Engine Coolant Temperature Sensor Circuit Low
The engine coolant temperature sensor signal is too low.
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What it means (plain English)
The engine thinks the coolant is way too cold, which can cause it to run poorly and waste fuel.
What the computer is actually seeing
The engine control module (ECM) sees the coolant temperature sensor sending a signal below a threshold, usually around 0.2 volts or less when it should be between 0.5 to 4.5 volts during operation.
What a healthy reading looks like
Coolant temperature signal should range from 0.5V (cold) to 4.5V (hot), corresponding to temperatures from about -40°F to 248°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.
- 1Check coolant level in the reservoir; ensure it's at the proper level.
- 2Inspect wiring and connectors for signs of damage or corrosion.
- 3Measure voltage at the coolant temperature sensor connector. It should show between 0.5V and 4.5V based on coolant temperature.
- 4If voltage is below 0.5V, replace the coolant temperature sensor and retest.
- 5If voltage is normal, check for any stored codes that might indicate further issues with the ECM.
Common causes
- Faulty coolant temperature sensor
- Wiring issues or bad connectors
- Coolant level low or air trapped in the system
- ECM malfunction
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
Moderately safe if the engine isn't overheating, but fuel efficiency will be impacted.
Will this code come back after I clear it?
Yes, if the root cause isn't fixed; replacing the sensor without checking the wiring could lead to a return.
Why does this code pair with others like SPN 100 ?
Other SPNs may indicate related issues, often tied to engine cooling and temperature regulation, so it's common to see them together.
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