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I have a 2003 Chevrolet Avalanche with a broken brake line. We replaced the broken brake line, added new fluid and bled the brakes for about an hour and there still seems to be air in the lines or something else because the brake pedal still goes to the floor. The brake service engine light comes on every time we release the pressure in the lines. Is there something else that could be wrong or is this normal to bleed this long?

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    Did you start bleeding the brakes from the furtherest line to the master cylinder? You start with the passenger rear > driver rear > passenger front > driver front. Are you bleeding by hand or using a vacuum tool? – Hᴇʀʙɪᴇ Mar 28 '16 at 20:35
  • I do not remember if you can scan the code but have you tried hooking up a diagnostic computer to see if the brake system is throwing an error code? – Hᴇʀʙɪᴇ Mar 28 '16 at 20:44
  • Bleeding by hand & would I need to have the brake service soon light on to check it? – Wvjennifer Mar 28 '16 at 22:06
  • Instead of wasting a lot of time bench bleeding and pulling things apart you're better off having the truck towed to a shop so that they can bleed the bypass modulator valve. They might charge an hour labor and fluid. – Ben Mar 29 '16 at 21:17
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I have a 97 suburban, so I believe things are very similar. I too have replaced lines on this truck and spent hours of time and over a gallon of fluid trying to get it bled correctly. A couple things that I've learned and have helped.

Bench bleed the master. Remove the lines, install short lines, and have them go back to the reservoir on the master. Pump until no bubbles.

Bench bleed the ABS. Same as bench bleeding the master. I didn't try this, but I think it would have really helped.

When bleeding - Open the bleeder, push the pedal down, close the bleeder, release the pedal. This will help from air getting trapped.

A couple methods I've used:

Normal pump bleeding. Never quite got it right. I wasn't closing the bleeders in between pumps though.

Pressure bleeding - apply pressure to the master cylinder reservoir to push fluid through. Might had worked had the top been able to seal well, but it ended up just making a big mess.

Vacuum bleeding - apply vacuum at the bleeder. Be sure to use a ton of Teflon tape so you don't suck air from around the threads.

Reverse bleeding - Push fluid from the bleeder back through to the master.

I ended up modifying some bleeders by cutting the tip off so I could screw it all the way down to ensure no air would get past the threads. Used a ton of Teflon tape. Vacuum bleed until I purged the line, reverse bleed, install original bleeder, vacuum bleed until I don't see bubbles.

I think the reverse bleeding helps get the bubbles out near the master/abs where there is a long drop. The bubbles want to go up, and normal methods are trying to push them down. I might had had good success with bench bleeding the ABS first also.

You should also note, at least on my truck, part of the process is to have the dealer run an automated bleed on the ABS system. This takes a very specific scan tool. I tried several of my cousin's professional Snap-On scan tools, and they were not able to do the ABS bleed.

  • What software version are they running? Every Snap-On scanner I've owned since the original Solus has been able to activate the Bypass Modulator Valve. – Ben Mar 29 '16 at 21:15
  • I don't know what version or what model the scanners were. I tried 2 or 3 scanners of different brands. They could send/receive from the ECU and read from the ABS, but couldn't do the automated bleed. At least I didn't see the option for it. – rpmerf Mar 30 '16 at 19:44

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