Engine Coolant Temperature Above Normal Operational Range
The engine coolant temperature is too high for normal operation.
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What it means (plain English)
The coolant temperature sensor (CTS) is detecting that the engine is overheating, typically above 220°F (104°C).
What the computer is actually seeing
The engine control module (ECM) monitors the coolant temperature sensor for a voltage reading. A proper signal shows a range of 0.5V (at -40°F) to 4.5V (at 257°F). When the signal exceeds an expected range indicating a temperature above normal, it triggers SPN 338.
What a healthy reading looks like
Coolant temperature should ideally be between 180°F and 220°F (82°C to 104°C).
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 coolant level in the reservoir and radiator; top off if low and look for leaks.
- 22. Inspect the coolant temperature sensor connector for corrosion or looseness; repair as necessary.
- 33. Using a scan tool, compare actual coolant temperature with the reading from the ECM; they should match closely.
- 44. If the coolant temp sensor reads inaccurately, replace the coolant temperature sensor and retest.
- 55. If levels are normal but overheating continues, inspect the thermostat by removing it and checking it in hot water; it should fully open at the specified temperature.
- 66. If still no success, check the water pump for proper operation and look for blockages in the cooling system.
Common causes
- Coolant level low or coolant leak
- Faulty thermostat stuck closed
- Faulty coolant temperature sensor
- Cooling system blockages
- Faulty water pump
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code active?
No, continue driving can cause severe engine damage due to overheating.
If I clear the code, will it come back?
Yes, if the underlying issue isn't fixed, the code will likely return after the engine reaches operating temperature.
Why does this code sometimes pair with SPN 130?
SPN 130 relates to the engine oil temperature that can also rise if the engine is overheating.
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