SOLVED - Big 3 upgrade, EVERY warning light on immediately after.

[Tyrant]

Update:

4WD (4 high/auto/2 high, NO low) still works, ABS/traction control are completely non functional, and it randomly goes into limp mode on start-up.

There's no rhyme or reason to it... It'll refuse to downshift, won't rev past ~2,000 in Drive (but will in lower gears), and it's gutless. If it wasn't supercharged, it probably wouldn't even be drivable.

I can park, shut her down, and fire her up with no limp mode. Sometimes it'll take 2-3 restarts, sometimes it'll stay for the entire day.

It happens when it's 80° out, 30°, and everywhere in between.

I found a guide that suggested measuring resistance at the diagnostic port a while back, but misplaced the link before I could get to it. I snagged a new multimeter, as my old one finally bought the farm. Do you guys have any info on which pins I'd need to test and how much resistance I should be looking for?

Thank you again!

 

[HACK BLOCK]

might be worth it to take it to a professional now

 

[Tyrant]

Unfortunately I'm beginning to think the same. I'll give it one more whirl by trying to test the modules, I hate paying "diagnostic" fees that are easily inflated.

 

[CaptainAmerica1]

Seems you’re in over your head. Take it to a professional. I know what they’re gonna find. But you do you homie….

 

[Tyrant]

Update:

Went to a local shop, worked with the techs there for a few hours to try and narrow it down.

They are convinced that the ABS module is the root cause of the issue. Voltage and resistance measured at the ABS plug is as it should be.

After I got home, I measured resistance between pin 6 and 14 of the DLC and what did I find - 120 ohms.

The rear terminating resistor reads 120, so that's a no go. From what I'm reading, the other resistor is actually in the ECU.

 

[CaptainAmerica1]

Keep ignoring the obvious. I’m sure you’ll burn it to the ground in no time…

 

[George B]

Did you and the shop confirm a handshake from each of the modules with a scan tool? How did they come to the conclusion it’s the ABS module?

I am still of the opinion some module is fried unintentionally.

 

[petethepug]

Reliable Automotive Electronics Rebuilder | ARES Technologies

An automotive electronics rebuilding leader, ARES Technologies delivers high-quality ECM, PCM, TCM, and FICM modules for vehicles. Shop online!

arestechnologies.com

$129 for a new BCM coded to the truck.

 

[Tyrant]

Did you and the shop confirm a handshake from each of the modules with a scan tool? How did they come to the conclusion it’s the ABS module?

I am still of the opinion some module is fried unintentionally.

The measured resistance at the DLC tells me you're probably right. The shop tech I worked with's explanation for the ABS module suspicion was basically that it interprets the readings from the hall/wheel speed sensors at each wheel, then sends the data to the other modules.

That would explain the absolute disappearance of the ABS module in the Tech 2 and the Snapon readers, as well as the traction control.

It doesn't explain the TCCM and FPCM codes, to which I think your suggestion is more appropriately linked.

Thank you!

 

[Tyrant]

Keep ignoring the obvious. I’m sure you’ll burn it to the ground in no time…

Alright, I'll humor you since you're so insistent - ripping out 0 awg wire and replacing it with stiff, pre-moulded 4 awg will magically fix the canbus? Are you volunteering to pay Stealership prices for the wire and then reimburse me for the time when the obvious occurs?

Nothing is disconnected. I've gone over every single connector in the vehicle, including those behind the dash, blown them out w/ compressed air, and slathered them with dielectric grease.

I've replaced every J case and mini blade fuse. I bought Tech2Win and ran through the diagnostic protocol with that, followed the TSB for these issues, and then doubled down on the diagnostic with somebody more acquainted with GM electrical than myself.

I'll appreciate any constructive criticism, but I don't personally care if you have a vendetta against "Big 3 upgrades", so I'm directly asking you to keep the glaring negativity to yourself. I don't have a tantrum when people stuff 22" chrome wheels on their SUVs or lower them, even if it isn't my cup of tea. I addressed constant headlight dimming and very rough starts in -20° weather by choosing to decrease the resistance between my battery and the starter/distribution block. On the plus side, it worked - on the down side, I inadvertently stumbled upon something else in the process. Whether or not I caused a short inadvertently or simply unmasked an existing issue doesn't change the fact that I'm trying to address it now.

I appreciate your earlier, more constructive input and I'm not saying "Boo, go away" - I'm only asserting that I don't care for the constant sarcasm and negativity. I'll welcome any reasonable attempt to help, as I hope people can tell from my interactions thus far.

 

[Tyrant]

Reliable Automotive Electronics Rebuilder | ARES Technologies

An automotive electronics rebuilding leader, ARES Technologies delivers high-quality ECM, PCM, TCM, and FICM modules for vehicles. Shop online!

arestechnologies.com

$129 for a new BCM coded to the truck.

I think that's the most logical course, at this point... The other terminating resistor is built into the BCM for these guys, isn't it?

 

[Speck]

Any updates? My hat's off to you in your persistence in continuing to troubleshoot. I am hoping that you have resolved the issue and have just been too busy enjoying your vehicle as it should be to be posting on here.

 

[Tyrant]

Thank you for your kind words, Speck!
Unfortunately, no solution thus far.

I'm still driving it every day, although I've been more and more annoyed with this issue as a result.
I pulled the underhood UBEC, blew it out with compressed air, sprayed it thoroughly with contact cleaner and let it sit until it thoroughly dried. I inspected each and every connection, checked every fuse for continuity, and re-seated them for a second time just to be thorough.

I still see ~120 ohms at the DLC, although I've ruled out the rear terminating resistor already. I have yet to try a different ECM (next on my list), however I did replace the BCM with a programmed unit to no avail - I was able to return it, so that was fortunate.

I went against my better judgement and threw OEM power and ground wires back on for a day - apart from annoying me and eating up more time, that was also a bust.

The entire high-speed channel is out, so the termination is the most likely cause in my opinion... The only thing that truly ISN'T functioning is the ABS itself. That wouldn't explain the other modules presenting U codes, however... I wish that it were feasible to simply tear the ECM apart and replace the resistor, that appeals way more to me than throwing $3-400 darts at a board...

 

[Tyrant]

I'm too stubborn to call it quits, so I'll figure it out eventually. I just may be in for a rough winter in the meantime!

 

[B-train]

Have you tried disconnecting the ABS unit to take it out of the loop and see what happens? Maybe try pulling the fuses first.

You could also try removing all power again. Power down your dash cam or whatever is hardwired in. Touch the positive and negative cables together and hold for a few seconds. This will drain the capacitors in the computers. Honking the horn with the battery disconnected can do the same thing too.

Power back up with positive cable landed first, negative last. Turn on the key without starting and just let stuff wake up. Not sure if this will help, but sometimes a hard power cycle can be beneficial.

 

[Tyrant]

I have; unfortunately, each individual module (I tried all of them, individually and together) yielded no effect.
I definitely appreciate the suggestions, nothing is too silly to try at this point.

I think I'm at the "buy an ECM and hope it works" point, considering the consistent ~120 ohms at the DLC. Improper termination is the only thing that makes sense to me, given the parallel nature of these systems...

 

[Tyrant]

I just thought of something... does GM use the ABS module as a gateway for the other modules? If so, that might explain a failure to communicate, despite the parallel nature of their functionality. If the CANBUS itself isn't parallel, but the power to each module is, that could potentially explain them failing to communicate but functioning otherwise - at least that's what I'm wondering now.

 

[mattbta]

Pine Hollow Auto Diagnostics channel on YouTube has a pretty cool series on an Avalanche with bad class ii network and his troubleshooting steps. Think it has “parts cannon” in the title. Works his way through all the modules with a pico and test lights. Might give you some insight on the various systems and relations. Good luck.

Edit: it was a Suburban. Here’s part 1:

 

[Tyrant]

I'll give it a whirl, thank you!
The part that drives me the craziest here is that it runs and drives, w/ functional 4WD... yet ALL hi-speed canbus modules fail to communicate.
If it was a lawn ornament, I'd have probably figured it out by now

 

[Fless]

Pine Hollow Auto Diagnostics channel on YouTube has a pretty cool series on an Avalanche with bad class ii network and his troubleshooting steps. Think it has “parts cannon” in the title. Works his way through all the modules with a pico and test lights. Might give you some insight on the various systems and relations. Good luck.

Edit: it was a Suburban. Here’s part 1:

It may have been the Esky you were thinking of: