I have a 95 GMC K 2500 7.4 with a 4L80E it has 151,000 miles, what happens is the vehicle is stuck in second gear and is setting the DTC 81, 82, 83, 85, 87. Also the instrument cluster randomly stops working, the tachometer and speedometer will drop to zero, get stuck at current position or bounce up and down, the shift position light will sometimes go dark and not notify what gear you are in. trans fluid is cherry red and no burnt smell. when it does randomly shift from 1st - 2nd which is very rare it is smooth. Shift to reverse is smooth. History of the vehicle is unknown due to the vehicle being bought at an auction. Have access to Alldata "friend from a Kia dealer lets me use his account" read all about the faults and some of wiring tests before I start tearing into this just wondering if anyone has had some similar problems or seen anything like this, Thanks for the help!

I would check the basics before tearing in to anything too intense. Look for major wiring faults, also check for corrosion at major power and ground points. A bad battery/alternator can also cause very odd things.

If nothing pops up, I would first throw another PCM at it, especially if you can get one inexpensively at a salvage yard.

These codes are all over the place, which is why I am not quick to start throwing other stuff at it.

Codes, because it took me a minute to find them:

https://www.troublecodes.net/gm/gm-j...vandura-yukon/

Actually, I was looking at a different list when I first posted, which mentioned EPROM issues on one of the codes.

Now that I look at it again, a lot of it is screaming that it could be speed sensor issues. That doesn't explain why the instrument cluster freaks out though. If anything, it would just make the speedo only do weird things, the tach should remain consistent.

I stand by the Power/Ground check recommendations. Also don't be afraid to check ignition switch and key on relays. Some of the codes my Olds popped with a bad battery were VSS related. Bad power/ground causes nasty gremlins.

Thanks for the quick reply I need to update some of what I found. I started popping off dash pieces just to inspect the harness and the instrument cluster for any melted wires etc.. and sure enough I found some melted wires on the dimmer switch circuit. I repaired those wires and test drove the vehicle the dash does not do anything weird, neither does the tach now but the speedometer still will act up. the speed will drop to zero then jump up back to speed or whatever it sees fit.

I am with you, from my research I learned the PCM grounds all the solenoid circuits and the ignition switch supplies all the power to those shift solenoids. I learned that DTC 81 and DTC 87 default to 2nd if they see any problems. so the commons I am seeing are ignition switch because if DTC 81 shorts to power it defaults to 2nd, vehicle speed sensor because of the speedometer acting funny and DTC 87 defaults to 2nd if it sees a problem which can be set by a speed sensor failure, or powers and grounds at the PCM because the PCM grounds the solenoids for operation. no work tomorrow, so I will get checking things tomorrow. Have worked on a lot of cars, but this one is definitely a head scratcher.

Also the battery is a year old according to the sticker, and the alternator looks relatively new. I apologize for the huge font on my first post that was my first time posting and for some reason could not figure out the font lol.

Never assume a component is good because it'* fairly new.

I think you are on the right track, check basics and then focus on the vss

Another update, it was cold this morning so i was not feeling like laying on the cold concrete underneath the truck so I checked all fuses with my power probe and all looked good. I decided to clear all the DTC'* and drive it to see what came back. Fired up the truck drove down the street sure enough shifter from 1st-2nd smooth then shifted from 2-3 smooth, I pulled over turned off the truck and checked codes it first came back with a DTC 83 TCC PWM turned the vehicle on and then drove home and nothing but 2nd the whole way this was less than .10 of a mile. The shift indicator light was on and off the whole drive. When i got home and pulled into the driveway checked codes and had DTC 81 2-3 shift and DTC 83 TCC PWM. So I pulled the wiring diagrams and found this,


These two solenoids receive power from the ignition switch on the same circuit, Circuit E but they have their own individual circuits from looking at the transmission connector pinout. the ground as you can see from the diagram is grounded by the PCM but on completely different circuits. So my gut says the problem is likely occurring on the Ignition switch circuit or the ignition switch itself. It seems less likely that all the ground circuits to the PCM have failed. Still is possible that the PCM is failing but that would mean all of the ground drivers for the trans went at the same time which is possible but does not feel as likely as the one feed circuit from the ignition not working. But that still leaves me confused as to why the tach, the speedo, and the shift position light glitch out. I am going to research what powers on and controls the tach, the speedo, and that shift position light and see where that points me I feel like they are all sort of related because the DTC 87 high ratio error will set after it takes its input and output speed sensor ratings compares it to its known value for a particular gear that is selected. So if i select gear 3 but it wont shift out of second and I go 60 which I have done I believe that would trigger this particular fault. Or, when the shift indicator light goes out maybe the PCM is confused on what gear it is in and then this fault is trigged along with DTC 85 undefined ratio error. I will update after I search on the tach speedo and shift position light.

Fair enough Ill do a test on the battery and see where that gets me.

sorry see *what* that gets me.