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P0118Engine Coolant Temperature Sensor 1 Circuit High

What it means

The engine coolant temperature sensor signal voltage is too high. For this type of sensor that means the ECU sees an impossibly low temperature (about −40 °C), usually because the circuit is open. The ECU uses coolant temperature for cold-start fuelling, idle speed, the radiator fan and the temperature gauge.

Symptoms

  • Fan runs all the time (failsafe)
  • High fuel consumption and rich running
  • Hard hot starts, high idle

Common causes

  • Open signal or ground wire
  • Unplugged or corroded connector
  • Open circuit inside the sensor

What to check first

  1. Live data shows about −40 °C
  2. Bridge the connector terminals with a jumper: the reading should jump to a very high value
  3. Measure the sensor resistance (OL means it is open)
Can I drive with P0118? Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.
Practise it: Coolant temperature sensor in the engine simulator shows this fault in live data, tests and on the scope.Open in the simulator

Generic OBD-II meaning. Manufacturer-specific meanings and checks can differ; always check the service information for the car.

How to test the parts behind P0118

Coolant temperature sensor (ECT)Wiring, typical values, multimeter and scope tests

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P0118: questions and answers

What does P0118 mean?

P0118: Engine Coolant Temperature Sensor 1 Circuit High. The engine coolant temperature sensor signal voltage is too high. For this type of sensor that means the ECU sees an impossibly low temperature (about −40 °C), usually because the circuit is open. The ECU uses coolant temperature for cold-start fuelling, idle speed, the radiator fan and the temperature gauge.

What are the symptoms of P0118?

Fan runs all the time (failsafe). High fuel consumption and rich running. Hard hot starts, high idle.

What causes P0118?

Open signal or ground wire. Unplugged or corroded connector. Open circuit inside the sensor.

How do you diagnose P0118?

1. Live data shows about −40 °C 2. Bridge the connector terminals with a jumper: the reading should jump to a very high value 3. Measure the sensor resistance (OL means it is open)

Can I drive with P0118?

Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.