18, 8 speed, power, ground, serial, MIL, temp.png18, 8 speed, pressure and shift solenoids.png18, 8 speed, speed, internal mode switch.png18, 8 speed, tap up down.png
Here are most of the 2018 Yukon 8L90E schematics.
18, 8 speed, power, ground, serial, MIL, temp.png18, 8 speed, pressure and shift solenoids.png18, 8 speed, speed, internal mode switch.png18, 8 speed, tap up down.png
Here are most of the 2018 Yukon 8L90E schematics.
Last edited by IARLLC; 01-08-2020 at 02:10 PM.
Here's more info from HPTuners themselves. maybe we can make this a FAQ for anyone else in the future..
Question: Alright how about if I have a T87A that came from a 8L90E donor car and I
am trying to use it with a 10L90E. Can I have the TCM unlocked and loaded
with 10spd info? And you guys put my vehicle vin on the TCM as it needs to
match in order to communicate ?
Answer (HPTuners): As long as the service part numbers are the same for both vehicles you would be able to do that. For us to program it has to be a compatable TCM for the base calibration file to work.
as of right now from my understand and waiting back on confirm from them, there are only 2 compatible service numbers for the T87A. Service #24279973 or #24289543
"so your basically saying its all the same"
Well the TCM connector is the same and a number of the wires are the same (color/purpose) but some of the wire colors/purpose are different. The TCM pin-outs have all the info you need to convert your 8 speed harness to a 10 speed. You can pretty much just pin the 10 speed trans harness in at the TCM connector.
Last edited by IARLLC; 01-08-2020 at 03:12 PM.
Transmission is Ordered! ships out tomorrow.. no turning back now lol 2018 Yukon 10L90 with 1,200 miles..
This is awesome! Are they sending you the harness or at least the trans part of the harness?
No lol just trans/converter.. truck was dismantled and gone.. god knows what they did with the harness.. I'm still waiting to hear back from the swap harness guy about making me a harness.. he said at the ECU its different.. but if both a T87 and T87A can be swapped around with no issues would really lead me to believe I can just make a jumper at the tranny plug and that's it. It's not like I'm missing any wires. Heck the 8l90 has 27wires and 10l90 has 26wires from what I was told. I have to print out those charts u gave me and examine it.
Was it just me or did u say that both plugs have the same order of pins and both even share the same inputs.. I dont even see much different other than just make an adapter harness and keep the pin order the same..
I did not see if the plug at the trans is the same. For whatever reason I did not find the actual plug diagram for the 8 speed. If the plug is the same (doubt it), there are only a handful of wires to switch over at the TCM. They are detailed in post #39, second scan. On the far right you see M5U or MF6. The places that you see those 2 options are the places that have differences, M5U for 8 speed and MF6 for 10 speed.
If the plugs are different, you could cut up at the TCM or down at the trans to connect your 10 speed plug. That TCM schematic is enough to connect it all.
The plugs are different.heres pics of the 8l90 trans plug. 8L90E_1.jpg8L90E_2.jpg
ok well I have the 10L90 plug & 8L90 Plug on their way. ill work on making the conversion harness. Im really on my own now..
"I don't have any idea if that is going to work. I don't know how to swap a 10 speed transmission into a vehicle that originally came with an 8 speed and get everything to work properly I have never done it and no one in the office has any idea if it will work." - HPTuners
how is the swap coming along????
Gathered a ton of new info.. programmed my own TCM and have everything ready to go. have to make a conversion harness. Might actually tackle it all within a few hours..
will take pics and document the process and will report back here how it goes lol
So i said screw it and started it on friday.. its all done but i cant seem to get tre transmission to do anything and i know why, i have 3 wires that on the 2018 come from the ecu and are 5v sensor power and ground, so thats all i have left.. I cant seem to find any ECM pinout schematics for the 2018 E92 to confirm what they are, but the 2018 TCM diagram does tell me. so im working on that now..
the ones in question are at the TCM plug.
#6 - ignition mode switch mode control backup (seems to be a swithed 12v signal from ecu) to pin X2 67
#12 - transmission pressure sensor A 5V Reference (5v power) to pin X3 18
#20 - IMS mode switch low Reference (sensor ground) to pin X3 19
Last edited by chameleon; 02-03-2020 at 02:53 PM.
Okay guys.. seems like y?all are on my topic. I have a 2016 GMC Sierra 4x4 came with l83 and 6l80 trans. I?ve put on lt4 blower and cam more and decided to swap to 8l90 to stay in my powerband better. 8l90 trans, engine/trans harnes, Tcm, matching transfer case Everything is installed. Now I need to know what has to be done programming wise to make this work. I have reflashed the bcm, cluster and Tcm with a truck same year with 8l90 and because ecm and bcm vins don?t match it won?t start. Not even sure I needed to touch bcm in the first place but I did and now I?m here lol
Can I just reflash everything back to stock minus the Tcm and cluster? And this should work right?
This is a perfect combination if you asked me. Gonna be awesome!
Here are some facts that I have personally seen and done:
Actually the BCM vin does not have to match. I take care of a fleet of 2017 Denalis (outside of the US) that GM refused to allow a certain change that the owner required. So I flashed all 42 of them to a vin that was the exact same options except for the one that the owner cared about. I will not affect starting unless you used one that had a different key (blade instead of smart) style. Maybe that might conflict.
If you change the BCM vin your radio locks and your odometer quits until you flash them to the same vin. If you drive more than about 25 miles without flashing the cluster to the new vin the odometer is a pain to get back to life...but possible. Backup sensor system won't work with BCM vin changed. BCM, Cluster, and Radio have to have matching VIN but it does not have to match your rig.
TCM does not have to match vin. As you have seen in the above posts, a TCM from the same configuration will start and run normal with a wrong vin.
Why is yours not starting? Possibly different key style? Not sure. Maybe the PCM needs to be flashed to a compatible OS to work right with an 8 speed TCM. I am really leaning that way. I would probably run full diagnostics on the system and see what it can tell you. I've read that 6 speed rigs won't work when you change TCM/trans until they are married to the PCM. I don't know the details of that. Maybe people say that if the TCM arrives empty but I have installed a 6 speed from a 2008 into another 2008 rig without having to "marry" them. I still married them but not until after I drove it around to be sure that I really did not have to. My thought in your case is just that your PCM OS needs to be swapped to an 8 speed OS. When you flash the T87, 8 speed TCM with SPS you have the option of flashing together with the PCM...which in your case might complicate things. Will be great if you can just do an OS change. Hope so.
I'd also be curious to jump the starter solenoid and see if everything else works. And if you plan to leave the BCM and Cluster at the new vin, I'd flash the radio to that vin as well.
Last edited by IARLLC; 01-04-2021 at 04:06 AM.
This is very great info!! I really really really appreciate it man.. I?m telling you I?m looking for all the information I can find on this, I?ve never been this persistent on a build. The truck is already 600whp and pulling like 3.4/5 0-60 in awd launch, so I?m dying to feel it with the 8 speed
So I believe I have the wrong harness, I believe it?s for something other than my truck, there?s a couple wires that are not in the engine harness going from the ecm to fuse box, and run crank 1 circuit, we?ve got the truck to where it will try to crank but won?t start. Have this one circuit to chase down
Well even if the answer to the riddle is a painful one it is still awesome when you find it.
I was going to mention that I have seen a swapped TCCM cause a no start initially but after the adaption process it works fine. The adaption can be done with the nob or GDS2 but if it is the original TCCM and it has always been used on that transfer case it does not need anything.