FMI 3 - High Engine Coolant Temperature
The engine control unit has detected an engine coolant temperature that's too high.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The engine's computer sees that the coolant temperature is above normal operating range, typically over 220°F (104°C).
What the computer is actually seeing
The engine control unit (ECU) monitors signals from the coolant temperature sensor. If the temperature reading exceeds the safe threshold (usually over 220°F), it triggers SPN 330.
What a healthy reading looks like
Engine coolant temperature should be between 195°F and 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. Ensure it's at proper level and not low.
- 2Inspect coolant temperature sensor wiring for damage or corrosion. Repair if necessary.
- 3Test the coolant temperature sensor using a multimeter. Check if it reads between 0.5V to 4.5V at various temperature points.
- 4When the engine is running, feel the upper radiator hose. It should be hot; if not, suspect a stuck thermostat.
- 5Ensure the radiator and cooling system are free of blockages or leaks.
Common causes
- Low coolant level
- Faulty coolant temperature sensor
- Thermostat is stuck closed
- Coolant leaks
- Blocked radiator or hoses
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
Not usually, you risk overheating the engine if coolant temperatures are too high.
Will the code come back after I fix it?
If the underlying issue is resolved, the code should clear; but if not addressed, it may return.
Why does this code often pair with SPN 331?
SPN 331 represents coolant temperature that's reading too low, which can happen if the sensor is faulty or if there are issues with the cooling system.
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