All codes
Engine Coolant Temperature Sensor High Input
Fix the P0118 coolant temperature sensor high-input code, which the ECM reads as an impossibly cold engine.
What you may notice
Symptoms
- 01Check engine light on
- 02Poor fuel economy
- 03Hard starting when warm
- 04Cooling fan behavior incorrect
- 05Black smoke from over-fueling
Where to look first
Common causes
- 01Failed coolant temperature sensor
- 02Open in the sensor signal wire
- 03Poor connector contact or corrosion
- 04Loss of sensor ground
Step by step
What to check and repair
- 01Compare reported coolant temp to actual with a scan tool
- 02Inspect the connector and wiring for opens
- 03Check the sensor ground circuit
- 04Replace the coolant temperature sensor if faulty
What Does P0118 Mean?
The P0118 code indicates the engine coolant temperature (ECT) sensor signal voltage is too high, which the ECM interprets as an extremely cold engine. This throws off fuel mixture and cooling fan control.
Why the Engine Runs Rich
If the ECM thinks the engine is freezing cold, it adds extra fuel. That means P0118 often comes with poor fuel economy and hard hot restarts even when the engine is actually warm.
How AI4Car Helps
AI4Car displays the reported coolant temperature live. If it reads far colder than reality after the engine warms up, the sensor or its wiring is the problem.