P0939 code meaning
Hydraulic Oil Temperature Sensor Circuit Low
Powertrain system Generic code P09xx codes Check engine light
What P0939 means
The hydraulic oil temperature sensor signal sits below its valid window. With the usual NTC thermistor, a low voltage corresponds to an implausibly hot reading and typically comes from a signal wire shorted to ground or a sensor shorted internally. Ferrari uses P0939 on its DCT for the radiator outlet and gearbox inlet oil temperature sensor, described as signal too low and read in the NCR gearbox ECU. CARB requires out-of-range checks on transmission sensors. P0940 is the high counterpart, P0937 the general circuit fault, P0938 plausibility and P0941 intermittent. Because the module believes the oil is very hot, it may reduce torque, change shift strategy or show an overheat warning.
P0939 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0939
- Gearbox warning or overheat message
- Reduced performance or altered shift behaviour
Common causes of P0939
- Most likelySensor signal wire shorted to ground
- PossibleTemperature sensor shorted internally
- Less likelyControl module input fault
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hydraulic oil temp sensorWiring harnessTCM
What each part of P0939 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 9 | Area: transmission. |
| 39 | The exact fault in that area. |
What to do next
- Note P0939 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0939
What does P0939 mean?
P0939 means "Hydraulic Oil Temperature Sensor Circuit Low". The hydraulic oil temperature sensor signal sits below its valid window. It is a generic code, so it means the same on every make.
Is it safe to drive with P0939?
Drive gently and only to a workshop. With P0939 the car can go into limp mode (reduced power) to protect itself.
Will P0939 fail an emissions test?
Yes, it can. P0939 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0939 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. This is a job for a workshop.
Will P0939 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.