Engine High Temperature Alarm

The engine is running too hot, usually above 230°F (110°C), which can cause serious damage if not addressed quickly.

The engine control module (ECM) sees a coolant temperature reading that exceeds the predefined threshold. This can happen if the temperature sensor shows readings above 230°F (110°C) for more than a set period of time, typically around 5 seconds.

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 coolant level in the reservoir and replace if low. Decision: If low, fill and retest the engine temperature; if not low, proceed to step 2.
2. 22. Inspect for coolant leaks around hoses, radiator, and engine block. Decision: If leaks are found, repair and retest; if no leaks, proceed to step 3.
3. 33. Test the thermostat operation by feeling the upper radiator hose temperature (should be warm) within a few minutes of engine running. Decision: If cold while the engine is hot, replace the thermostat; if hot, proceed to step 4.
4. 44. Check operation of the cooling fans; they should activate when temperature exceeds 220°F (104°C). Decision: If fans do not run, troubleshoot fan relay and power supply; if they run, proceed to step 5.
5. 55. Measure the coolant temperature sensor's resistance with a multimeter. Expected resistance at 200°F (93°C) should be around 1.5 - 2.5 kΩ. Decision: If out of spec, replace the sensor; if within spec, consider further diagnostics on the ECM.

• Low coolant level
• Coolant leaks
• Thermostat malfunction
• Radiator issues
• Faulty coolant temperature sensor

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