Mustang GT Shifting Problem Closed Transmission

There’s a known 2-3 shift problem with the Ford 5R55S transmission. Due to problems with the Valve Body and EPC solenoids, the internal pressure of this transmission does not remain within the parameters the manufacturer has determined are needed to keep the device on an even keel. Over time, wear in the Valve Body casting and composite sleeves protecting the servos allows the servos to lose their ability to apply the needed hydraulic pressure to the transmission’s bands. Instead of holding pressure firmly, the leaks let pressure drop so the bands back out, causing the problem.

In this situation, larger servos can take longer to fill if the overall hydraulic pressure picture in the transmission is low. The fix for this is having new end plugs and O-rings installed. The O-rings are installed on the low/reverse servo. This should fix the Valve Body problem.

The Electronic Pressure Control (EPC) solenoid/switch keeps track of your transmission’s hydraulic pressure. By regulating the pressure, the transmission can increase or decrease the amount of work the transmission does as the engine begins to work harder. The application of pressure means the powerteam (engine/transmission) works harder to change gears. The higher pressure also keeps the engine from hitting the redline.

The EPC module adjusts pressure by activating a hydraulic pump and changing the spring rates on the solenoid. It uses the pressure change to increase the amount of work the transmission must do to apply the clutch. The EPC monitors the airflow to the engine, engine RPM and throttle position to work correctly.

Though it may seem like the 2-3 shift problem is caused by low transmission fluid, it isn’t. Instead, it is hardware- and sensor-related. So, when you get your Mustang into the shop for work, suggest to the technician working on the car to look at these specific areas. Of course, getting to the EPC solenoid/switch does require getting inside the transmission so while it is open, it is time to replace other parts that might be worn, as well as the transmission fluid filter and transmission fluid. If you opt for this partial transmission rebuild, you are looking at a bill of anywhere from about $1,800 to $3,000, depending on exactly the amount of work you want done.

Although there is a known shift problem, I don’t think your transmission has been affected by it. The reason is that you can get to drive, but you can’t get the car into reverse. Instead, your transmission has gone into limp-home mode.

Limp-home is a fail-safe mode that keeps your Mustang rolling until you can get it to a shop. I would suggest that your next stop is a visit to your mechanic where he can put an OBD-II scanner into the diagnostic connector. The chances are very good that he will find a major transmission error code, possibly in the 0700 range. This range, P0703-P0784, is all the major transmission-related codes. There is one other general code that also pertains: 70765 which indicates a major transmission fault, but doesn’t point to any specific area. The others all point to specific parts.

Given the number of potential areas that can throw and error code and put your Mustang into limp-home, I strongly recommend that you have yours looked at right away. It is quite possible that the code may refer to a more minor system or even to an engine system (there are several systems that are shared between the engine and transmission) and may be just be a hiccup that can be cured by a system reset.

However, because you have already had a couple of episodes, I believe it is more serious than just a simple device error code. I suspect that your transmission may have had some damage done internally. The only way to find out is to start with the OBD-II scanner and move on from there.