| Transmission fluid pressure (TFP) solenoid circuit malfunction
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|Wiring, TFP solenoid, ECM/PCM!TCM
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Table of Contents
- What Does Code P0745 Mean?
- What are the common causes of code P0745 ?
- What are the symptoms of code P0745 ?
- Codes Related to P0745
- Get Help with P0745
What Does Code P0745 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
What are the common causes of code P0745 ?
- Low, dirty or contaminated transmission fluid If the transmission fluid is very dirty, it is recommend changing the transmission fluid and if possible removing the transmission pan for further diagnosis.
- Excessive debris or metal particles on the transmission pan could be an indication that there is a transmission mechanical failure and that the transmission will need to be rebuilt or replaced.
- Defective pressure control solenoid
- Line pressure solenoid valve harness is open or shorted
- Line pressure solenoid valve circuit poor electrical connection
- Fluid blockages inside the transmission fluid passages
- Mechanical internal transmission failures
- Defective PCM or TCM but this is rare
What are the symptoms of code P0745 ?
- MIL (Malfunction Indicator Lamp [Check Engine & Service Engine Soon])lights on with stored historical P0745
- TCC does engage/disengage
- Disabled shifting function with engine stall when coming to a stop
- Harsh shifting, transmission slippage, transmission overheating
- Fuel efficiency concern
Codes Related to P0745
- Transmission slippage codes often accompany this code like DTC P0894
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