Engine Cooler Thermostat Control Performance
The cooling system thermostat is not functioning as required.
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What it means (plain English)
The thermostat controls the engine temperature by regulating coolant flow. If it's stuck open or closed, your engine won't heat up or cool down properly, affecting performance and emissions.
What the computer is actually seeing
The engine control module (ECM) expects the coolant temperature to rise to a specified level (typically around 185-205°F) within a certain time (usually 2-3 minutes after startup). If the temperature change is too slow or remains outside expectations, the code triggers.
What a healthy reading looks like
Coolant temperature should reach at least 185°F within 4 minutes of engine startup; it should not exceed 220°F under normal operation.
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; it should be at the proper level, not low. If low, refill and recheck for leaks.
- 2Inspect wiring and connectors to the thermostat for damage or corrosion. Repair or replace if necessary.
- 3Test the thermostat by monitoring coolant temperature during engine warm-up; it should begin opening around 185°F.
- 4If the thermostat is stuck open (engine never reaches operating temperature), replace the thermostat and recheck.
- 5If no issue found with coolant level, wiring, or thermostat, check the coolant temperature sensor for proper operation.
Common causes
- Faulty thermostat
- Wiring issues to the thermostat
- Coolant leakage
- Incorrect coolant level
- Temperature sensor malfunction
Typical repair cost
$$-$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's advisable to fix this soon, as prolonged driving can lead to engine performance issues and increased emissions.
Will this code come back after clearing it?
If the underlying issue isn't resolved, it's likely the code will return.
Why does this code pair with SPN 1339?
SPN 1339 often indicates a similar problem with the engine coolant temperature sensor, which can affect thermostat performance.
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