Diagnostic code P0748 OBD2 is established at the time the PCM (Powertrain Control Module) finds a fault in the transmission pressure control solenoid. The solenoid aims to regulate the transmission flow pressure, ensuring efficient transmission operation in every gears.
When initiating a gear change, the pressurized fluid is diverted in each hydraulic circuit by the solenoid, maintaining the pressure required to keep the clutches and the gears engaged. If the pressure is not sufficient, the transmission may slide, while if the pressure exceeds the limit, the transmission may overheat and components of the transmission may be damaged.
In order to maintain the pressure of the transmission fluid within the given range, the Powertrain Control Module constantly monitors the actual fluid pressure at various operating parts in the transmission, then compares the reading obtained with the wished pressure. If the PCM finds an electrical fault in the solenoid control circuit, causing the actual pressure to be delayed from the set pressure, this code is set and the Check Engine light is illuminated.