Help - Codes - U0100 & U0073

[olskool]

Need some help here. We have been dealing with the CEL on with the Code U0100 present. If we clear then code comes back. After some internet searches it was suggested that we install a 120 ohm resistor. We believe the code is related to the TCM as right now it will not shift - 6L80E transmission. So, we installed the resistor and what do you know, the CEL stayed off and didn't come back on. However, it wasn't starting properly now. Did some more internet reading on this issue and it was recommended that we install 2 more 120OHM resistors. Well, that lead to the U0073 code and now we can't get rid of that one. We had found while searching to install another 120ohm resistor but then we were not able to access all the PIDS, only a few. That's when the U0073 code showed up. Removed the resistors and the U0073 is still present but we are able to access all PIDS now. We can read and write. But - CEL is back on for the U0100 code again. We can drive this around the block but no shift. It runs excellent by the way, idle is great, nothing seems out of the ordinary except the U0100 code and no shift. Like it's a limp mode. Any thoughts on this?

[gtstorey]

There should be two 120ohm resistors in parallel in the the data circuit if that is where you are talking about adding them. Start with this;
http://resources.aeswave.com/ATG-05_...%20may%20occur.

See the test on page 3.

I think typically one of the resistors is at one end of the chain in the ECM and the other is sometimes in another module such as the electric power steering module and sometimes just a resistor in the wiring harness near the DLC.

[olskool]

Ok, we ran the test on Page 3 of that. We have a reading of 120ohms between #6 & #14. It should be 60 OHMS, correct?

[gtstorey]

Yes it should be 60 ohms.

Is this a swap vehicle? Do you have a wiring diagram? Some of the GM diagrams show where the resistors are located in the modules. I removed the EPS from my 09 Cobalt kit car that had a resistor in it and it made communications iffy but would sometimes still connect about like you describe. It would sometimes run (poorly) and sometimes wouldn't start. I put a 120ohm resistor in its place and its been fine since.

At this point you know you have one resistor but can't really tell which one it is. It could be the first one and the data line is broken after it or it could be the last one and the first one is missing. The data network is like a ladder with each module a rung of the ladder. At the top is the data link connector (actually the comms device) second rung down is a module with a resistor or just a resistor. Below that are the other modules as rungs (rungs being devices in parallel) and at the bottom rung is typically the ECM containing a resistor. You can remove the intermediate rungs (with the appropriate rewiring to connect up the sides of the ladder) but the ones that contain the resistors have to stay in place or at least have the resistor put back in place.

[olskool]

Ok - 60 ohms. Yes this is an LS swap. 6.0L with 6l80E in a 1958 Cadillac. Now, it will not start. We have been experiencing this from time to time. Then it will start and run no problem.

[gtstorey]

Sounds like it might be intermittent connection on the data path. What modules are left from the original donor? Although I said the modules are the rungs of the ladder, typically (maybe always) the sides of the ladders are actually made up inside the module.

[olskool]

There are no modules left.

[gtstorey]

Ecm/tcm?

[olskool]

ECM and TCM are in the same unit. 1 plug each

[gtstorey]

I thought all 6L80E had a built in TCM. Is this a connect and cruise setup?

[gtstorey]

You should probably just go ahead and add as much info about your build as possible vs one post at a time to individual questions.

[olskool]

Yes - the TCM is built in the PCM together. It is supposed to be a connect and cruise. We have driven it but it would not shift out of 2 gear(I Think). We drove it around the block. Everything was fine with the engine. Tune was good, etc... Just could not get the CEL off. That's when we started to dig into this issue and we came across the resistor idea. The harness is a stand along harness for the engine and transmission with a separate fuse/relay panel that we join with the chassis harness. What other information do you want to know.

[gtstorey]

I don't know that I'm going to be much help since I don't have any experience with the connect and cruise other than saying everything I see online indicates a separate TCM.

I would guess that the 120/60ohm test is still valid, but that's purely a guess. If it is supposed to have the 2 x 120 ohm resistors, I have no clue where they might be on the connect and cruise harness/modules.

[blindsquirrel]

If the engine computer and transmission computer are all in the same box, then that is a "PCM", and if it's a PCM it's not a Gen 4.

Not the first time this has been asked here: What are you working on?

What is the ECM/PCM/whatever? What is the tune file in it for - year/make/model? Do you think it would prevent a bunch of this guessing and vague suggestions and questions back and forth if you would post the tune file for the thing you're working on?

[GHuggins]

My only experiences with these having the auto's is with the 4l65e's, so I went and checked out the specs for the 6l80 combo. Looks like it's just like the 4l's where it uses a separate SuperMatic transmission controller and associated wiring to control the transmission. The ECM is then programmed as a manual and the transmission controller has to be separately programmed by itself. Might want to check that part of it is working and powering up. You might even want to contact who you got the kit through or GM Performace - if there still is a thing and see what they have to say.

OP - Do you have this setup? Agree with Squirrel, a posted file would help with the confusion.

[olskool]

This setup is in a 1958 Cadillac. The engine and transmission are from a 2018 Chevrolet Express Van. It's a 6.0L w/6l80E transmission. Now, don't go all crazy and tell me it's not an LS 6.0L. Yes it is. GM used the LS 6.0L engine in the Express vans until 2019 I believe. Trucks and others switched to the LT engines around 2015. We learned this in the very beginning of this project. The PCM is a factory unit. I will get a picture of the part number and post later. What GHuggins stated is what I'm thinking about doing is going with a separate transmission controller. Good way to solve this issue possibly but it's a work around. I am really trying to figure out why this is happening for future reference as other have done a LS 6.0 w/6l80e without problem. What have they done and not have problems.

[blindsquirrel]

I still do not see a tune file posted.

[gtstorey]

You do not have a connect and cruise then and you have a controller in the transmission. To me this puts it back to missing one of the two 120 ohm resistors it should have or a wiring problem that leaves one of them out. When you added in a resistor where and how did you install it?

[blindsquirrel]

If you never post the tune file, you'll never get an answer that's any better than guessing. Nobody knows what ECM you have yet, and you need to get the hardware/service number off the TCM if you don't already know it. Not all OSes are compatible with all hardware, and not all ECM OSes are compatible with all TCM OSes.

[Shrek]

ECM and TCM are in the same unit. 1 plug each

No - not remotely correct regarding a 2018 6.0L (Gen 4).

... Yes - the TCM is built in the PCM together...

No - not remotely correct regarding a 2018 6.0L (Gen 4). These have an ECM (engine control module) and a TCM (transmission control module).

... The PCM is a factory unit. ..

No - not remotely correct.

You have an ECM (engine control module) and a TCM (transmission control module).

You do not have a PCM (powertrain control module).


A 2018 Express van will have an E78 ECM (Blue, Black, and Grey connectors).

If your ECM has only two connectors (Black and Grey) then it will likely be an E38 - which was used by Express vans between 2008 and 2015.

The TCM is inside the oil pan of the 6L80 / 6L90. There is a large round TCM connector on the passenger side rear of the transmission.

A U0100 DTC is often indicative of an OS (operating system) mismatch between the ECM and the TCM.

Is the ECM from the same donor vehicle as transmission ?

If not, this is most likely the issue.

Regarding adding resistors on the communications bus - this is completely unnecessary as long as the ECM is connected to the communications bus - it has the requisite internal resistor.

Your posts indicate that you do not understand the control platform of your project.