Bleeding ABS brakes w/o Tech-1 Scan Tool?

Discussion in 'Lifted & Offroad Suspension' started by KirkW, Feb 24, 2009.

  1. KirkW

    KirkW Rockstar

    According to the factory service manual, the procedure for bleeding the brakes on my '95 Suburban is as follows:

    1. Install Combo-Valve Depressing tool J39177.

    2. Bleed all four wheels (pressure- or pedal-method) in sequence (RR, LR, RF, LF).

    3. Remove the Combo clip, then use a Scan Tool to run 4 functional tests while applying the brake firmly.

    4. Repeat steps 1 and 2.

    It seems many people (myself included) simply skip steps 1 & 3. But I've never been happy with the way the brakes feel in my Suburban. My '95 Cavalier's brakes feel much better - nice, progressive, firm. The truck, on the other hand, is slow to apply and the pedal is slow to return. I'd like to bleed the brakes properly.

    I bought a Combo Valve clip. And I have scan-tool software on the laptop that can read the fuel-injection computer, but not the ABS computer - is there one available at a homeowner-friendly price? Or is there a way of cycling the ABS without it? Or some other bleeding method that gets the air out of the ABS system?
     
  2. KirkW

    KirkW Rockstar

    Well I found out that the short answer is no - without the GM Scan Tool, you can't.

    But there are ways around it. The ABS system used on '95 through early 2000's GM trucks is the Kelsey-Hayes EBC310. It has three sections - one each for the left- and right-front wheels, and a third for the rear axle. Each section is divided into an Isolation valve and a Dump-Valve/Low-Pressure Accumulator.

    When bleeding the brakes the low-pressure accumulator is 'hidden' behind the dump-valve and can't be bled. The only way to flush the fluid and/or air from these areas is to cycle the ABS. The factory-approved method is to use the Tech 1 Scan Tool to command the computer to cycle the ABS.

    But the "shade-tree" mechanic method is to drive down a gravel- or snow-covered road and jump on the brakes, which will cause the wheels to lock up and... cycle the ABS.

    There's an obvious flaw in this procedure - one has to get the brakes working well enough to safely drive down said road. Plus, when the ABS cycles any air in the accumulators will be dumped into the lines. This may have a dramatic negative affect on your braking ability. Assuming all goes well and you were able to get all three circuits to activate (LF, RF and one of the rear wheels), then it's time to gingerly drive back home and bleed the rest of the air out of the system.

    You can read more about bleeding ABS brakes here:

    Brake & Front End Magazine, "Bleeding ABS Systems" by Bill Williams (July 2005)
     
  3. TRPLXL2

    TRPLXL2 Epic Member 5+ Years 1000 Posts Platinum Contributor

    Actron just came out with this ABS reader, it gives you a code and detailed description for $229. I bought one to go with my Auto X-Ray scanner, and those two things pretty much cover all bases. You are right though you still have to get the system reset in order to operate those valves, but the scanner is still a nice thing to have anyways. :party:

    http://www.gmtruckclub.com/forum/attachment.php?attachmentid=2059&stc=1&d=1235879062
     
    Last edited: Mar 3, 2009
  4. KirkW

    KirkW Rockstar

    I'm interested in your review of that device.

    One problem I had was trying to read the ABS and TCS codes on my wife's 2000 Pontiac Grand Prix. In theory, any ODBII scanner can read engine as well as transmission and brake codes (they're all in the OBDII specs and the codes are defined).

    But in reality only the engine-codes (i.e. - emissions-related stuff) are mandated by law. So the manufacturers are free to chart their own course on the other stuff - and frequently do.

    So with my wife's car we had to go to the dealer to get the codes. That, combined with the trouble-shooting in the service manual leads me to believe the ABS computer has failed. Still, I would rather have spent the $100 the dealership charged for diagnosing the problem on a scan-tool of my own.
     
  5. TRPLXL2

    TRPLXL2 Epic Member 5+ Years 1000 Posts Platinum Contributor

    Here is a little info on the Actron ABS Brakescan:

    This affordable alternative for diagnosing brake problems displays ABS trouble codes and definitions on an easy to read backlit display. ABS Brakescan eliminates guesswork and helps identify the parts required for brake repair.
    Systems diagnosed include wheel speed sensors, ABS solenoids, the brake control module, ABS pump motor, vehicle speed sensors and more.
    This simple to use scan tool plugs into the vehicle's OBD II port and provides coverage for most OBD II domestic vehicles 1996 and newer (GM, FORD, and CHRYSLER). ABS Brakescan is updatable online, features an ABS code library, retains the most recent vehicle scan, and has intuitive help screens.

    ABS Brakescan includes: CP9449 handset, detachable vehicle cable, a durable/soft carrying case, and a quick start manual. Optional battery power enables ABS Brakescan to save and view data when not connected to the vehicle.

    I typed this directly from the introduction page of my booklet, I couldn't get it to down load. I am like you KirkW, even if I can't fix it I would still like to be able to diagnose it and sometimes actually be able to fix it. It is brand new to the market so there are still some bugs they need t work out, but I have already used mine twice and I have only had it a month. Hope this helps you out, and I know you won't regret the purchase.:great:
     
  6. daveingland

    daveingland New Member

    So, stupid me decides to replace the brake booster and master cylinder in a '99 Yukon and then try a conventional brake bleed sequence. After going through 5 bottles of brake fluid and only getting to the second wheel, I figure there must be a problem. When the brake pedal is depressed, I can hear bubbling sounds in the ABS modulator. It has 4 wheel ABS. I search and find that the only way to get air out is to use a GM scan tool through the dealer. However, I can't even do the conventional brake bleed because there are so many air bubbles in the lines.

    I've seen workaround posted like the one above that talks about getting the ABS to be locked up on a gravel road as well as just turning on the ignition and bleeding that way. Can anyone confirm if either of these really works or if there is a better way? My problem is with air in the brake lines, taking the Yukon out to a gravel road isn't really feasibly with so much air still in the system.

    Hoping someone can help so I can get this finished. Been without the car for going on 4 days and had no idea the job would be so difficult on the Yukon. Thanks!
     
  7. 2COR517

    2COR517 Epic Member 5+ Years 1000 Posts

    Dave - you might just try using gravity to bleed the system. It's not fast, but will work. I have a friend who does auto work on the side, this is what he does. Just crack the bleeder, and let the fluid drain down, keep the reservoir full.
     
  8. daveingland

    daveingland New Member

    I'm not 100% sure, but can't see how gravity bleeding would rid the ABS modulator of air. I think it needs some kind of pressure from actuating the internal valves or something like that. I'm just not really familiar with ABS and wasn't prepared for having to bleed that part of the system.
     
  9. 2COR517

    2COR517 Epic Member 5+ Years 1000 Posts

    It might help you bleed them enough to take it out on a gravel road and actuate the ABS pump.
     
  10. daveingland

    daveingland New Member

    Since the rear and front brakes are on different systems, I decided to go ahead and try bleeding the front brakes. Those were easy and I think I got the air out. Tested the brakes, but the pedal goes to the floor before the brakes catch. So, at speed drives may be tough. However, I may consider seeing if I am brave enough to give it a shot.

    It seems like the back brakes were the problem with air in the system. Hoping I can find some fix for the pedal feel at this point so I can avoid having to go to the dealer to bleed out the ABS modulator. Of course, I have no idea even if that is all that expensive or not. I'll call the dealer on Monday if I can't get the gravel road to work.
     

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