A cooling system fault usually needs a check soon; if the temperature warning comes on, stop when safe and switch off the engine.
Trouble codes · P0118
P0118 meaning
Engine Coolant Temperature Sensor 1 Circuit High
The same first verdict Car Assist shows from this code alone, before a diagnosis. The code does not tell the app whether the warning light is flashing.
What this code doesn’t tell you
A code says where the car noticed a problem. It does not prove which part failed, whether the fault is still present, or what repair this car needs. The engine, other codes, freeze frame and live readings matter.
Usual causes, most likely first
The order is a starting point across cars; the exact engine and its readings can change it.
- Open coolant sensor wire or loose connector
- Failed coolant temperature sensor
- Poor electrical connection at the engine computer
What you can check
Usually a cold-engine visual check of the sensor connector is enough for an owner; have wiring damage or an implausible reading checked. Usually a temperature warning needs a stop when safe and the engine switched off.
Words the car uses
- Stored codes
- Faults the car has confirmed and saved. They help explain a check-engine light, but a code alone does not prove which part needs replacing.
- Freeze frame
- A snapshot of the engine's readings when a fault was recorded. It helps show the conditions that caused the fault, even if the car now seems fine.
- Readiness monitors
- The car's own checks of its emissions systems. An unfinished check means the car has not tested that system yet, so a clean code scan may miss a fault.
- Coolant
- The liquid that carries heat away from the engine. Its temperature helps show whether the engine warms up properly. An overheating warning usually needs a stop when safe and the engine switched off.
- Battery and ECU volts
- The electrical supply measured at the adapter or a car computer (ECU). Low readings can explain starting problems or unreliable diagnostic connections.
Find out what’s causing yours
Car Assist reads your car through an OBD-II adapter and your iPhone. Its assistant uses the codes, freeze frame and live readings to work through the likely cause with you.