P0939
Hydraulic Oil Temperature Sensor Circuit Low
- Severity
- Medium
- Driving
- Drivable — book it in
The hydraulic oil temperature signal is stuck low, which reads as implausibly hot on a typical sensor whose resistance falls as temperature rises. Electrically this is usually shorted to earth. The module treats the reading as unusable and drives the actuators conservatively, so gear changes may feel slow or harsh.
Possible causes
- CommonWiring shorted to earth between the sensor and the module
- CommonFailed temperature sensor
- CommonCorroded or fluid-contaminated connector
- PossibleLoss of the sensor earth
- RareGenuinely extreme fluid temperature - rare, but check before assuming a sensor fault
What you might notice
- Slow or harsh gear changes
- Temperature reading implausible
- Transmission warning message
- Check engine light on
What to check, in order
- Read the temperature on a cold vehicle. A reading nowhere near ambient confirms the circuit rather than a genuine temperature.
- Unplug the sensor and check whether the low reading persists at the harness.
- Check the sensor earth before assuming a shorted signal wire.
- Inspect the connector for corrosion and fluid.
- Check the fluid level and condition.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Transmission and control modules
P0900P0901P0902P0903P0904P0905P0906P0907P0908P0909P0910P0911P0912P0913P0914P0915P0916P0917P0918P0919P0920P0921P0922P0923P0924P0925P0926P0927P0928P0929P0930P0931P0932P0933P0934P0935P0936P0937P0938P0939P0940P0941P0942P0943P0944P0945P0946P0947P0948P0949P0950P0951P0952P0953P0954P0955P0956P0957P0958P0959P0960P0961P0962P0963P0964P0965P0966P0967P0968P0969P0970P0971P0972P0973P0974P0975P0976P0977P0978P0979P0980P0981P0982P0983P0984P0985P0986P0987P0988P0989P0990P0991P0992P0993P0994P0995P0996P0997P0998P0999