Hey all, I recently (April) picked up a 2004 'burban at auction. It was a bit rough, but ran and was worth putting money into. Only 193k on the odometer. I have also never owned a Chevy, but I am quickly becoming a fan because of all the work I can do myself.

There have never been any electrical or control module issues until recently. The ABS light (ABSLT), Parking Brake light (PBLT), and Traction Control light (TCLT) all come on at the same time. This started a few months ago. They all go off together, too. So far, they never come on independently. When this happens, the Climate Control and Cruise Control are not functional in any sense. The Climate Controls seem to default to the foot zone (even if the indicator is on vent), and only hot air comes out. Note, I have already replaced the diverter door on the lower passenger side. Even though it's on the passenger side (you all probably already know this) but it controls the driver's side controls. Anyway, it was replaced and is working fine. I have also tried to reset the Climate Control system by pulling the 10A fuse and letting the system perform a self diagnostic and reset. If the ABSLT, PBLT, and TCLT are already out, this will work and the Climate Controls will go through a self-test. If the lights are on, it won't have any effect.

The ABSLT, PBLT, and TCLT all come on and go out together. Sometimes, they will stay on for days or weeks, and just go out for no reason. Then the A/C and Cruise work fine. As soon as they come back on, theClimate Control and Cruise are non-functional again. When the lights all come on together, I have tried to use my MaxCOM scan tool to read the DTCs from the module. No luck. I get a communication error. I have also tried to communicate with the Cruise Control module, and the Climate Control module. Same result. Failed to communicate.

I can't figure out why the Cruise would be affected by the EPBCM, if that's actually the problem. I also can't figure out why/how the EPBCM could affect the Climate Control. If I can't figure things out myself, I take my 'burban to Christian Brothers Automotive (CBAC). I'm not promoting them. Just giving some flavor to the story. I'm NOT taking it to a Chevy dealer, because if the EPBCM is bad, this part is discontinued anyway and Chevy doesn't have one. So CBAC ordered an aftermarket part from Dorman, and they told me that it's a 50/50 shot whether they work the first time or not. They put one in today and got the same response, "Failed to communicate." They are going to order another and try again.

They said that there are three possible grounds that could also be the issue. They checked two of the three grounds, and there was no issue - no corrosion, good contact, etc. The first two grounds are under the dash on the driver's side or in the engine bay. The third is in the back, in the cargo area on the passenger side, by the rear lift gate trim. We didn't bother checking the third because this is a Texas vehicle. Also, because I have been able to either bump the steering column, or the dash, and get the lights to go out temporarily (30 seconds to a minute). So it seems like it's either a faulty contact inside the EPBCM, or a loose wire somewhere. But we can't find any loose connections. They checked all the connectors, and they seem good.

The Service Manager at CBAC speculated that maybe there's something going on in the CAN BUS system and when the ABSLT, PBLT, and TCLT come on it's somehow knocking out communications for the Climate Controls and Cruise. But, he also said that the last two run on the lower range, and the ABSLT, PBLT, and TCLT all run on the upper range. I don't know much about how a CAN BUS system works, but I know what it is. So I don't understand how this can happen, but I'm no GM Engineer either.

I am an Engineer, but that just makes me ask more questions with the same level of ignorance about the problem.

SO... I'm hoping that someone out there has some experience or information that they can share on how to troubleshoot this, and perhaps why I'm seeing the symptoms that I am.

Much appreciate. Thank you in advance.

 

It appears that I can't edit my posts, so I'll just add my comments here.

I was doing some research last night on the EPBCM. As it turns out, it appears to be a mostly mechanical component that is integral to the Parking Brake. I assumed (incorrectly) that it was like all the other modules I have seen in the past; a flat metal box, grayish or silver in color with heat dissipating ribs as part of the casing, and mounted under the dash, console, or under the seat(s).

This is definitely not the problem:
Emergency Parking Brake Control Module

So, I got thinking about how these symptoms could all come together. The issues must be in the Body Control Module (BCM) which is located under the steering column. I had assumed that this was the EPBCM.

Anyone have any thoughts or comments?

This is a MUCH cheaper option, if it's really the problem.

 

Yeah, it's not the BCM either, because that just doesn't make sense. I found the description of what the BCM regulates, and there's no overlap, other than the fact that the Climate Controls cut out when the ABSLT, PBLT, and TCLT comes on. I'm still at a loss.

 

Anyone?

 

This is old tech so l'm not sure if the architecture for the computer system. To old for can bus???.
Find a schematic for the computer network.

If it's wired in a daisy chain see if all the offline modules are in series.
Causes of loss of communication can be from :
-no power and grd to each module
-open, shorted communication wires
-bad modules
Start by checking for power and grd to each module
If that is good, check each comm wire for continuity, short to power, short to grd or shorted together.
If those are good ....replace module.
If you look up the system and it uses a can bus...diag is different.