FMI 3 - Transmission Fluid Temperature Sensor Circuit High
The transmission fluid temperature sensor is sending a high voltage signal.
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What it means (plain English)
The transmission fluid temperature sensor is telling the engine computer that the fluid is hotter than it should be, indicating a possible overheating issue or sensor failure.
What the computer is actually seeing
The engine control module (ECM) sees a voltage from the temperature sensor that exceeds the manufacturer-defined threshold, often above 4.0 volts when the expected range is around 0.5 to 2.5 volts.
What a healthy reading looks like
Typical operational voltage from the transmission fluid temperature sensor should be between 0.5V and 2.5V, with overheating conditions rising above 4.0V.
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 transmission fluid level; it should be within manufacturer specs. If low, top off and recheck the code after driving.
- 22. Inspect wiring and connectors at the transmission fluid temperature sensor for corrosion, damage, or loose connections.
- 33. Use a digital multimeter to measure the voltage output of the transmission fluid temperature sensor while the engine is running. Check for values between 0.5V to 2.5V.
- 44. If voltage is above 4.0V, replace the transmission fluid temperature sensor and clear the code before retesting.
- 55. If normal voltage is still present after replacing the sensor, inspect the wiring for shorts or opens using the wiring diagram.
Common causes
- Faulty transmission fluid temperature sensor
- Short circuit in the wiring harness
- Open circuit in the wiring harness
- Low transmission fluid level
- Overheating transmission
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with SPN 0786 active?
It's not recommended to drive long distances as it indicates possible overheating which can damage the transmission.
Will the code come back after replacing the sensor?
If the actual overheating issue is resolved and the wiring is intact, the code should not return.
Why does this code sometimes pair with SPN 0785?
SPN 0785 indicates a similar issue with the transmission fluid temperature sensor circuit. They may be triggered together if there is a common fault in the wiring or sensor.
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