'08 1500 Z71 - Brake help

[Tynee]

Evening gentlemen. I'm a new face to this particular section fot he truck board, but I've been around forever, so I'm lookign forward to getting to know the folks over here.

I just bought an '08 Silverado 1500 CCSB LT Z71 5.3 auto. It's a bit of a basket case right now. I'll be abck asking about engine codes in seoarate threads, but tonight my question is brake related.

1) My truck has RPO code JL4 - Active Brake Control, if I've done my research correctly. What is ABC, and what does it do for me?

2) More importantly, possibly related to 1), possibly not...I have zero brake pedal response. It doesn't build any pressure. I replaced the master cylinder (with a proper bench bleed and a power bleed at all 4 wheels) and took the rear drums off to make sure that they were properly adjusted. These 2 steps helped a LITTLE. Now I can build pressure by pumping it, but it goes away the next time I release the pedal. Am I having an ABS issue? No ABS light to indicate that. I'm a little lost here.

Any help would be appreciated.

[Tynee]

After a little more reading, I'm given to understand that there is a link between the throttle body and the Stabilitrac/Traction Control Systems on these trucks. One of the other problems I was told this truck had before I bought it was a throttle body issue. Not sure the code, I've been chasing the brake problems first.

Is it possible for problems with the Throttle Position sensors in the throttle body to cause problems with the stabilitrac and traction cotrol systems, that would in turn casue tthe brake pedal problem I've got?

[Special-Ed]

you do know a couple hundred buck at a dealer and your issues can be pinpointed and fixed...

the local dealer will diagnose for around 130 bucks... keep that in mond... what is your yime and energy worth

[Tynee]

Were you aware that the average cost of having a check engine light diagnosed and repaired at a shop is $367 and change?

So far I've spent $100 on a M/C, yes, but I don't feel bad changing that when the truck was exhibiting the classic symptoms of bad M/C, and the PO's shop told him it needed to be changed.

If I run down to the dealership and drop $400, what have I learned? Can I fix this problem myself in the next truck with similar symptoms?

Thanks for your input, I guess, but I'm not ready to throw in the towel just yet.

[Special-Ed]

i just brought my truck to the dealer to diagnos blend door motor issues with my climate control... it was 130 bucks.. hooked scanner up checked all my motors checked firmware of the bcm

in 30 minutes the dealer can run the abs motors and check for issues, hell it might even be a recall... stabilitrac and traction control all work hand in hand with the abs... and without the scanner at the dealer all you are doing is wasting time and money with a shot gun approach. you also need to be able to check each wheels speed sensor... my point is talk to the dealer, see how much to just troubleshoot... then you can decide....

they told me what the issue is, parts are on order from a real parts store 130 bucks saved me 5 hours of ripping the dash out and having an inop truck for 3 days...

in all honesty, had i a scanner like the tech2 or whatever its called i could have done the same thing... but i have yet to find a non gm bcm scanner that can do what the dealer can do...

i used to be an engineer for pontiac many moons ago.... just because i can doesnt mean i should or would....

[Tynee]

Ed,
I'll take it under advisement, but it runs against the grain to run to a shop, especially the dealer, every time the slightest little issue develops. If that is what it takes to run a modern vehicle, maybe I should just stick with my '70...

[Special-Ed]

Originally Posted by Tynee

Ed,
I'll take it under advisement, but it runs against the grain to run to a shop, especially the dealer, every time the slightest little issue develops. If that is what it takes to run a modern vehicle, maybe I should just stick with my '70...

updates? is truck still sitting? did you fix it?

[Tynee]

No update, been a hectic week at work. I've done some other little stuff that the truck needed, cleaning it up and taking the grille gaurd off the front end, etc... I plan to replace the bleeder valve that I stripped after the M/C install, finish a thorough brake bleed and asses my situation on the brakes.
I did plug a code scanner in to it. Codes indicate the TPS is a problem. I plan to clean the throttle body and re-install before I buy a new one, since it doesn't cost anything. I'll then be able to better assess my situation on that front.

[Special-Ed]

Originally Posted by Tynee

No update, been a hectic week at work. I've done some other little stuff that the truck needed, cleaning it up and taking the grille gaurd off the front end, etc... I plan to replace the bleeder valve that I stripped after the M/C install, finish a thorough brake bleed and asses my situation on the brakes.
I did plug a code scanner in to it. Codes indicate the TPS is a problem. I plan to clean the throttle body and re-install before I buy a new one, since it doesn't cost anything. I'll then be able to better assess my situation on that front.

make sure to clean the idle circuit very good. the pintle and seat as well on the iac

[95 S_Trucker]

I see you are able to scan the PCM. Do you have a scanner capable of communicating with the ABS? Check for codes.

Originally Posted by Special-Ed

make sure to clean the idle circuit very good. the pintle and seat as well on the iac

I was un aware that the drive by wire trucks had an IAC.

[Special-Ed]

Originally Posted by 95 S_Trucker

I see you are able to scan the PCM. Do you have a scanner capable of communicating with the ABS? Check for codes.




I was un aware that the drive by wire trucks had an IAC.

oh man, now i have to look... my suburban is fly by wire, i just natuarally assumed it has an idle circit. idle is idle and not throttle... if your not learning..your dead!

[Tynee]

So, I removed the TB, cleaned it thoroughly, and reinstalled. During the removal process, I found a hose disconnected that should have connected the air intake to the passenger valve cover (is that the PCV valve in these trucks?). After reassembly, all codes cleared. Idle is a little funny, but I performed a "relearn procedure" that I found online, and it improved the idle. I understand that it will continue to improve over the next couple hundred miles of driving. If not, the Tech II relearn is always an option.

My brake problem is a little more concerning. After replacing the stripped bleeder and a thorough bleed, the brakes build pressure, but the pedal still isn't as firm as I'd like. I guess I'm going to drive this for a while, and watch the fluid level. I can't find a leak, but the brakes act like that's the problem.

[GMCJOE]

Take it to the dealership or another shop that has the scan tool for the brake system. That will be the only way to get all the air out of the system. The ABS/ABC system has to be cycled.

[Tynee]

Originally Posted by GMCJOE

Take it to the dealership or another shop that has the scan tool for the brake system. That will be the only way to get all the air out of the system. The ABS/ABC system has to be cycled.

That makes sense. I've gotten enough air out to make it safe to drive. The brakes are a little soft, but one good pump makes them rock solid. I figure that over time the air will work it's way out of the sytem. If that doesn't turn out to be the case pretty quickly, then I'll hit the dealer.