Coolant Temperature Sensor Voltage Low
The coolant temperature sensor is reporting a low voltage.
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What it means (plain English)
The computer thinks the engine's coolant is too cold because the sensor is sending a low voltage signal, typically below 0.1 volts.
What the computer is actually seeing
The engine control module (ECM) expects the coolant temperature sensor to send a voltage signal that correlates with engine temperature; low voltage indicates a problem with the sensor or circuit.
What a healthy reading looks like
Coolant temperature should show a voltage between 0.5V to 4.5V when the engine is running under normal conditions, correlating to temperatures from approximately 32°F to 240°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 wiring and connectors to the coolant temperature sensor for damage or corrosion. If any issues are found, repair them and retest.
- 22. With the engine at operating temperature, use a multimeter to measure the voltage at the coolant temperature sensor. Confirm if the voltage output is below 0.5V. If it is, continue to step 3.
- 33. Test the resistance of the coolant temperature sensor at ambient temperature; it should typically be between 2,200 ohms (32°F) to about 270 ohms (200°F). If the resistance is out of spec, the sensor is bad.
- 44. If the sensor checks out but the voltage is still low, inspect the wiring harness for shorts to ground or broken wires. Repair any issues found.
- 55. If wiring and the sensor are confirmed functional, suspect ECM malfunction.
Common causes
- Faulty coolant temperature sensor
- Wiring issues (shorts or opens)
- Bad ECM connection or malfunction
- Corroded connectors
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's moderate severity; the engine may run poorly and could lead to overheating if not addressed, so fix it soon.
Will this code come back after repairs?
If you fix the underlying issue (sensor or wiring), it shouldn't come back.
Why does this code sometimes pair with SPN 0128?
SPN 0128 indicates the coolant temperature is too high; if one sensor fails, it can trigger multiple related codes.
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