What it means
The hydraulic oil temperature sensor reports a range/performance 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 sends fluid temperature feedback to the TCM for transmission control. P0938 sets when the reading is implausible or changes outside the expected range or response pattern, even if the circuit is not simply stuck high or low.
Common causes
Most likely first.
- Temperature sensor failed
- Wiring fault
- Sensor element aged beyond calibration window
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 temperature data with ambient temperature when cold, then observe whether it rises plausibly as the transmission warms.
- Inspect the temperature sensor and harness for damage, poor connections, corrosion, or routing that could expose wiring to heat or vibration.
- Check the sensor signal, reference or supply, and ground circuits against the manufacturer's wiring information for unstable or out-of-range behavior.
- If the circuit checks out, test whether the sensor responds smoothly to changing fluid temperature using the manufacturer's procedure.
- Replace only the confirmed faulty sensor or repair the circuit, then verify that the temperature reading tracks warm-up normally.
Common fixes
- Clean and secure a loose or corroded temperature sensor connection.
- Repair damaged or unstable wiring in the sensor circuit.
- Replace the hydraulic oil temperature sensor if its response is outside the manufacturer's expected range.
- Recheck temperature feedback after repair to confirm it changes plausibly with warm-up.
Can I keep driving?
If the transmission shifts normally, keep driving limited and avoid heavy loads until the temperature reading is reliable. Stop if shifting becomes harsh, the transmission slips, or a warning indicates 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.