Engine Coolant Temperature Sensor Circuit High

The engine's computer thinks the coolant is way too hot, which could mean the engine is actually overheating or the sensor is malfunctioning.

The Engine Control Module (ECM) is getting a voltage signal from the coolant temperature sensor that exceeds its normal range, usually above 5 volts or below 0.5 volts, where it expects to see between 0.5V and 4.5V.

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 coolant level in the reservoir; it should be between the min and max marks. If it's low, top it off and see if the code returns. Decision point: If the coolant was low and the code returns, continue diagnostics. If not, the issue may be resolved.
2. 22. Inspect the wiring and connectors for the coolant temperature sensor for any damage, disconnection, or corrosion. Decision point: If wiring damage is found, repair it and retest. If wiring is intact, proceed to step 3.
3. 33. Test the voltage at the coolant temperature sensor connector. At a normal operating temperature of around 200°F, you should see about 2.5V. Decision point: If the voltage is too high (above 4.5V) or too low (below 0.5V), replace the sensor. If the voltage is correct, check the ECM next.
4. 44. If the sensor tests okay, check the ECM for faults or damage, including any other fault codes present. Decision point: If the ECM is failing or showing faults, replace it; if not, further diagnostics may be needed.

• Failed engine coolant temperature sensor
• Wiring issues or short circuits
• Faulty Engine Control Module (ECM)
• Coolant overheating due to low levels or a malfunctioning thermostat

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