To return temperature data to the ECU, the hydraulic oil temperature sensor uses an electrical signal that returns to the engine computer through a series of wires and connectors. If an abnormally low voltage signal is detected on the hydraulic oil temperature sensor circuit, a DTC P0939 will be recorded.
How severe is the code?
Diagnostic trouble code P0939 is very serious, as it means the ECU may not be able to prevent overheating and severe internal damage without reliable hydraulic oil temperature data.
Symptoms
Symptoms of a P0939 include:
- Check engine light
- Overheating
- Erratic vehicle behavior
- Limp mode
Causes
- Corroded/broken connectors
- Damaged wiring
- Faulty hydraulic oil temperature sensor
- Hydraulic fluid level too low
- Dirty hydraulic fluid
How to diagnose the code?
The diagnostic process for OBDII trouble code P0939 should begin with checking the level and condition of the hydraulic oil itself (if dirty, change it). The wiring and connectors along the circuit should also be carefully inspected for signs of damage on wires and corroded or broken connectors. If no issues are detected, the hydraulic oil temperature sensor will need to be tested. The ECU itself may also need to be reprogrammed or replaced.
What repairs will fix P0939?
- Repair damaged wiring and/or connectors
- Replace the hydraulic oil temperature sensor
- Change the hydraulic fluid
- Reprogram or replace the ECU