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2003 gmc envoy_slt_xl
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Discussion Starter · #1 · (Edited)
Alright, I have been trying to work on my wife's 2003 Envoy XL ABS problem for a while. I've read all the posts I can (there are a lot) on ABS issues, but I've progressed to a point where I need some advice. Let me tell you the symptoms and what I've tried.

The problem is basically the ABS and Brake warning lights coming on at the same time, chirping, and then the driver info system displaying "SERVICE BRAKE SYSTEM". The brake system seems to be working fine by itself, but I'm sure I don't have ABS brakes. At first, it came on every 2-3 days, but now it comes on virtually every time the truck is driven. It comes on independent of use of the brakes. In fact, it will often come on shortly after ignition on without ever having touched the brakes. But, every now and then we can drive 10-20 miles without it coming on.

I've tried what appear to be the traditional remedies. I've reworked the ground wire beneath the driver door (on the outside of the frame). I exposed metal using a Dremel. I even soldered the crimp to make sure the connection was good. I did the same thing to the battery ground wire that attaches to the left fender inner wall.

There was some discussion about the ignition switch causing some problems. Although that one didn't seem to fit, I was able to get it fairly cheaply so I replaced that.

I checked the FRONT wheel speed sensors. I actually bought some from Partstrain with the intent of replacing them, but they sent the wrong part. So I checked both with an AC voltmeter on the connector while spinning the wheel with my finger and was able to get ample voltage. I also inspected one of them visually, and it appeared to be in fairly clean shape. (I would have inspected the other one, but while spinning the wheel my finger got caught between the spoke and caliper. That ended my investigation for that evening.) I did NOT check the rear wheel speed sensor. But since the lights come on even before the wheels start spinning, makes me think wheel sensors are unlikely as the source of the problem.

None of the above remedies helped at all. I eventually got ahold of the CP9449 scan tool, since my regular scan tool doesn't support ABS. And lo and behold, four scan codes emerged. They are:

C0298 PCM Fault
C0265 EBCM Motor Relay Circuit
C0245 EBCM Control Valve Circuit
C0241 EBCM Control Valve Circuit

Now I would have to believe that some of these code faults are "domino" faults, wherein a fault is occurring only because some other device has failed. So I would like to try fixing this in some logical progression. But what would need to be replaced? And in what order?

And perhaps I need to ask an even more basic question. I have a feeling that I might end up having to replace the entire EBCM assembly. And I have the impression that this requires special tools, programming, and the like, and would have to be done either by a dealer or a very well equipped mechanic. I am neither. So is this a repair that I'm even capable of performing?

I have no experience with ABS repair, but am mechanically inclined and do a lot of my own work on my vehicles, generally learning as I go. But if this requires tools or procedures I don't have, I might have to give this one to the dealer. What do you guys figure if I do? $800? $1200?

Any opinion is welcomed.

Thanks.
 

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2003 gmc envoy_slt
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:tiphat Welcome :tiphat . When you can , fill out your User CP info. That way we don't have to look through your post to see what your driving and if your area may have an influence on your problem. This may not help but, every time I see a PCM fault I think of disconnecting the battery for about 20 minutes to reset the PCM. As stated, it may not help, but it takes it out of the equation. And it's free. Also, how many miles since the brakes have been bled? I don't know if old nasty brake fluid will cause codes to be set. Hopefully someone will join in soon. Good luck.
 

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2004 chevy trailblazer_lt
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Look underneath the truck, on the driver side frame and follow it forward to just past the drivers door. There is a stub crossmember, and bolted to it is the ground for the EBCM. It is easy to find; it is a ring end on a thick wire with a tiny tab that fits into a slot. Remove the bolt, polish the ring end, polish the frame where the ring makes contact with it and make sure you are getting good ground. Bolt it back up and touch up the bare metal with a shot of rubber undercoating spray.

This may or may not be the problem. If there is a bad ground here, it usually manifests itself in a "loss of communication to the EBCM" code, but it is an easy fix and costs nothing to try.
 

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Discussion Starter · #4 · (Edited)
Look underneath the truck, on the driver side frame and follow it forward to just past the drivers door. There is a stub crossmember, and bolted to it is the ground for the EBCM. It is easy to find; it is a ring end on a thick wire with a tiny tab that fits into a slot. Remove the bolt, polish the ring end, polish the frame where the ring makes contact with it and make sure you are getting good ground. Bolt it back up and touch up the bare metal with a shot of rubber undercoating spray.

This may or may not be the problem. If there is a bad ground here, it usually manifests itself in a "loss of communication to the EBCM" code, but it is an easy fix and costs nothing to try.
I'd like to follow up on this one, because I DID 'repair' a ground connection of a ring lug of about a 12 gauge black wire with a tab that fits into a slot on the frame, and is bolted to the frame. However, this ground connection was even with the driver door hinge, on a cross member that sits on the outside of the frame (what looks to be a shock mount). The bolt itself actually faces to the rear of the vehicle.

This is the repair I described in the OP, (perhaps not clearly). But I was never 100% sure from prior posts exactly where the ground connection was supposed to be found. From reading your comment, I think I did repair the right one.

This had no effect.

I did remove battery power for 30 minutes just now. I'll let you know if that has an effect.

About bleeding the brakes...

I didn't mention this before, but when the "brake failure lights" first occurred, my wife was far, far from home, and I had actually just removed the front struts off my car, so I had no way to help her. Without knowing the seriousness of the issue, I told her to seek the nearest garage. The Firestone place replaced her pads, (which bugged me since I had new pads in the garage ready to be installed) and they bled the brakes. that was a couple of months ago. The problem reappeared about 3-4 days after that. But back then, the problem occurred much more rarely. So my opinion is, that Firestone didn't address the problem at all. I've thought about bleeding the brakes on my own, just to make sure they didn't leave in a air bubble - but I don't think that's it either. After all, the lights will come on even before the brake pedal is touched.

Thanks, btw, for your quick replies. Keep 'em comin'.
 

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2004 chevy trailblazer_lt
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You found the EBCM ground I was talking about.

Too bad, because that is the easy fix.

Basically, you are now down to four things:
- ignition switch (which you have done)
- loose or corroded battery cables
- loose connection to the EBCM
- internal failure of the EBCM.

All signs point to #4.

Sorry but that's the extent of my limited advice. I think the EBCM replacement is a dealer-job because there are a LOT of parameters that must now be reprogrammed into it using a Tech II tool. (Tire diameters, etc.)

Good luck and let us know. Sadly for you (but thankfully for everyone else,) it appears this is a rare failure.
 

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Discussion Starter · #6 ·
UPDATE: I will continue to update this as things are tried, succeed, or fail. If nothing else, this can be info for the next guy.

The attempt to reset the PCM by disconnecting the battery for 30 minutes had no effect. I also, just to be sure, measured the impedance between the EBCM ground on the undercarriage and the battery, and measured 0.2 Ohms. That seems like such a likely cause, I'd still like it to be it. But it isn't.

(BTW, just as the EBCM ground must be good on the frame beneath the driver's door, there is a separate ground wire from the battery post to the left side of the fender wall. That must be good too. But mine checked out okay.)

I may just have to take it into the dealer. But right now, I'm looking at a guy on ebay that refurbishes the EBCM if you send it in. Wow, I'm pretty skeptical, but is this possible?

ebay item
 

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I know this post is almost a year old, but mine has been doing the same thing for months. I finally got a EBCM scanner on it yesterday and there were about 12 codes. Way too many, so I cleared it and the first one fired this morning before I got out of the driveway - CO265. I've reseated the the ground under the driver side door, but not the one under the hood yet. I seem to remember this getting worse after having my brakes done at a Firestone as well. Coincidence?? Is this just an annoying MIL that I continue to live with? Or will my brakes randomly go out when I'm coming up on a family of ducks crossing the street? Any updates on this ghost in the machine? :confused:
 

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Discussion Starter · #9 ·
As coincidence would have it, I finally decided to drop it off at the local GMC dealer just this past Saturday. We were operating with the ABS disabled for all this time. The vehicle seemed to brake like a typical 'non-ABS' system would brake. Once, I even had to avoid a highway crash in front of me at 70 mph, and the vehicle handled fine through the braking.

For the record, I did pull the 30A fuse for the ABS system many months ago. I figured if the ABS wasn't active, I might as well kill the power to it just in case the failure mode was progressive or would cause additional failures down the line.

I plugged the fuse back in last week, and the ABS lights still chimed, and the ABS code reader still gave me the same four codes it did before. So we took the vehicle in. I felt like it was likely that the PCM Fault meant that the EBCM was bad, and I'd just have to have it replaced.

Well, that was the original diagnosis from the dealer, that they had to replace the EBCM at a cost of $654 for parts and labor. Not too bad. The thought is that the other codes are a result of the failed EBCM. But the part is on order and the work still needs to be done. I'll be happy when they say that everything is working with that one part replaced. I'll post when I get the final word.

BTW- The dealer offered us a free loaner while we wait for the part. It's a Buick LaCrosse CXS fully optioned up with the nav, premium sound, XM, rear camera, etc - with only 800 miles on it. Not a bad ride for a loaner. When did dealers start giving these things out? The last time I got a loaner they gave me a Chevy Aveo.
 

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2004 gmc
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When did dealers start giving these things out?
Perhaps when they figured that loaners are marketing tools, and when one's original vehicle is in the shop for a multi-day potentially expensive repair is when the mark .... I mean esteemed customer .... is at their most vulnerable to a sales pitch. I'm certain the service manager tells his buddies in sales when a repair estimate goes north of $1000 or 2000. :dielaugh:
 

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2005 gmc envoy_denali
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Help with ABS code C0265

Would like to know if there have been any follow up to the issue mentioned by Swindler above. Our vehicle is displaying the exact same thing and appears to be common to what is described above. I too, have cleaned the ground wiring on frame and resealed it to keep out moisture, but that provided absolutely no fix to the ABS Service Brake warning that comes on every time that the vehicle is driven over about 4 miles. My next attempt will be to remove the ABS module and look for cracks/bad solder joints on the circuit board. I know that it can be repaired by sending it out to a vendor, but seems to me if they can do it, then I probably can also. :undecided Any additional info is welcome.
 

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Discussion Starter · #12 · (Edited)
Sorry I never properly closed out this thread as the problem was solved, and sorry I didn't reply to you 'rdy2ride'. I've been out of the car repair business for a while now, as I developed a medical condition and haven't been keeping up with my vehicles. The Envoy (which I still have) and my other car were in the driveway for almost two years without being driven. I would have my son charge the batteries occasionally, and once in a blue moon run the engine, but little else. I haven't even driven a vehicle in all that time other than moving cars around in the driveway. *sigh*

BTW, when we did finally get to a point where we needed to resurrect and drive the Envoy, we found that squirrels had been living under the hood and there were dozens and dozens of acorns not only under the hood, but somehow found their way into the cavity above the AC blower motor. There was a HUGE stash in there. The AC sounded like a blender when you cranked it on high. I had bought a new motor, but all it needed was to be de-acorned. If that wasn't bad enough, the squirrels apparently ate through the power steering hoses and we had a bad leak there. The mechanic said he never saw that hose so 'chewed up'.

As far as the ABS, the repair we had the GMC dealer perform fixed everything. We have since had no lights, codes, or anything else show up with respect to brakes. I have had to fix a couple of other things, but nothing related to the ABS.

Incidentally, my new issue appears to be the infamous cracked exhaust manifold, but am still not sure I'm strong enough to do the repair myself. The Dorman part isn't too expensive, so I'd like to just try swapping the part if it's not too hard to access. I might try to get it done when my son is home for the weekend. He's actually more adventurous than I am when it comes to working on cars.
 
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