P0939: Hydraulic Oil Temperature Sensor Circuit Low

What does P0939 mean?

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.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Gearbox warning or overheat message
• Reduced performance or altered shift behaviour

Common causes

• High Sensor signal wire shorted to ground
• Medium Temperature sensor shorted internally
• Low Control module input fault

Likelihood is a general estimate across vehicles; your make and model may differ.