P0118 code meaning
Engine Coolant Temperature Sensor 1 Circuit High
Powertrain system Generic code P01xx codes Check engine light
What P0118 means
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 gasoline 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.
P0118 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 1.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0118
- 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
Common causes of P0118
- Most likelyConnector unplugged or corroded, contact open
- PossibleBroken signal or sensor ground wire
- PossibleSensor open internally
- Less likelySignal wire shorted to 5 V or battery voltage
- Less likelyEngine control module faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Engine coolant temperature sensorEngine coolant temperature sensor wiring
What each part of P0118 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 1 | Area: fuel and air metering. |
| 18 | The exact fault in that area. |
What to do next
- Note P0118 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0118
What does P0118 mean?
P0118 means "Engine Coolant Temperature Sensor 1 Circuit High". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0118?
Drive gently and only to a workshop. With P0118 the car can go into limp mode (reduced power) to protect itself.
Will P0118 fail an emissions test?
Yes, it can. P0118 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0118 to fix?
Difficulty: easy. A typical repair takes 0.3 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0118 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.