Engine Coolant Temperature Sensor Low
The engine coolant temperature sensor is reporting a low voltage signal.
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What it means (plain English)
When the engine coolant temperature sensor sends a low voltage reading, it indicates that the sensor is detecting that the coolant temperature is too low, which could lead the engine to run inefficiently or not reach operating temperature.
What the computer is actually seeing
The Engine Control Module (ECM) sees a voltage below 0.1 volts from the coolant temperature sensor when it should be around 0.5 to 4.5 volts.
What a healthy reading looks like
Normal operating voltage from the coolant temperature sensor should range from 0.5V (cold) to 4.5V (hot).
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 engine coolant level. Ensure it is within the recommended range. If low, fill to the proper level and retest.
- 22. Inspect the wiring and connectors for damage or corrosion between the coolant temperature sensor and the ECM. Repair as necessary and retest.
- 33. Measure the voltage at the coolant temperature sensor connector with the engine on. Expected value is between 0.5V to 4.5V.
- 44. If the voltage is below 0.1V, replace the coolant temperature sensor. If it reads normal, further diagnose the ECM.
Common causes
- Faulty engine coolant temperature sensor
- Poor electrical connection or damaged wiring
- Coolant level too low or incorrect coolant
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
While it's drivable, it may cause engine performance issues, leading to poor fuel economy and possible overheating.
Will this code come back?
If root causes like sensor failure or wiring issues are not fixed, the code will likely return.
Why does this code pair with SPN 425?
SPN 425 indicates high coolant temperature; a mismatch in readings can trigger both codes if there’s a sensor issue.
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