Removing modules from data bus

[Elizabetty]

If a bad module can potentially take down the data bus, and the module isn't necessary to me, can it be removed? For example, I have no need for the four-wheel drive when I have bigger fish to fry right now. If I simply unplug the tccm, a scan will of course show the u1000 error, for example, from no communication with the tccm. However, if it's left plugged in, it seems to affect the ability to communicate with other modules.

Is there a way to take it off the network or is it something the PCM will always be looking for? I'm not sure if removing it from the splice pack would be part of that or if that's even an option. I've read about unplugging the comb and jumping the pins etc to find the problem module, but let's say it turned out to be the tccm and there was no interest in replacing it if the vehicle was left in 2hi. Would simply unplugging it and letting it give the data bus error code be the way to go or is there a way for it to be temporarily taken out of the picture?

Additionally, if my radio itself is shorted out, and not the wiring, unplugging that gives the loss of communication code with radio also. My question applies to this scenario as well.

I'm not clear on what is affected with a bad module knowing it can take down the data bus communication. If it's unplugged is that the same as having it plugged in with it being faulty? I guess that's why I was asking about removing it completely from the situation.

 

[mrrsm]

Yes... And as a Basic Experiment... If you have diagnosed a Shorted or Failing Module as per Will Robinson's Superb GM Class 2 Network Diagnostic Video.... Just Unplug it... AND also Remove its Fuse; either from the Front or from the Rear Fuse Block as well and see how the Class 2 Network Behaves. Make certain to Check out the B-Negative Ground Connection for the BCM Fuse Block under the Rear Driver's Side Seat ...right at the adjacent Body Pillar, too. :>)

This is another On Topic Viewing regarding Intermittent Class 2 Network FUBARs and finding these of a more contemporary nature can be helpful to us ALL by remembering that THERE ARE TWO CLASS 2 NETWORK SPLICE PACKS IN THE GMT360 SUVS and that conducting any Class 2 Network Diagnostics is VERY straightforward when using a 16 Pin DLC Break-Out Box along with an Inexpensive Hantek Model #1008C Oscilloscope Kit:

That Last Video Poster ( The Pro Auto Repair Dude) asked for Viewer Feedback and Criticism... Here is MINE:

Hey NEO.... Wanna be a Better Automotive Diagnostician and justify spending $12,000.00 for your Snap-On ZEUS Scan Tool-Lab Scope Combo...?



DON'T FOLLOW THE WHITE RABBIT...!!!


Instead... Visit Amazon and Buy THIS Inexpensive Hantek Model #1008C Oscilloscope Kit and THEN Use Your Common Sense, Don't Overlook The Obvious and Follow Proven, (Plodding) Diagnostic Steps to properly Figure Things Out!

Hantek 1008C 8CH Automotive Diagnostic Oscilloscope: Amazon.com: Industrial & Scientific

Hantek 1008C 8CH Automotive Diagnostic Oscilloscope: Amazon.com: Industrial & Scientific

www.amazon.com

Images Credit: "The Matrix" by YouTube Screen Caps via YouTube

 

[Mooseman]

And it also depends on which module. Some are essential, like the PCM and BCM, while most of the others are semi-essential.

Why do you think the TCCM is causing an issue? That one you can leave it unplugged and all you'll get is a service 4x4 light. Although we've had issues with some other modules (DDM, PDM, rear entertainment), the TCCM can fail however haven't seen or heard of one causing issues on the CANBUS.

 

[TJBaker57]

Personally, from having learned to read, decode and understand the messages on the serial data bus and thus I have seen with my own eyes the chit-chat between the various modules I would not remove modules willy-nilly from my vehicle serial data bus except during the course of troubleshooting.

If you are seeing a permanent loss of communications code set, NOT a pending, old, history, etc..code then this is worth tracking down and resolving.

If it is not a recurring current code it is not worth spending a great deal of time chasing.

Further, a loss of communications code does NOT automatically say it is a problem with the data bus. A module could have a power or ground issue that intermittently takes it offline and this too results in precisely the same loss of communications DTC.

On nearly a daily basis I see examples of this sort of diagnostic issue that can be investigated logically for a few $$ and I am reminded of the old Geico commercial slogan, "15 minutes can save you 15% on your car insurance". And here $15 and 15 minutes and I can show you how to see the serial data traffic yourself.

https://www.amazon.com/gp/product/B011NSX27A/?tag=gmtnation-20

 

[mrrsm]

Thomas... You would be the extraordinary exception to "The Rule". Most people feel like this:

"I Use a Watch to Tell the Time. But I Don't Know How it Works and I Don't Have the Time to Learn..."

Which is generally the mental state of most people in trouble with Disabled Vehicles that need to "Run and Get to my Job Site..." or to "Have to take my Kids to School..." . They will also want to consciously avoid making any Expensive Stop-Overs at their Local Chevrolet Dealerships and have their Pockets Picked Clean.These Folks are often fearful of doing more harm then good by attempting their own repairs;.even when counseled with the best of intentions and advice possible.

You and I and few others like us here have emerged from a Post 1950s North American Era where knowing General Automotive Mechanics was an expected "Right Of Passage" that has allowed us to make such appearances at the Local Dealerships be matters of choice rather than necessity. Hell...most of the time...We SCOFF at Them!

But then came OBD I in the 1980s followed soon after by ODB II in the 1990s and so forth. On and on these engineering developments followed right along with their often complex Mechanical Failures like a steady Trail of Tears for the many people with SUVs and Trucks breaking downs and having only the Internet as their final port of call for assistance.

For us, never knowing their levels of Mechanical Understanding and Ability (or Disability) with using Detailed Procedures or Expensive Tools to solve their problems can makes things worse, even after being provided with the Absolute Ground Truth about their Vehicles. Mix those problems with the endless need to improve our own understanding of up-to-date Automotive Systems and their requirements of needing complicated Diagnostic Tools and that all adds to the great mystery of how best to advise and coach Folks through the maize of these difficulties.

 

[Elizabetty]

I'm not certain the tccm is 100% bad. It was a coincidental thing that made me post the question to understand the system a bit better of what happens when a module is disconnected and how that may temporarily solve a problem. I just happened to be taking my dash out to do some further wire investigation behind the HVAC module and noticed the wires to the tccm were pretty warm and so was the module but as soon as you moved about an inch and a half away from the module up the wires, there was no more heat. It led me to think my learning and testing may result in a bad module and if so, how do you go about having a functioning communication system with a module that isn't connected.

I plan on getting the item from Amazon that TJ mentioned. Right now I've been focused on learning the differences between an open circuit versus a short to ground and a short to power. I'm not sure what I will find. I have to do everything in tiny stretches because I keep getting minor frostbite cases on my hands and then I lose feeling for the rest of the day LOL I don't get very far doing a little bit at a time but they say curiosity killed the cat and here I am being curious about how you remove things if necessary to understand how the communication system can still work if they're all essentially working together.

I assure you I am slow but steady with the resources supplied. My brain is one of those that can't help but wonder about the next piece of the puzzle before I even get there sometimes.

 

[Elizabetty]

I've seen the fancy tool that has all the separate leads to basically add the modules back in when the comb is removed. I've seen people do this with a jumper wire too. Just as effective or with limitations?

 

[mrrsm]

You can use a Large & Small Pair of Baby Diaper Safety Pins:

... and accomplish the very same thing. The AES Wave Hollow Pin Harness Kit for this Job is ridiculously over-priced but it will do the same job just as well. Just follow Will Robinson's use of the Two Safety Pins to get the right idea of how to DO this Job:

 

[TJBaker57]

I simply take a bundle of small wire sections and strip the ends then use a wire nut to secure one end of all the wires together. Here is one such without the wirenut on it at the moment.



As I have stated before, I'm cheap!!

I now have the free ends to use to insert into the splice pack one at a time as needed to add modules in.

And instead of a high priced scantool or oscilloscope I just put my $15 OBD2 adapter into bus-monitoring mode which simply prints every message on the bus to the phone screen so I can see if traffic is moving OK or not. If I connect a module and all the messages stop I know I have located an issue!

 

[Elizabetty]

I simply take a bundle of small wire sections and strip the ends then use a wire nut to secure one end of all the wires together. Here is one such without the wirenut on it at the moment.

View attachment 107247

As I have stated before, I'm cheap!!

I now have the free ends to use to insert into the splice pack one at a time as needed to add modules in.

And instead of a high priced scantool or oscilloscope I just put my $15 OBD2 adapter into bus-monitoring mode which simply prints every message on the bus to the phone screen so I can see if traffic is moving OK or not. If I connect a module and all the messages stop I know I have located an issue!

Love this. I was kind of hoping something like this would show up in the responses because that's what I picture in my DIY brain. Are you using 18 gauge wire?

 

[TJBaker57]

Love this. I was kind of hoping something like this would show up in the responses because that's what I picture in my DIY brain. Are you using 18 gauge wire?

Pictured there is 22ga. I have also used 20ga. I always use solid wire for this. More frequently I use a longer strand than the one pictured as well.

The twisted ends should be covered up either by a wirenut or electrical tape or even heat shrink tube.

20ga is the closest I have found to the thickness of say a fuse or relay tang that inserts to a fuseblock or the like. This 20ga thickness as measured with an inexpensive low resolution caliper is 0.7mm or 0.03 inches.

 

[Elizabetty]

Pictured there is 22ga. I have also used 20ga. I always use solid wire for this. More frequently I use a longer strand than the one pictured as well.

The twisted ends should be covered up either by a wirenut or electrical tape or even heat shrink tube.

20ga is the closest I have found to the thickness of say a fuse or relay tang that inserts to a fuseblock or the like. This 20ga thickness as measured with an inexpensive low resolution caliper is 0.7mm or 0.03 inches.

Glad I asked. Ty!