Replace rubber brake lines, yea or nay?

[02FailBlazer]

C0267 is pretty definitive if it's been diagnosed properly to rule out a wiring or power issue to the module. If the valve is stuck open, I could see that causing the issues.

Hmm. I'll take a close look at any connectors/wiring/grounds I can access before buying anything. Guess I'll pull and inspect the ABS fuse too.

Just seems weird that this pops up after changing some brake parts. Maybe the first fluid flush was enough to cause something already on the verge of failure to give up? Dunno.

Should also mention I've never gotten an ABS light.

 

[02FailBlazer]

Turning this over in my head some more and I'm wondering if it's actually the pump that's bad.

I was wondering why this issue would suddenly present after replacing those brake parts, seemingly out of the blue. Here's the thing - I absolutely neglected the brake fluid on this. When I went to swap the master cylinder, I saw that my old one was full of black gunk that caked the inside of the reservoir. Probably seals somewhere breaking down.

Anyway, I'm thinking that maybe when I did the fluid flush it pushed a bunch of gunk that was sitting in the lines into the pump/valves which played havoc with it. I'm not at all certain of this, and I have only the faintest grasp of ABS system design and operation, but it's something to consider.

Which leads me to my next point - I still don't quite get how even a stuck open valve would cause such a soft pedal and poor brake response. You'd think you'd still be able to max out the hydraulic pressure and lock the brakes up, just maybe with a bit more pedal travel? Don't know, but the valve explanation isn't making sense to me just yet. Not saying it's wrong, just can't wrap my head around it.

Like ok, maybe the fluid bypasses the valve when it shouldn't, but so what? It's a closed system, it can't go anywhere, right? It's not like this opened up a giant, empty cavity for it to flow into, and even if it did that would imply the presence of air in the system as the cavity would have otherwise filled with fluid by now. And if said cavity is filled with fluid, then hydraulic pressure should have been restored and the system would just act like a car without ABS? I know I'm missing something but this just isn't making sense.

 

[Mooseman]

Turning this over in my head some more and I'm wondering if it's actually the pump that's bad.

Yep since the code specifically says that the pump motor circuit is open. Again, barring any wiring or power issues to it (fuse/ground), the module is trying to power the pump and getting nothing.

It's quite possible junk got to the motor and when it tried to activate, it burned out because it was stuck.

If your pedal is firm enough (02-05 had soft-ish pedals due to the aluminum front calipers), then sure you can drive it without ABS. But if air got into it and the pedal is soft, then you will have to replace it.

 

[budwich]

I don't know anything about the abs operation but it seems rather "simple" in terms of "outward" electronics. The first concern would be the lack of indicator light on the dash for the fault code. Do you see the abs light during the "all lights" check with key on? As mentioned, have you checked the the voltage and ground conditions going into ebcm? It does not sound good for the ebcm module, if its not setting the indicator light?

 

[movietvet]

Brake fluid flush is one of the most overlooked maintenance services. It is important, in an instance like this, especially if you live in a mountainous area.

 

[02FailBlazer]

I'll still check everything I can to try ruling out the EBCM, but I'm very suspicious about the condition of the pump. Just doesn't make sense to me that an electrical fault like this would pop up out of nowhere and coincidentally right after a fluid flush.

And of course the pump is the one mechanical part on this thing you can't buy new or remanufactured. Guess I'll pull it off and see how serviceable it is, but I won't get my hopes up.

No can do on driving without ABS, my pedal is still soft as a kitten and the vehicle has maybe half the brake force it should have. FWIW, my mechanic triggered the ABS with his scanner and said he could hear the pump running. If the fault is somewhere inside the pump assembly, I'm thinking the motor is fine and there's gunk jamming up valves or other little passages inside it.

 

[budwich]

Can

Should also mention I've never gotten an ABS light.

does the light work? Based on what the garage guys did commanding the motor to run, it would appear to point at the EBCM module as having an issue and not fully operating valves. Check the voltage going in on the c2 connector along with the grounds. Specifically, disconnect the positive and negative as the battery. Disconnect the c2 connector at the ebcm. Do a resistance measurement at the positive disconnected cable to the battery pin on the c2 connector. Likewise for ground pin. Both should read very very low (ensure that you understand what your meter "zero calibration" is for the resistance function).

Having said this, if you have never seen an ABS light before this and thus never pulled codes, how would you know that the system is "in trouble". Was the ABS recently "firing" during some brake sequence?

ADDED: NOTE to check the powering connection (from positive battery to pin in the ECBM connector), the key must be set to "RUN".

 

[02FailBlazer]

Can

does the light work? Based on what the garage guys did commanding the motor to run, it would appear to point at the EBCM module as having an issue and not fully operating valves. Check the voltage going in on the c2 connector along with the grounds. Specifically, disconnect the positive and negative as the battery. Disconnect the c2 connector at the ebcm. Do a resistance measurement at the positive disconnected cable to the battery pin on the c2 connector. Likewise for ground pin. Both should read very very low (ensure that you understand what your meter "zero calibration" is for the resistance function).

Having said this, if you have never seen an ABS light before this and thus never pulled codes, how would you know that the system is "in trouble". Was the ABS recently "firing" during some brake sequence?

I'll check today, but regarding your second question I'm just trying to chase down what's causing my soft pedal and lack of brake engagement. If the ABS system is part of that, so be it. I never really had trouble with it prior to doing this brake job but my mechanic pulled codes for the ABS so

What is the c2 connector? Based off pics online I see three different connectors going to the EBCM, which one am I looking for?

 

[budwich]

I'll check today, but regarding your second question I'm just trying to chase down what's causing my soft pedal and lack of brake engagement. If the ABS system is part of that, so be it. I never really had trouble with it prior to doing this brake job but my mechanic pulled codes for the ABS so

What is the c2 connector? Based off pics online I see three different connectors going to the EBCM, which one am I looking for?

I understand.... but you also made comments about "I'll still check everything I can to try ruling out the EBCM". I am trying to help you do that. As I mentioned and you stated, that the mechanic was able to operate the motor, so it is unlikely that the motor itself is bad (its not 100% guaranteed because no pressures were measured... but likely the motor is operational).

As for the connector, I was looking at the schematics and that what is stated... I ain't an expert on GM designations.... There is a C1 connector identified going to the motor (it appears to have only 2 wires). Posting a picture of your EBCM / connection might help.

Further, as to whether the ABS is your source of the "soft pedal", the problem might be that prior to your work effort, IF you didn't know you had some codes and / or dash light, then you don't really know what the state of the EBCM was and therefore it is possible that air might have gotten into the unit. As a result, ABS activation is probably required to get rid of that air. Of course, just guess from the description. It is likely that only a tech2 will ultimately resolve questions.... that and suggested tests and checks.

 

[02FailBlazer]

Update - ABS light is functional. I pulled the ABS fuse both to check the light and to see if it changed the pedal feel with no power going to the EBCM. The ABS light illuminated and the "Service Brake System" message appeared on the dash. No change in pedal feel or brake behavior was noticed.

I also checked continuity on the ABS fuse and it appears to be good.

Pulled the pump and EBCM off the car. I don't see anything that would raise suspicion. Connector pins all look perfect, there has been zero intrusion of water or debris into any of the electrical connectors. Will try continuity testing once it's figured out where exactly I need to probe.

Pic of the pulled EBCM below.

The female connector end on the right is occupied by a male connector attached to the pump motor, which has only two wires running out of it. It seems its only purpose is to allow the EBCM to supply power to the pump when it commands it on.

The other two female connector ends on the left are occupied by male connectors running out of the wiring harness on the vehicle. I assume the one with a bunch of little pins is for data, and the other with two big pins is for power.



Regarding the pump motor, I pulled it off the valve block and there is no way whatsoever for brake fluid to enter the motor. It is completely isolated and there is seemingly no reason whatsoever for it to care at all about whatever is going on in the valve block. It isn't even mechanically connected to it, it uses what looks like a cam to actuate two spring loaded plunger things inside the block.

Pump motor cam pictured below, followed by where it mates to the block. You can see the two spring loaded plunger things that are responsible for the marks on the motor. The plungers move freely, they're not locked up.





The valves are, unfortunately, unserviceable, at least not without a lot of effort and something akin to a small machine shop. They are pressed into the block and appear to have somehow been staked in place using a metal dowel or something, hard to tell. Tried actuating them with a strong magnet and got an audible click out of all six, but I can't say what that click was. None sounded significantly different from the others.

Point being I have nothing resembling an answer yet.

 

[budwich]

I pulled the ABS fuse both to check the light and to see if it changed the pedal feel with no power going to the EBCM.

which fuse number?

ADDED: My read of things is that pulling the / a fuse does not necessarily mean that the EBCM is functioning in terms of warnings as the warning could be generated elsewhere because another module (BCM) didn't receive an appropriate message because of lack of power. Perhaps TJBaker57 might have comment. Based on reads, the EBCM should light the indicators if the coding has been set. Further, it does an initialization check every key run and speed (4 mph+). You would likely need a tech2 (or equivalent) to manually operate valves to cause fluid flow changes to check which / if any valves cause pedal changes. Can you phone a "tech2 friend"...

 

[02FailBlazer]

which fuse number?

ADDED: My read of things is that pulling the / a fuse does not necessarily mean that the EBCM is functioning in terms of warnings as the warning could be generated elsewhere because another module (BCM) didn't receive an appropriate message because of lack of power. Perhaps TJBaker57 might have comment. Based on reads, the EBCM should light the indicators if the coding has been set. Further, it does an initialization check every key run and speed (4 mph+). You would likely need a tech2 (or equivalent) to manually operate valves to cause fluid flow changes to check which / if any valves cause pedal changes. Can you phone a "tech2 friend"...

Fuse 33.

I don't know anyone with a Tech2. Might have to try buying one of the knock-offs I guess. Have I mentioned how much this sucks yet?