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SensorsSeverity Medium: diagnose soon

P0117Engine Coolant Temperature Sensor 1 Circuit Low

What it means

The engine coolant temperature sensor signal voltage is too low. For this type of sensor that means the ECU sees an impossibly high temperature, usually because the signal wire is shorted to ground. The ECU uses coolant temperature for cold-start fuelling, idle speed, the radiator fan and the temperature gauge.

Symptoms

  • Hard starting, rich running or black smoke
  • Radiator fan running all the time
  • High idle or wrong temperature gauge

Common causes

  • Signal wire shorted to ground
  • Sensor shorted internally
  • Water in the connector

What to check first

  1. Live data usually shows a very high temperature (130 °C or more) with a cold engine
  2. Unplug the sensor: the reading should drop to about −40 °C
  3. Check the harness for chafing to ground
Can I drive with P0117? Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.

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 P0117

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

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P0117: questions and answers

What does P0117 mean?

P0117: Engine Coolant Temperature Sensor 1 Circuit Low. The engine coolant temperature sensor signal voltage is too low. For this type of sensor that means the ECU sees an impossibly high temperature, usually because the signal wire is shorted to ground. The ECU uses coolant temperature for cold-start fuelling, idle speed, the radiator fan and the temperature gauge.

What are the symptoms of P0117?

Hard starting, rich running or black smoke. Radiator fan running all the time. High idle or wrong temperature gauge.

What causes P0117?

Signal wire shorted to ground. Sensor shorted internally. Water in the connector.

How do you diagnose P0117?

1. Live data usually shows a very high temperature (130 °C or more) with a cold engine 2. Unplug the sensor: the reading should drop to about −40 °C 3. Check the harness for chafing to ground

Can I drive with P0117?

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