I have no overdrive in a hi-mileage tranny. The electronic side including tps seem o.k.

I did pressure checks while test driving and found OD only had 20 psi.
Accumulator pressure is good in all gears. Stall is 2200rpm

Is this most likely a OD piston seal problem or a solenoid problem?
How do I test for either, or do I just buy both and replace them?
Also I understand there is a check valve that can cause problems, can I access this and change it by removing the OD section?

 

Use an ohm meter to check the coil on the solenoid. It should show low resistance(front and center wire). You can do it at the plug but it is hard to see what you are doing. It is easier to probe the wires a few inches from the plug. It is common for the small wire in the coil to break where it is soldered as it is open in the moving fluid. I have repaired a few by removing one turn of winding, scraping insulation and resoldering it to the terminal.

I guess you have hooked a test light to the OD wire at the trans and to a positive source of 12v and road tested. The light should light at about 40MPH. If not there is a computer or TPS problem.

The transmission Plug goes bad too. You can squeeze the terminals with a pic tool to make a better connection.

If these are ruled out it is an internal problem.

 

I checked the governor pressure and can't get any higher than 85 psi.

I hooked a test wire the the OD wire ( the brown one according to my schematic ) and it had battery voltage at all times even in park.

 

All three wires will show 12v when sitting still. The center wire is feed from the switch. That will feed through the coils to the other wires as the computer grounds them to lock OD and CL. Thats why I say hook a wire to the OD wire and run it in the cab to a test lamp hooked to a 12v source. The light should light at about 40 MPH. You can do the same with CL and it should come on at about 45 MPH.

 

I borrowed a scanner and read the 3-4 solenoid. It would only turn on if I held the OD switch.

I hooked a test light to the brown OD wire and it didn't make any difference if it was grounded or set to power source, with or without OD solenoid on according to scanner. Test light light does not light, and yes its a good light.

Live gauge on OD port only shows 20psi, I think it would be safe to assume the piston seals are bad, so would the clutches probably be burned up too?

would the bleed port / check valve for the OD cause this?