Cause
Faulty hydraulic oil temperature sensor
The sensor reporting the temperature of the hydraulic fluid, which the module uses to compensate for how much the fluid's viscosity changes between a cold start and a hot one. The compensation is the point: the same commanded pressure moves an actuator at very different rates through cold thick fluid and hot thin fluid, so a wrong temperature makes every timing calculation wrong with it.
That is why its failure produces complaints that look mechanical. Believing the fluid is colder than it is, the module over-compensates and shifts become harsh once hot; believing it warmer, the mechanism is under-driven and shifts are slow and slurred when cold. Neither symptom points at a temperature sensor, and both are commonly diagnosed as actuator or clutch wear.
It also gates protective strategies, which is the more serious half. A system that cannot trust its fluid temperature cannot know when to limit operation to prevent overheating. Compare its reading against ambient after the vehicle has stood overnight — a cold-soaked vehicle whose fluid temperature disagrees with the air around it has an offset fault, and that is the failure a plausible reading hides best.
Typically a moderate job.
Codes this can cause (5)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0937 Hydraulic Oil Temperature Sensor Circuit Likely for this code Moderate
- P0938 Hydraulic Oil Temperature Sensor Range/Performance Likely for this code Moderate
- P0939 Hydraulic Oil Temperature Sensor Circuit Low Likely for this code Moderate
- P0940 Hydraulic Oil Temperature Sensor Circuit High Likely for this code Moderate
- P0941 Hydraulic Oil Temperature Sensor Circuit Intermittent Likely for this code Moderate
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