P0117 moderate

Engine Coolant Temperature Sensor 1 Circuit Low Input

What does P0117 mean?

The P0117 code means the vehicle's onboard diagnostic system has detected: Engine Coolant Temperature Sensor 1 Circuit Low Input. This is a moderate severity code.

Common Symptoms

  • Check Engine Light on
  • Engine runs rich
  • Possible black smoke
  • Poor fuel economy
  • Cooling fan may run continuously

Probable Causes (Ranked by Likelihood)

  • ECT sensor shorted to ground internally Very High
  • Short to ground in ECT signal wiring High
  • Corroded sensor connector bridging signal and ground Moderate

Step-by-Step Diagnostic Procedure

  1. Check ECT voltage: below 0.3V at any temperature indicates a short to ground.

  2. Disconnect the sensor. If voltage rises to 5V at the PCM side, the sensor is faulty.

  3. Inspect wiring for chafing or contact with the engine block.

  4. Clean the connector and retest before replacing the sensor.

Frequently Asked Questions

A low ECT input makes the ECU think the engine is very hot -- what happens?

The ECU cuts the cold-start enrichment and may run a lean mixture. Interestingly, a shorted ECT often also keeps the radiator fan running at all times since the ECU thinks it is overheating.

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