Trans issues

[Chevyrace01]

I have an 01 duramax I was driving home and I went up a hill and the truck just revd I stopped and put the truck in reverse and nothing then I let it coast down the hill backwards into a parking lot shut the truck off and started it back up put it in reverse and it works but just revs in forward gears the shift indicator flashes on forward gears have 4 codes for the trans any ideas what it could be

[DmaxMaverick]

Welcome aboard!

Check the fluid level. Add if low. "Up a hill" is a fairly strong indicator. If the level is up, smell the fluid. A burnt or acidic odor means the trouble is deeper within. If everything physical appears normal, then check the codes. Low fluid and/or slipping clutch(es) will toss a bunch of codes, so don't sweat the software until you check the hardware.

[Chevyrace01]

Welcome aboard!

Check the fluid level. Add if low. "Up a hill" is a fairly strong indicator. If the level is up, smell the fluid. A burnt or acidic odor means the trouble is deeper within. If everything physical appears normal, then check the codes. Low fluid and/or slipping clutch(es) will toss a bunch of codes, so don't sweat the software until you check the hardware.

I have checked everything over all fluids were full and red like theyre supposed to be none acidic smelling also had a bunch of codes went and changed the nsbu switch and now have no trans codes but truck still wont move in forwards gears only moves in reverse. sounds like the trans is junk or something messed up inside to me but any other ideas i can try before i drop $2400 on a new trans???

[DmaxMaverick]

Don't give up on the tranny yet. If it isn't throwing codes, it's probably OK. You just changed a major component, so maybe it needs a reset (yeah, I'm reaching). It may also need a filter service (external, control main spin-on filter --DO NOT forget the magnet!), so do that. Disconnect both batteries and ground a Batt+ cable to chassis/ground for 30+ minutes. This will clear any previous conditions/preventions. Make sure you're parked on level ground, check fluid level again (the "cold" level is approximate, check again when it's hot). Reconnect the batteries and try again. Restart several times if it doesn't improve. Check again for tranny codes.

[Chevyrace01]

Ok had batteries unplugged for 2 days only cause my work schedule I couldn’t work on it did what you had said and still no movement it feels like it wants to go starts moving then it stops and won’t do anything except in reverse which is fine but will keep trying to reset the system no tranny codes are pulling up only engine codes which are p0650 twice and p1643

[Chevyrace01]

Has anybody had this issue I don’t know if it’s a stuck valve or solenoids are junk or the trans is junk really getting frustrated and looking for ideas of what to do next

[Aerodyne]

My 04 LLY started to not go in reverse and cursor under the R would flash. over 1400.00 spend and found bad ing. switch sending low voltage to trans. Allison is very sensitive to voltage but GM transnot so much.

Lynn

[JohnC]

Not really. I had the same problem in my '95 except the only forward gear I had was second.

[Chevyrace01]

I started it up after replacing the nsbu and all trans codes are gone you shift it into drive and can feel it go in and rolls forward a bit then stops and just revs when I just shift it you can feel it go in gear and feel it and hear it change sounds like it went back into neutral or something and the same happens in all the lower gears as well but it’s fine when you shift it into reverse the truck moves but not in forward gears

[DmaxMaverick]

If you haven't yet, weigh the cost of a full tranny service (fluid flush/replacement and filter) vs. expensive repairs down the road. If a simple service cures it, it wouldn't be the first time.

Is your truck 4x4? If so, try low range. If the tranny clutches are worn beyond holding, but engage and seems to start to move, using low should shift near normal with the greatly reduced load. If it's 2wd, jack the rear axle and see if it shifts through the gears (watch the speedo, and feel the shifts, both manually starting from 1, and fully in D). If it works in low or with the axle jacked, then either the clutches aren't receiving enough pressure, the clutches are worn beyond service, or it has some other mechanical failure. Low pressure and/or solenoid failures almost always cause DTC's. You can also try a transmission additive to give the clutches a bit more friction and tighten up seals. I like Gunk TransMedic, and avoid Trans-X. If the additive works, it is a temporary solution, and the tranny is on borrowed time and headed for overhaul.

[flatstuff]

Range Shift Inhibited, goes into neutral and won't shift and the truck chimes at you: check out this vid, trans fluid in the TCM connecter at the trans

https://www.youtube.com/watch?v=fmNoPlqZthw&ab_channel=jaisantana

I will try and answer the question about how you get the plug off. Mine was coated in grime so first thing I did to see what's what down there I fully cleaned it by spraying simple green, scrubbing with a toothbrush and rinsing with water until all of the plug part was clean. The plug is actually the female part while the male part is attached to the transmission so the plug slips over the part attached to the trans and clicks in. Once it was all clean and I could see what's going on I inserted a 1" wide gasket scraper (a large flat blade screw driver will also work) in between the trans and where the bottom/end of the female plug almost meet, there is about a 1/16 gap. With one hand I grabbed the plug and pulled while I twisted the gasket scraper to help push it off from the bottom of the female plug part. It popped off without to much effort and it was full of transmission fluid. I disconnected the batteries and then spayed both plug and the pins on the trans side with electrical cleaner - I used a lot almost a quarter of a spray can and using the spray straw. Once I was sure both sides were clean and dry I put some silicon caulk into the small hole on the top of the female plug to keep fluid from entering there in the future. I added some dielectric grease to the female plug connectors and re attached. If I could have posted pictures here to show the plug parts I would have but I guess its not allowed.