P0118 moderate

Engine Coolant Temperature Sensor 1 Circuit High Input

What does P0118 mean?

The P0118 code means the vehicle's onboard diagnostic system has detected: Engine Coolant Temperature Sensor 1 Circuit High Input. This is a moderate severity code.

Common Symptoms

  • Check Engine Light on
  • Engine runs rich on warm restarts
  • Temperature gauge reads cold or not at all
  • Heater may not work properly
  • Hard warm starting

Probable Causes (Ranked by Likelihood)

  • ECT sensor open circuit reading maximum resistance Very High
  • Open signal wire between sensor and PCM High
  • Disconnected sensor connector Moderate
  • Corroded or broken sensor terminal Moderate

Step-by-Step Diagnostic Procedure

  1. Check ECT signal voltage: above 4.7V at operating temperature indicates an open circuit.

  2. Disconnect and reconnect the ECT connector. If the fault clears, the connector was loose.

  3. Measure sensor resistance at operating temperature. Should be 200-300 ohms when hot. Infinite resistance indicates open sensor.

  4. Check wiring continuity.

  5. Replace sensor if open internally.

Frequently Asked Questions

My temperature gauge reads stone cold even though the engine is warm -- is this P0118?

Possibly. A high ECT input (open circuit) causes the ECU to assume maximum cold temperature, which may drive the gauge to cold. It may also cause a rich running condition on startup since the ECU thinks it is always cold.

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