Coolant Temperature Sensor 1
The engine's coolant temperature sensor is reading out of range.
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What it means (plain English)
The coolant temperature sensor measures how hot the engine coolant is. If it reads too high or too low, the engine computer thinks there's a problem with the engine's temperature.
What the computer is actually seeing
The engine control module (ECM) sees the current coolant temperature readings from the sensor. Normally, these should range from about 180°F (82°C) to 220°F (104°C) when the engine is running. If the reading goes below 140°F (60°C) or above 250°F (121°C), it triggers SPN 5595.
What a healthy reading looks like
180°F to 220°F (82°C to 104°C) during normal operation; should not fall below 140°F or exceed 250°F.
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 the coolant level in the reservoir. Ensure it's at the proper level. If low, refill and retest. Decision: If the level was low and the issue is resolved, monitor for recurrence.
- 22. Inspect the wiring and connector for the coolant temperature sensor for damage or corrosion. Ensure the connection is secure. Decision: If damaged, repair/replace wiring and retest.
- 33. Use a scan tool to check the current coolant temperature reading. Compare it with a trusted thermometer reading from the engine's coolant. Decision: If the readings are inconsistent, suspect a faulty sensor.
- 44. If the sensor appears to be functioning correctly, check the engine coolant thermostat to make sure it's opening and closing properly. Decision: If stuck open or closed, replace the thermostat.
Common causes
- Faulty coolant temperature sensor
- Wiring or connector issues to the sensor
- Low coolant level or air in the system
- Faulty engine coolant thermostat
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code active?
It's generally safe to drive but monitor engine temperature closely. If the engine begins to overheat, pull over and stop driving immediately.
Will this code come back after clearing it?
It may come back if the underlying issue, like a faulty sensor or bad wiring, isn't addressed.
Can this code be related to other problems?
Yes, it can also pair with codes related to overheating, thermostat issues, or even engine performance problems.
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