FMI 5 - Engine Coolant Temperature Sensor Voltage Above Normal
Engine coolant temperature signal is too high.
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What it means (plain English)
The engine control module is seeing a higher than expected voltage from the coolant temperature sensor, which suggests the sensor is reading too hot or there's a wiring issue delivering incorrect voltage.
What the computer is actually seeing
The ECM sees a voltage above 4.5 volts from the coolant temperature sensor, when it should typically be between 0.5 to 4.5 volts based on engine temperature.
What a healthy reading looks like
Coolant temperature sensor voltage should be between 0.5 to 4.5 volts, depending on engine temperature: e.g., at 200°F (93°C), it should be around 2-2.5 volts.
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 at the coolant temperature sensor for damage or corrosion. If damaged, repair or replace the harness/connectors. Decision: If no damage, proceed to step 2.
- 22. Measure the voltage at the coolant temperature sensor with the engine running. It should be between 0.5 to 4.5 volts. Decision: If it's over 4.5 volts, go to step 3; if normal, replace the sensor because it might be reading incorrectly.
- 33. Disconnect the coolant temperature sensor and measure the resistance to ground. If you find resistance close to 0 ohms, you have a short somewhere; repair as necessary. If resistance is okay, replace the sensor.
Common causes
- Faulty engine coolant temperature sensor
- Wiring issues (short or bad ground)
- Corroded connectors
- ECM issue
- Coolant leak affecting sensor operation
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's safe to drive but monitor engine temperature closely to avoid overheating.
Will this code return after I clear it?
If the underlying issue is not fixed, it will likely come back after clearing and driving.
Why does this code pair with others?
This code can trigger alongside others due to the whole engine management system reading temperatures and coolant levels.
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