Hydraulic Oil Temperature Sensor Circuit High Input
The engine computer detected the hydraulic oil temperature sensor is reading too high, similar to a thermometer stuck showing boiling water when the liquid is actually cool. This usually means a wiring problem or a failed sensor sending false high-temperature signals to the transmission control unit.
The ECU monitors voltage output from the hydraulic oil temperature sensor, which should vary between 0.5V and 4.5V depending on actual fluid temperature. When the sensor circuit reads above the maximum threshold voltage continuously, the ECU interprets this as an implausibly high temperature and sets P0940.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Sensor Voltage | 0.5V to 4.5V | >4.5V or open circuit |
| Oil Temperature | -40°C to 150°C | >150°C equivalent signal |
Code P0940 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0940 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.