Engine Coolant Temperature High

The engine's computer is detecting that the coolant temperature is higher than the normal operating range, usually over 220°F (104°C).

The engine control module (ECM) monitors the coolant temperature through the engine coolant temperature sensor. It expects a voltage corresponding to a temperature between 170°F (77°C) and 220°F (104°C). If it sees a consistent reading above this range, it triggers the fault code.

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 and radiator. If low, fill to proper level and recheck. Decision: If coolant was low, monitor for leaks; if coolant level is okay, proceed to step 2.
2. 22. Inspect the wiring and connector at the coolant temperature sensor for corrosion or damage. Repair any issues found. Decision: If wiring is good, proceed to step 3; if there are issues, repair and recheck codes.
3. 33. Test the coolant temperature sensor with a multimeter. At 200°F (93°C), you should see around a 0.5V signal. If the voltage is out of this range, replace the sensor. Decision: If sensor tests bad, replace it; if within range, proceed to step 4.
4. 44. Check the thermostat operation - remove it and place it in hot water. It should open at around 195°F (91°C). If it doesn't open, replace it. Decision: If thermostat is faulty, replace and recheck; if it’s operating correctly, proceed to step 5.
5. 55. Inspect the radiator for blockages and ensure the cooling fans are operational. The fans should engage when the coolant reaches around 220°F (104°C). Decision: If fans aren’t working or there’s blockage, repair as needed. If everything appears normal, further diagnostic testing may be required.

• Low coolant level
• Faulty coolant temperature sensor
• Thermostat stuck closed
• Cooling system blockage or air pockets
• Radiator fan failure

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