What does it mean?
The transmission or transaxle hydraulic pump pressure is controlled (See above animation) by a PWM (pulse-width-modulated) solenoid called: TFP (Transmission Fluid Pressure) solenoid, EPC (Electronic Pressure Control) or PCS (Pressure Control Solenoid), VFS (Variable force solenoid), or just FM (Force Motor). This solenoid is NO (normally closed), which results in high regulated pressure (see above animations) is not open and regulated.
About 1 amp of current will allow the solenoid to open, to reduce and regulate the hydraulic pressure. This pressure solenoid is PWM (Pulse Width Modulated) so the higher the duty cycle, the more current and the lower the pressure and the lower the duty cycle, the less the current, the higher the pressure. Duty cycle is the on time of the solenoid versus the off time, so a 90% duty cycle represents that the solenoid is on 90% of the time.
The EPC replaced the old mechanical pressure regulator valve. DTC P0745 sets when the transmission fluid pressure solenoid malfunctions, in most cases the problem is not the electrical part of the solenoid; the problem is generally foreign material obstructing the mechanical function of the solenoid or the flow of the fluid through the transmission valve body.
The line pressure solenoid valve regulates the oil pump discharge pressure to suit the driving condition in response to a signal sent from the TCM (Transmission Control Module) or PCM (Powertrain Control Module).
NOTE: When you find a 700 series transmission/drive line DTC (Diagnostic Trouble Code) with your scan tool, you must also check for other DTC series like Chassis (C-codes), Communication (U-Codes), and Body systems (B-Codes), not just under “P” or powertrain codes, which include engines and transmissions/transaxles. These may not show on a generic scan tool. DTC P0745 sets when the PCM/TCM has detected an problem in the electronic pressure control solenoid circuit.
Computer controlled automatic transmissions use variable amounts of hydraulic pressure to provide shifting and TCC (torque converter clutch) operation. Figure 1 shows a simplified wiring diagram of a TFT circuit. Figure 1 Trans Fluid Pressure Control Circuit