Check brake fluid

Coincidence. Check brake fluid and master cylinder. Check front calipers for failure, possible deployment and pressing the pads against rotors.

There is a proportioning valve in the brake line to the rear brakes top prevent rear lockup under light brakes . If you cannot get fluid through this valve then I would investigate the possibility that it is blocked/jammed or that the master cylinder rear brake section is not working ( master cylinder is in two sections with 2 pistons in case of a line failure)

Hello Patricia,

Have you checked the master brake cylinder reservoir for brake fluid loss?

I don't suspect the master cylinder as you have replaced it... but am more suspect of a leaking brake line or fitting which should have
been discovered when you had the system bled.

The only time I ever had a rear brake problem with a 2500 series Chevrolet was due to seized rear brake caliper guide pins...as your calipers are also new that is not your problem.

If your brake pedal feels spongy and travels to the floor board you have air in the system, a brake fluid leak or a failure in the power steering system, such as a broken hose, broken power steering pump drive belt, or failed pump, would result in a loss of pressure to both the hydro-boost and steering.

Find more information here:

. Hydro Boost Power Assist Systems Operation Diagnosis and Repair

Brake lines by rear door on drivers side are a common failure point. lines under door failing can cause a total brake failure. Just replace and bleed the lines.

check brake fluid level make sure brake fluid level is correct.if brake fluid level correct in reservoir.and you see abs light flashing.problem in the anti lock brake system pressure modulator valve assembly or you have electric pump and accumulator failure this is dealership fix.

faulty proportioning valve that runs off the mater cylinder

Check the fluid levels in the pressure modulator (2 black caps). Chances are, the levels are low hence the flashing brake failure lights. Best bet is to junk the ABS (they're unreliable and prone to failure) and get some custom made Goodridge hoses to bypass the ABS. Happy days.

sounds like a bad master cylinder.

That light usually has two functions: (1) Parking brake is set and (2) hydraulic brakes system failure. I would assume that you have had a failure in the regular brake system, and trouble shoot that. Check fluid level, then make sure all 4 wheels are applying the brakes. Most systems have a split, so you could get a failure of say the front brakes and still have rear, or vice versa, so you might not realize at first that you have a failure, just a longer stopping distance.

Other option is a failure (short) of the switch or wiring harness that is activated by the setting of the parking brake.

Have any repairs been made to the vehicle where the impact occurred?

My first suspicion would be that perhaps there is air in the brake lines, or maybe as a result of the impact there is a crack in one of the brake lines but I would expect that you would see brake fluid around somewhere and if it were leaking you would eventually come to a point the brakes would not work at all under any circumstance.

The first steps would be to:

1. Check your brake fluid reservoir in the engine bay and make sure it is up to the correct level.

2. Look at the left rear wheel area and see if you see any signs of a fluid leak. Be careful though, if there is brake fluid back there and you get it on the paint of the vehicle, it will take the paint off.

3. Have a helper get in the vehicle and operate the brakes while you or someone observes the left rear brake and see if you can see the brake engaging or if you see any signs of a fluid leak.