Cooling system
P0118 — Engine Coolant Temperature Circuit High
The coolant temperature sensor signal is higher than normal, which the ECU reads as extremely cold coolant (usually an open circuit). It enriches the mixture and may not switch the fan on when needed.
Common causes
- Open circuit or broken sensor wire
- Faulty ECT sensor
- Loose or corroded connector
- Ground fault in the sensor circuit
- Engine control module fault (rare)
Symptoms
- Hard starting when warm
- Black smoke and high fuel use
- Cooling fan may not start
- Check engine light
How to check
- Check the ECT connector and wiring for an open circuit
- Read live ECT; a constant -40 deg C suggests an open circuit
- Measure the sensor resistance and compare it with the specification
- Replace the sensor if needed
Can you keep driving?
Be careful: if the fan may not run, the engine can overheat in traffic. Watch the real temperature gauge and repair it soon.
Related codes
Frequently asked questions
- What does P0118 mean?
- The ECT sensor circuit voltage is high, as if the engine were very cold, often because of an open circuit.
- Can P0118 cause overheating?
- It can, if the ECU does not turn on the cooling fan because it thinks the engine is cold.
General reference information. It does not replace a diagnosis on your own vehicle. The same code can have different causes depending on make, model year and engine; check the manufacturer's documentation or ask a technician with a scan tool.