Engine Coolant Temperature Sensor Circuit Malfunction

The engine coolant temperature sensor measures how hot the coolant is. If it gives a bad reading or is shorted, the computer can't accurately control engine performance and emissions.

The engine control module (ECM) expects a voltage signal from the coolant temperature sensor that changes with temperature. Normally, a cold engine should see about 5 volts (V), and as it heats up, the voltage should drop towards 0.5 V. If this signal is outside the expected range, the code is triggered.

Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.

1. 11. Check the engine coolant level. Should be within normal range (usually marked on the reservoir). If low, refill and retest.
2. 22. Inspect the wiring harness and connector for damage, corrosion, or loose connections. Repair as necessary.
3. 33. Use a multimeter to measure the resistance of the coolant temperature sensor. At room temperature (68°F or 20°C), it should be approximately 2.2k ohms. If out of range, replace the sensor.
4. 44. Start the engine and monitor the coolant temperature sensor voltage with a scan tool. Ensure the readings are between 0.5 V (hot) to 4.5 V (cold). If out of range upon warming, replace the sensor.

• Faulty engine coolant temperature sensor
• Wiring issues (shorts or opens)
• Poor connector contact
• Faulty ECM
• Coolant level low affecting sensor positioning

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