Engine Temperature Sensor Circuit Low Voltage
The engine temperature sensor circuit is reading lower than expected voltage.
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What it means (plain English)
The computer expects a certain voltage signal from the engine temperature sensor, but it's seeing a voltage that is too low, which can mean the sensor is faulty or there's a wiring issue.
What the computer is actually seeing
The Engine Control Module (ECM) is looking for the engine temperature sensor to output a voltage between 0.5V and 4.5V. When the reading drops below 0.5V, it triggers SPN 179.
What a healthy reading looks like
Engine temperature should produce between 0.5V (cold) to 4.5V (hot) depending on the engine's temperature.
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. Inspect wiring and connectors related to the engine temperature sensor for damage or corrosion. Fix if necessary. Decision: If wiring is okay, go to step 2.
- 22. Check the engine temperature sensor resistance using a multimeter. At room temperature, expect around 3,000 to 5,000 ohms. Decision: If out of range, replace the sensor. If okay, proceed to step 3.
- 33. Using a scan tool, monitor the engine temperature sensor voltage while the engine is running. Should be between 0.5V and 4.5V. Decision: If voltage is below 0.5V, check for a short. If okay, consider replacing the ECM.
Common causes
- Faulty engine temperature sensor
- Damaged wiring or connectors
- Short circuit in sensor circuit
- Corrosion at the connector
Typical repair cost
$$
Related codes
Frequently asked questions
Can I drive with this code active?
Yes, but monitor engine behavior and temperature closely, as driving with incorrect readings can lead to overheating.
Will this code come back?
If the underlying issue isn't fixed (like wiring or a bad sensor), yes, it will likely return.
Why does this code sometimes appear with other codes?
Multiple codes can indicate a systemic issue, such as a common wiring fault affecting multiple sensors.
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