Engine Coolant Temperature Too High
Engine coolant temperature is abnormally high, indicating overheating conditions.
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What it means (plain English)
The engine's computer is seeing that the coolant temperature sensor is reading above the normal range, usually over 220°F (104°C). This can occur if the engine is actually overheating or if the sensor is faulty.
What the computer is actually seeing
The ECM is receiving a coolant temperature signal from the sensor (usually a 0.5 to 4.5V signal). If this voltage exceeds 4.5V or drops below 0.5V, the ECM triggers the code.
What a healthy reading looks like
Normal coolant temperature range is 195°F to 220°F (90°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.
- 1Check coolant level in the reservoir and radiator. If low, top off and retest.
- 2Inspect for external leaks around hoses and the radiator. Repair any leaks found.
- 3With the engine running, monitor the coolant temperature using a scan tool. Is it over 220°F (104°C)? If yes, proceed to the next step. If no, it may be a sensor issue.
- 4Check if engine fans are operating when temperatures exceed normal. If fans are not running, test fan relay and fuses.
- 5Remove the thermostat and test its operation by placing it in hot water. Does it open at specified temperature (usually around 195°F/90°C)? If not, replace the thermostat.
Common causes
- Low coolant level
- Thermostat stuck closed
- Cooling fan not operating
- Faulty coolant temperature sensor
- Blocked radiator or coolant passages
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It’s not safe to drive if the engine is actually overheating; this can cause severe engine damage.
Will this code come back after I fix it?
If the root cause is corrected, the code should not return. However, a faulty sensor may recreate the issue.
Why does this code pair with SPN 310?
SPN 310 relates to the cooling fan and could indicate that the fan isn't functioning, causing the engine to overheat.
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