Allison 5sp: Codes set P0847 & P0872

[dmaxmo]

I changed the fluid and spin on filter in my truck and after the truck was started the transmission made a clunk and the service engine soon light came on. Tranny is in limp mode. Checked for codes and found P0847 & P0872 were both present. Reset the codes and restarted the truck and put tranny in drive. After a few seconds transmission popped again and both codes came back.
P0847 is Trans pressure switch solenoid D circuit stuck closed
P0872 is Trans pressure switch solenoid E stuck closed
I replaced the NSBU switch thinking it could be the culprit but after replacing the switch and clearing the codes they came right back as before.

Any ideas or suggestions will be very much appreciated!
Darrell

 

[messejme]

sounds like shot washed into the selenoids. how dirty was the fluid? mayhave to pull the selenoids and orvalve body to clean.

 

[Mike L.]

Time to pull the pan and check wires and filter.

 

[dmaxmo]

The fluid looked a little dirty to me and filter magnet had a good collection of material on it. The fluid was/is Transynd and looks a little darker than I thought it should be.

 

[dmaxmo]

Time to pull the pan and check wires and filter.

Mike,
What should I be looking for when I drop the pan besides the electrical connections?
Darrell

 

[Mike L.]

You have not givin much info here. Remember we can't see or know what you know.
Was the pan dropped during your service and filter changed? need history on trans. Built or stock? How was trans treated? How many miles?
Look at connections inside pan. Look for trash at bottm of pan. How much metal on internal magnet at bottom of pan? Finaly, peel the filter apart and unfurl paper element and see if there is trash in there.

 

[dmaxmo]

You have not givin much info here. Remember we can't see or know what you know.
Was the pan dropped during your service and filter changed? need history on trans. Built or stock? How was trans treated? How many miles?
Look at connections inside pan. Look for trash at bottm of pan. How much metal on internal magnet at bottom of pan? Finaly, peel the filter apart and unfurl paper element and see if there is trash in there.

Mike,
Ok...here's more info. The transmission is stock with 167,000 miles and the pan has never been off of it so the internal filter is the original. The truck has mostly been a daily driver but has seen some occasional towing and has had the Diablo Sport Predator towing tune for most of its life. Fluid and external filter changes as needed. I did find the transmission dipstick tube broken recently so I guess there is a possibility of some contamination going down the tube while it was broken. I removed the tube and tigged it back together and re-installed it the same day I changed the fluid and filter. The filter magnet was pretty much covered with black material.

Thanks for the guidance so far and I will drop the pan as soon as I can.
Darrell