GMLAN Diagnostics

Martin Instructor Burnaby, British Columbia Posted   Latest   Edited  
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Network Communications
2019 Cadillac XT4 Luxury 2.0L (4 LSY) 9-spd (9T50)

While the DLC drawing in this post relates to a 2019 XT4, the real focus is data communication system changes since ~2017. GM vehicle data communication systems have begun to incorporate Serial Data Gateway Modules (aka Central Gateway Modules) for cyber security, as has been expressed elsewhere.

This may pose some new challenges in the diagnostic approach, not only for technicians who do not regularly utilize information retrieval systems, but also for those who may have learned to diagnose GMLAN systems for vehicle model years prior to 2017.

If you mastered the diagnostic routine easily enough for pre-2017 models, expect to do some reading about the updated electrical architecture, because you will need to revise your diagnostic approach.

Whether it is a 2017 Silverado, XT4 or other new model, be ready for some changes and added diagnostic time over what you may have experienced in the past, even on some vehicles built on the same platform.

Looking at the drawing, can you see the implications of attempting to follow the same old diagnostic practices on GM vehicles, whose data communication systems are now represented by the X84 DLC as shown?

I believe that it would be fair to predict that those who do not incorporate service information into diagnostics until they get stuck, could well be heading down a "rabbit hole" on the new breed.

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David Diagnostician
Philadelphia, Pennsylvania
David Default
 

Martin, is this similar to what the newer Mopars are doing? And should we be anticipating a MDI 3 because of this change?

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Hi David. My focus is GM only, so am not sure exactly what Mopar and others are doing for cyber security measures. We heard a rumour quite some time ago about the next gen scan tool interface, but that was all that it was a rumour. Of course, the reality is that just like vehicle design and planning, scan tool interfaces have to be in development early on, to accommodate the next wave of

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David Diagnostician
Philadelphia, Pennsylvania
David Default
 

As far as you know, is the MDI 2 100% backwards compatible with everything OBD2?

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

It Depends®. There are some GM vehicles with which MDI 1 and MDI 2 do not function well completely. The MDI was designed for use with Global "A" GM vehicles as both the GM approved J2534 programming device and scan tool interface through the original short-lived GDS scan software and the next generation GDS 2. sandyblogs​.​com/techlink/?p=64… The Tech 2 was still able to function

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