector
- Low coolant level exposing the sensor tip to air
Symptoms you might notice
- Poor fuel economy (ECU keeps adding cold-start enrichment)
- Rough running when warm
- Engine may never reach full operating temp
- Heater output may be poor if thermostat is also stuck open
What to check first
Watch live ECT data on a scan tool from a cold start — a good sensor will climb steadily from ambient to ~195–210°F within 5–10 minutes. A stuck sensor will plateau early or show no movement at all. Compare ECT to IAT at cold soak — they should match within 5–10°F if the car has sat overnight.
Repair cost & difficulty
Labor
0.3–0.7 hr
Difficulty
DIY-friendly