Ethernet issues

Caleb Technician Indiana Posted   Latest   Edited  
Case Study
Network Communications
2019 Chevrolet Equinox LT 1.5L (V LYX) 9-spd (9T50)
U1884 Lost Communication With The Radio On The Ethernet Bus

I recently has this low mileage 2019 Equinox with a customer complaint of the radio screen intermittently going black and loosing audio and then coming back within a few seconds. The customer was waiting for diagnosis so I was under the gun. I couldnt duplicate the concern at first. I plugged in GDS 2 and did a full module scan. I only had this code and it was history. 


U1884 was stored in the Telematics Communication interface module. The description was it had lost comm with the radio on the Ethernet bus. The Ethernet bus is only between the radio and the Telematics. Its just a 2 wire network. I searched for TSBs. I only found 1 that said this code may lead to replacement of the Telematics Communication Interface Module but to proceed with normal diag first. I was in a hurry and really needed to duplicate the concern. The Telematics module is behind the radio screen and was not easy to access. The radio however is very easy to access between the HVAC case and the pass. A pillar. The LVDS cable transmits the video and graphics data( along with other info above my pay grade) from the radio to the radio screen. I unplug the LVDS cable at the radio and the screen goes black. Okay cool that just helps me get a sense of direction for the complaint. However the audio is still playing. The Ethernet connector is a separate connector on the radio. I try to scope the Ethernet but my Modis Ultra scope is too slow to get any waveform that will help me. I unplug the Ethernet connector at the radio and we do not lose audio. Okay cool at least I know now that if the telematics loses comm with radio the audio will still play. Just another clue that leads me to look at the radio because its responsible for audio output. At this point the car acts up for me, the screen goes black and the audio stops. I can still communicate with the Telematics module during this time, Sweet now we are getting closer! I load up the radio powers and grounds with a headlight bulb. They pass and terminal tension is good. Also remember that the radio is connected to multiple other networks on the car and no other module is reporting loss of comm with the radio. So the chance of there being a power or ground issue to the radio is slim. But I check them anyway. I decide to go on a test drive with the Ethernet connector disconnected at the radio and see if it still happens. The concern happens like 3 times on my 10 minute test drive, I held my phone up and was able to capture the concern coming and going in this short video


That was all the information I needed to condemn the radio. I ordered and installed and programmed a new radio a few days later. The new radio fixed the concern and was an updated part #. Hopefully this helps someone and even though vehicles increasingly more complex, a logical an systematic approach is still the best method while using the information and clues we have available. Please give any input on different tests that could have been performed and Ethernet operation. 

Marlin Technician
Marlin Default

You did very well, IMO. If you had not been able to duplicate it, the decision would have been much more difficult, I assume. Driver-provided symptom descriptions can be amazingly inaccurate.

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Steven Technician
Steven Default

Great article, thank you!

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Caleb Technician
Caleb Default

Thanks everyone, Yes I was pretty happy when it started happening!

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Randy Curriculum Developer
North Carolina
Randy Default

That shows a great diagnostic thought process. Super job!

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Brian Owner
Brian Default

Nice work, I have not had the thrill of this network, still getting my feet wet with the GM MOST network. We will need some faster scopes in the future.

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Andrew Technician
Andrew Default

I just had one the other day. I was able to diagnose it by the codes set and looking at the GDS2 and data bus tools. First clue is the U code set in the VCIM. I like to remember it as any “U” code set in a module is reporting a problem with YOU, meaning the module it talks to. In this case the radio. Watching the data freeze and reset on GDS2 and then watching it disappear off the data bus tool…

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