Engine Coolant Temperature Too High
The engine's coolant temperature is higher than normal operating range.
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What it means (plain English)
The engine coolant temperature sensor is picking up heat that is above normal. This usually means the engine is overheating, which can cause serious damage if not addressed.
What the computer is actually seeing
The coolant temperature sensor sends a voltage signal to the engine control module (ECM) that varies from 0.5V (cold) to 4.5V (hot). If the voltage indicates a temperature above 230°F (110°C), the code is triggered.
What a healthy reading looks like
Normal operating coolant temperature is between 180°F and 220°F (82°C to 104°C). Above 230°F (110°C) triggers the code.
Guided diagnostic — the DiagCoach way
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.
- 11. Check the coolant level in the reservoir and radiator. If low, top up and reassess.
- 22. Inspect coolant hoses for leaks or cracks that might lead to coolant loss.
- 33. Test the coolant temperature sensor. At 200°F (93°C), the resistance should be around 2.2k ohms. If it’s out of spec, replace it.
- 44. Verify that the thermostat opens at around 195°F (90°C); it may be stuck closed causing overheating.
- 55. Check the operation of the water pump. Look for leaks or a loose belt causing improper water circulation.
- 66. If temperature remains high after these checks, inspect for potential engine damage.
Common causes
- Low coolant level
- Faulty coolant temperature sensor
- Worn water pump
- Radiator blockage
- Thermostat stuck closed
- Engine running excessively rich
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
No, it's high severity; the engine could overheat and cause serious damage.
Will this code come back if I clear it?
If the underlying issue isn't fixed, yes, it will likely return.
Why does this code come up with SPN 100?
SPN 100 is generally about engine speed, and if the engine is overheating, it can affect performance, so they often trigger together.
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