Well, I'll try again! Just got done writing a long post to reply to your problem and had a power failure right as I was ready to post it!!!!
To make it shorter this time, there are two systems to supply air for the tool changer. One supplies the air to move the piston up and down and another to slow the movement. This is so the piston does not slam down violently, and very noisily.
If you check the incoming line at the top of the piston/cylinder, you will probably see two lines coming into the top. One supplies the air to move the cylinder and the other line supplies air to slow the pistons movement, or the air incoming to move the piston.
There is a small piston inside the T-fitting that is moved by the resistance air to restrict the incoming air for the piston. As the pressure inside the piston starts to rise the air from the resistance side is overcome by it and full pressure arrives in the cylinder and it reaches full pressure and distance.
If the valve/regulator for the resistance air sticks (which our machines' did) it will prevent the tool change system from reaching full height because it keeps feeding air to the top of the cylinder and will cause a tool changer error.
If you feel comfortable doing it, I would remove and disassemble and clean the one for the resistance first, then the other if it does not fix it.
This is very difficult to explain, so let me know if you understand.