Engine Over Temperature

When the engine temperature exceeds 230°F (110°C), the ECU detects this and triggers a warning. This typically means something is wrong in the cooling system or with the engine itself.

The onboard computer monitors the engine coolant temperature sensor (ECT) signal, which should normally display a voltage between 0.5V (cold) and 4.5V (hot). Once the temperature crosses 230°F (110°C), it sets SPN 994.

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. Is it low? If yes, refill and monitor temperatures again. Decision: If problem persists, continue; if not, vehicle is fixed.
2. 22. Inspect for any visible coolant leaks around hoses and fittings. Are there leaks present? If yes, repair leaks. Decision: If problem persists, continue; if not, vehicle is fixed.
3. 33. Check the operation of the thermostat by removing it and testing in hot water. Does it open at the specified temperature (usually around 195°F / 91°C)? If no, replace thermostat. Decision: If replaced and problem persists, continue; if not, vehicle is fixed.
4. 44. Test the water pump for operation. Is it circulating coolant properly? If no, replace the water pump. Decision: If replaced and problem persists, continue; if not, vehicle is fixed.
5. 55. Inspect the radiator for blockages or damage. Is airflow restricted? If yes, clean or replace as needed. Decision: If replaced/cleaned and problem persists, continue; if not, vehicle is fixed.

• Low coolant levels
• Faulty thermostat
• Malfunctioning water pump
• Blocked radiator
• Coolant leaks

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