P0118: Engine coolant temperature sensor circuit high input
Drive carefully. Get it checked within a week or two.
Can I drive with P0118?
Yes, but drive carefully and get it checked soon. The computer thinks the engine is at -40°, running excessively rich and fouling spark plugs.
What does P0118 mean?
P0118 stands for Engine Coolant Temperature Circuit High Input.
Symptoms you may notice
- Cabin heater blows lukewarm or cool air in cold weather
- Dashboard temperature gauge stays near cold or fluctuates
- Radiator cooling fans running at high speed continuously
- Decreased gas mileage due to prolonged engine warm-up
How much does it cost to fix?
Repair costs for code P0118 depend on the specific underlying root cause, ranging from simple DIY checks to component replacement. The table below lists the most common causes and rough price ranges in USD:
- Unplugged or loose ECT sensor connector
- Broken wire or open circuit in ECT sensor harness
- Internal open circuit in the temperature sensor
- Severely corroded connector terminals
What to do next
- Check the wiring plug directly mounted to the thermostat housing or cylinder head.
- Measure resistance across the ECT sensor terminals with a digital multimeter.
- Jumper the connector with a fused wire to verify wiring continuity to the ECU.
Last updated: October 2026
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General guidance only, not a professional diagnosis. If the check-engine light is flashing, or the car is running rough, overheating or losing power, stop driving and get help.
About this code
When code P0118 registers, the computer detects high voltage resulting from an open circuit. Believing the engine is freezing cold, the ECU dumps excess fuel into the cylinders. This can cause black exhaust smoke, fouled spark plugs, and rough idling. Fixing the wiring or sensor prevents catalytic converter degradation.