What it means
The hydraulic oil temperature sensor reports a circuit high fault. Oil temperature feedback for hydraulic system is unreliable.
At a glance
- Usually lights the check-engine light
How it works
The hydraulic oil temperature sensor reports fluid temperature to the TCM so it can manage transmission operation. P0940 sets when the sensor circuit signal is higher than expected, potentially because the signal wire is shorted to battery power, the sensor is open, or a connection has excessive resistance.
Common causes
Most likely first.
- Signal wire shorted to B+
- Open sensor
- Connector pins corroded - high contact resistance
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Record freeze-frame data and compare live oil temperature data with ambient conditions when cold to see whether the signal is implausibly high.
- Inspect the temperature sensor connector and wiring for corrosion, loose pins, damage, or a signal wire shorted to battery power.
- Check the signal, reference or supply, and ground circuits against the manufacturer's wiring information, looking for unintended high voltage or an open circuit.
- If the wiring and connector are sound, test the temperature sensor using the manufacturer's procedure.
- Repair the confirmed circuit or sensor fault, then confirm the live temperature reading behaves plausibly as the transmission warms.
Common fixes
- Clean and secure corroded or loose temperature sensor connector pins.
- Repair a signal wire shorted to battery power or otherwise damaged wiring.
- Replace the temperature sensor if it is open or produces a high signal with sound wiring.
- Clear the code and verify plausible temperature feedback after repair.
Can I keep driving?
If shifting is normal, limit driving and avoid heavy loads until the TCM receives reliable oil temperature data. Stop if the transmission slips, shudders, shifts harshly, or enters limp mode.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.