2019 GMC Yukon NO Trans Gears, NO Tachometer, NO Oil Pressure, NO Power Steering SECOND TIME!

BlaineBug · February 22, 2020

It is obviously apparent that TSB # 18-NA-161 was NOT the fix for this problem. Which is what I assumed from the beginning, considering that the last time they claimed to not find anything wrong. Issues don't just resolve themselves without any external input to rectify the issue. Here's to wishful thinking that General Motors will take the issue more seriously this time........but I'm just awaiting the typical response of "could not duplicate customer concern" to rear its ugly head again!

Edited February 22, 2020 by BlaineBug

BlaineBug · February 28, 2020

I received a call from the GM service center today saying that a new ECM has been ordered. I inquired how they were able to determine that the ECM was the culprit but was told by the service adviser that they will have to get back to me on that. I will update again when I hear more.

BlaineBug · February 28, 2020

I received a call back from the dealership about the ECM replacement and they told me that the technician coordinated with General Motors technical support and that replacing the ECM was at the suggestion of GM because "that's the only code they were getting." I don't know what code they were getting this time, however, the last time I had the vehicle towed in January, the three history codes that they said were present (according to the service invoice) were the following;

1) U0100 (Lost Communication With ECM/PCM "A")

2) U0121 (Lost Communication With Anti-Lock Brake System (ABS) Control Module)

3) U0422 (Invalid data received – body control module)

So basically this sounds like somewhat of a guess because they told me "we'll replace the ECM and go from here."

carnau · March 4, 2020

Hey BlaineBug. I have read all of the posts on here and some of them have me questioning things. For instance the first time it was brought in and the codes were checked. It shows how many miles the vehicle has been driven since the DTC was set. So if it was towed, it should have been low. I wish I knew what those codes were. They could help.

The last set of codes you posted. Do you know which module set those codes? For instance did the Transmission control module set the U0100 saying it couldn't communicate with the ECM/PCM. Without knowing which module set the codes it doesn't really help me. They can actually give you a printout from GDS2 on the codes set. If you could get me those and post them here I can continue to help.

Unfortunately fixing a vehicle while it is working properly is one of the hardest things to do... But it can be done. You can manipulate wiring, and using the codes in the vehicle and the data schematics atlest pinpoint where the problem is evolving.

I really only have a small piece of the puzzle at this point with the codes that you posted. But if I had to guess they are going to replace the ECM, if that doesn't fix it they will replace the wiring from the TCM to the ECM and if that doesn't fix it they will replace the TCM. Again, I am only guessing this because I am guessing the TCM is the module setting the codes and since it is the live module between the ECM and the EBCM (ABS Module) and the ECM is the terminating resistor for the GMLAN it would be the quickest and easiest thing to replace.

Again, I am only guessing because I don't have all the information I need. If you could find out which module is setting the DTC or even better get the GDS2 DTC report printout for me I can really help you a lot more.

Hope this helps.

BlaineBug · March 4, 2020

I can't tell you for certain which modules were setting those three stored codes the first time. I also had no check engine light but they claimed that those three codes were history codes and that they didn't mean much. I know the service advisers aren't techs, but he said that since they were history codes they could have been created whenever.

This second time I have yet to find out what code was being stored for certain but over the phone the service adviser said that the only code that they had pointed at the ECU. But in-between the two visits to the GM service center I did remove the battery to have it bench tested so I wonder if that would have unfortunately stored a code that they are misinterpreting as being related to this second occurrence. There were a couple of people suggesting that the battery was bad but I did my due diligence and had it tested three times by separate parts stores, and the last time like I said I pulled the battery out to have it tested out of the vehicle. Tested fine each and every time.

And yes, they have replaced the ECM at the advice of GM TAC. Out of curiosity, what would the transmission control have to do with having to press the "start" button a second time to get the gauges, infotainment system, and HVAC controls to illuminate, even though the engine starts on the first press? It is somewhat reminiscent of remote starting the vehicle and getting in before you put your foot on the brake and press start to gain access to the vehicle, but not quite the same.

Edited March 4, 2020 by BlaineBug

carnau · March 4, 2020

12 minutes ago, BlaineBug said:

I can't tell you for certain which modules were setting those three stored codes the first time. I also had no check engine light but they claimed that those three codes were history codes and that they didn't mean much. I know the service advisers aren't techs, but he said that since they were history codes they could have been created whenever.

This second time I have yet to find out what code was being stored for certain but over the phone the service adviser said that the only code that they had pointed at the ECU. But in-between the two visits to the GM service center I did remove the battery to have it bench tested so I wonder if that would have unfortunately stored a code that they are misinterpreting as being related to this second occurrence. There were a couple of people suggesting that the battery was bad but I did my due diligence and had it tested three times by separate parts stores, and the last time like I said I pulled the battery out to have it tested out of the vehicle. Tested fine each and every time.

And yes, they have replaced the ECM at the advice of GM TAC. Out of curiosity, what would the transmission control have to do with having to press the "start" button a second time to get the gauges, infotainment system, and HVAC controls to illuminate, even though the engine starts on the first press? It is somewhat reminiscent of remote starting the vehicle and getting in before you put your foot on the brake and press start to gain access to the vehicle, but not quite the same.

The Transmission control wouldn't have anything to do with it. What it is doing is saying there is a problem in the High speed circuit. The High speed GMlan is a Communication circuit. It has to communicate across the whole thing for any of it to work. So your vehicle works like this.

ECM (120ohm) - TCM - Transfer case module - gateway module - body control module - power steering module - suspension control module - park brake module - chassis module - 120ohm terminating resistor

The DLC (where you plug in a scan tool) is located between the gateway module and transfercase module. It uses terminals 6 and 14 to communicate. If you tested it with a multimeter you would have 60ohs (the two 120 ohm resistors in the system give you 60 ohms.)

When you are having this issue you do not have 60ohms. There is a break in the communication. (That is why you have U codes in the vehicle)

So the system is testing itself and it sees the last module working is (and like i said I am guessing) the TCM. So the TCM sets the codes saying it can't communicate with the ECM. Since it can't communicate with the ECM (and the ECM has a 120 ohm resistor made into it) now the whole system is reading 120ohms and nothing can work right. This is why you're getting all the messages, your vehicle won't hardly move ect.

This can be caused by either a bad component or bad wiring. The codes if read right can tell you that the problem is between (BLANK) and (BLANK). Lets say its between the ECM and TCM. So either 1 of the 2 modules are bad or the wiring is bad. First you would manipulate the harness and try to get it to fault the system out. Just like hitting a bump or shifting the vehicle into park and the engine rocking moving the harness just enough to cause a fault. You would also look for breaks in the wiring or poor terminal crimps or poor terminal tension. If all the wiring checks out (voltage drop test ect.) then you replace the component that lost the communication. In this case it is the ECM because another module is saying it couldn't talk to it. The module that's trying to communicate is working fine. There is a very very very very very small chance that it could be the problem but not likely. This is why you would replace the ECM. Then if the problem returned, replace the wiring and if again the TCM. Normally before it gets that far you have located a bad wire,terminal or crimp, in the initial testing or the component you replaced fixes it.

BlaineBug · March 4, 2020

Thank you. I'll see if I can get more information about which modules were setting the codes. Is it possible they would be able to look back to January 13th's episode as well? I'll find out.

Edited March 4, 2020 by BlaineBug

carnau · March 4, 2020

4 minutes ago, BlaineBug said:

Thank you. I'll see if I can get more information about which modules were setting the codes. Is it possible they would be able to look back to January 13th's episode as well? I'll find out.

The original dealership and the original tech that looked at it the first time could pull up the old codes in GDS2 if the laptop he is using has not been replaced. It keeps session logs you can go back to and will show everything the tech did (reading data, reading DTC's and clearing dtc's) But... it is very complicated to do unless the tech has done it before. It's not done a lot. But it is doable.

BlaineBug · March 4, 2020

I did my best to find out through the service adviser and was told that "this information or print out would not be possible since the new ECM was already installed" and when I asked which module was giving the code for failure to communicate with the ECM, I was told "Unfortunately it was just a generic code for lost communication with the ECM and did not state where it originated from."

Which doesn't sound truthful from what you're telling me they should be able to easily pull up. I'm hoping this code wasn't set when I removed the battery to be bench tested, although that was a good month ago a least. That would be a real b1tch if it was.

Edited March 4, 2020 by BlaineBug

BlaineBug · March 9, 2020

Got my Yukon back today after 17 days. The ECM was replaced as previously noted, but one additional item that was found was that ground #141 was found to be full of undercoating. I'm not exactly sure what that means or where that ground is but it was my understanding that the frames were waxed. Regardless, I'm not sure why they are still mentioning TSB 18-NA-161 which is what they supposedly completed the first time in January.

Still mentioning that the only code found was U0100 for "loss of communication with the ECM." It was from the advisement of GM TAS that the ECM be replaced, so that's what they did.

Edited March 9, 2020 by BlaineBug

jimboinfl · May 16, 2022

BlaineBug,

Did you ever identify what the actual problem was? Was it the ECM or something else? I have a 2019 GMC Yukon XL Delani that did something similar (the control panel started showing everything failed and the transmission would no longer move, although the engine would keep running).

Jim