P0118Engine Coolant Temperature Sensor 1 Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- The engine coolant temperature sensor 1 is an NTC thermistor: the control module feeds 5 V through a resistor, and as the coolant warms the resistance and signal voltage fall. Its value drives cold-start enrichment, idle speed, ignition timing, the radiator fan and the release of closed-loop mixture control. Some Ford engines measure cylinder head temperature instead and calculate a coolant value from it. P0118 means the signal voltage sits near the 5 V reference, so the sensor would report about −40 °C. Typical causes are an unplugged or corroded connector, a broken signal or sensor ground wire, an open sensor or a short to voltage. Limits: GM above 134 kilohms (only after 10 s running, so genuine cold is not misread), Ford petrol above 4.96 V for 5 s, Ford diesel above 4.91 V, GM/Saab below −39 °C for 4 s. Without a substitute strategy the mixture would be far too rich; GM/Saab run the fan and switch off the A/C. On Ford engines with a head temperature sensor the equivalent is P1289.
- What you may notice
- Check engine light on
- Radiator fan runs constantly
- Temperature gauge stays cold
- Rich mixture, higher consumption, possibly black smoke or fuel smell
- Raised idle speed
- Likely causes
- LikelyConnector unplugged or corroded, contact open
- PossibleBroken signal or sensor ground wire
- PossibleSensor open internally
- RareSignal wire shorted to 5 V or battery voltage
- RareEngine control module faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €20 – €150
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.