Engine Coolant Temperature - Fault
Indicates that the engine coolant temperature is outside the normal range.
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What it means (plain English)
The computer is detecting that the engine coolant temperature is either too high or too low, which can indicate overheating or a cooling system failure.
What the computer is actually seeing
The engine control unit (ECU) monitors the coolant temperature sensor signal, which should fluctuate between 180°F and 220°F (82°C to 104°C) during normal operation. If the signal is below 140°F (60°C) or above 250°F (121°C), a fault code is triggered.
What a healthy reading looks like
Normal coolant temperature should 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: Ensure the engine is cool, then check the radiator and overflow tank for adequate coolant levels. If low, top off and check for leaks.
- 22. Inspect wiring and connectors: Look for damaged, corroded, or loose connections at the coolant temp sensor. Repair as needed.
- 33. Test the coolant temperature sensor: Use a multimeter to check resistance at the sensor. It should show 10,000 ohms at 176°F (80°C). Replace sensor if readings are outside normal range.
- 44. Verify thermostat operation: Check that the thermostat opens at the correct temperature. Replace if it’s stuck closed or open.
- 55. Confirm engine operation: Start the engine and monitor coolant temperature with a scan tool. It should rise steadily to expected values. If overheating occurs, further diagnose the cooling system.
Common causes
- Faulty coolant temperature sensor
- Wiring issues or bad connections
- Low coolant level
- Faulty thermostat
- Cooling system blockage or leaks
Typical repair cost
$$$
Related codes
Frequently asked questions
Can I drive the vehicle with this code active?
Yes, but monitor temperature closely. If it overheats, pull over immediately.
Will this code come back after I clear it?
If the underlying issue isn't resolved, it likely will return.
Why does this code sometimes pair with SPN 510?
SPN 510 indicates a circuit fault in the temperature sensor, which can occur due to the same wiring or sensor issues.
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