Coolant Temperature Out of Range - High
The coolant temperature is higher than expected during operation.
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What it means (plain English)
The computer thinks the engine’s coolant is way too hot—above 240°F (115°C)—which can mean it's overheating or a sensor issue.
What the computer is actually seeing
The ECM sees coolant temperature sensor readings above 240°F (115°C). This reading is higher than the specified operational range for the engine, which typically runs around 190°F to 220°F (88°C to 104°C).
What a healthy reading looks like
Coolant temperatures should be between 190°F and 220°F (88°C to 104°C) under normal operating conditions.
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—ensure it's at the proper level. If it's low, top it off and check for leaks.
- 2Inspect the coolant temperature sensor connector for damage or corrosion—repair or clean as necessary.
- 3Use a scan tool to read current coolant temperature. If above 240°F (115°C), proceed to the next step; if not, recheck sensor and wiring.
- 4Test the coolant temperature sensor using a multimeter. At ambient temperature (about 70°F or 21°C), you should see approximately 2.5kΩ resistance. If it's off significantly, replace the sensor.
- 5Check for thermostat operation—remove the thermostat and test it in hot water. It should begin to open around 195°F (90°C). If it doesn't, replace it.
Common causes
- Faulty coolant temperature sensor
- Coolant leaks causing insufficient coolant levels
- Faulty thermostat stuck closed
- Wiring issues or bad connections to the coolant temperature sensor
- Overheating engine due to low coolant or cooling system failure
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code active?
It's not recommended; overheating can damage your engine.
Will the code come back after I clear it?
If the issue is not resolved—like a bad sensor or thermostat—it will return.
Why does this code show up with SPN 1684?
Both codes relate to coolant temperature issues; a fault in one can affect readings in the other.
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