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SensorsSeverity Medium: diagnose soon

P0115Engine Coolant Temperature Sensor 1 Circuit

What it means

The ECU has detected an electrical fault in the engine coolant temperature sensor circuit. 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

  • Open or shorted wiring between the sensor and the ECU
  • Corroded or loose connector
  • Failed engine coolant temperature sensor

What to check first

  1. Compare the live reading with the real temperature (IR thermometer)
  2. Measure the sensor resistance and compare it with the temperature table
  3. Check the 5 V pull-up and the ground at the connector
Can I drive with P0115? 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 P0115

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

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P0115: questions and answers

What does P0115 mean?

P0115: Engine Coolant Temperature Sensor 1 Circuit. The ECU has detected an electrical fault in the engine coolant temperature sensor circuit. The ECU uses coolant temperature for cold-start fuelling, idle speed, the radiator fan and the temperature gauge.

What are the symptoms of P0115?

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

What causes P0115?

Open or shorted wiring between the sensor and the ECU. Corroded or loose connector. Failed engine coolant temperature sensor.

How do you diagnose P0115?

1. Compare the live reading with the real temperature (IR thermometer) 2. Measure the sensor resistance and compare it with the temperature table 3. Check the 5 V pull-up and the ground at the connector

Can I drive with P0115?

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