Brakes not working properly

Good afternoon,

The ABS is a system that prevents wheel lock-up when braking heavily. When there is a fault in the system, the ABS is offline. When it fails you will always have normal braking power. You will not lose the brakes if there is a fault.

https://www.2carpros.com/articles/abs-warning-light-on-easy-repair-guide

I attached a description of the system and how it works below for you to view.

Roy

Thanks for the information - not quite sure what to do with it. The ABS light is not on.

The ABS will not kick in unless you are in a panic stop and one of the wheels is locking up. Then it will activate and prevent the wheel from locking up.

It does not work under the normal operation of the brakes.

Roy

Well maybe it's not the ABS. all I know is that for example; I needed to pull it out of my driveway onto the street in front of a car this weekend to give it a jump start so in effect I was moving very slow and as I got close to the vehicle and went to stop it wouldn't stop and then I had to jam on the brakes really hard. I'm not sure how else to explain it. There are no visible leaks, reservoir is full, no ABS or Brake Light is on.

This sounds like the pedal may have gone down and you had to push harder to get it to start.

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

The seals inside may be failing especially when you push it very softly.

If you replace the master cylinder, make sure you bleed and flush the brake fluid. Old brake fluid will cause this as well.

Roy

I changed out the master cylinder today... bled it, then bled all brake lines in pattern from back right/left, front right/left. took it out to drive it and the pedal still feels the same and if I have to stop suddenly the pedal drops to the floor and it almost feels like it surges. No brake lines are open or leaking.

How did you bleed the ABS? That requires a scan tool to bleed it. If you did not, you will have air in the system and that will cause the pedal issue.

I attached the procedure below for you.

Roy

Well, given I am no mechanic thus having a scan tool that step was not completed.

Would have been nice to sort this out but that is not going to be the case absent taking it to the dealership.

I see there is a plethora of scan tools listed on Amazon but I'd have no clue which cheap option would allow for this procedure.

I know absent doing this there is still air in the line. I was using the bottle method with the bottle 1/3 full connected via a tube to the bleeder and I would gently pump the pedal about 5-10 times, at least to see the fluid color shift and then would move onto the next caliper.

You could take this to any repair shop. They have the correct scan tool to perform the procedure for you.

It will be much cheaper than going to the dealer. The usual charge is $50.00 to $75.00.

Roy

Well I bought scan tool - Foxwell NT630 and proceeded to bleed the brakes again.

The scan tool really didn't have a workflow that stepped through each brake line. Rather it would basically say to get it ready, I would open the bleeder which is connected to a hose into a bottle with brake fluid, I would get back into the vehicle and it would say to press and hold the brake - the ABS then would cycle several times and the workflow in the scan tool would end. Without lifting up on the brake pedal I would keep it held down with a DIY bar. I would go close the bleeder and then proceed to the next line set.

after all said and done, I cannot feel a difference - still plenty of pedal movement and spongy.

Not sure where to go next on this....

Okay, when you did the automated procedure, all the bleeders should have been closed. By the description you posted, you left the bleeder open in the rear.

I would rebleed the system again with the scan tool and keep all the bleeders closed.

Roy

Okay, so herein is my lack of experience.

Are you saying that what I should have done is the bleeding through all four wheels; back right, left, front right, left?

After that part then do the automated bleed with the bleeders closed?

I just presumed that was the entire point of the exercise was that the ABS pump would auto bleed and to do so I needed to have the bleeder open at the time the scan tool told me to push and hold the brake pedal, then repeat for each wheel.

Okay, you to just do the automated sequence with all bleeders closed. Do it several times since you did it with open bleeders.

Then do your manual bleeding.

Roy

May I ask why the automated before the manual bleed?

You can do it the other way but that is what the manufacturer recommends.

Roy

One last question... is it fair to say that some vehicles, not this suburban year, would have a scan tool work flow that is guided through each wheel? I ask because I have watched a few YouTube videos and see where the scan tool work flow directs the user to each wheel but in my case I only have one option in the scan tool and the workflow is just to hold the brake pedal until it cycles and the workflow ends. Or is this more so related to the type of scan tool, meaning mine is a cheap version compared to professional grade scan tool?

I know the YouTube video you saw. That is inaccurate. The tool opens the valves and vents the air from the module. The basic bleeding does not go through those areas.

There is never a need to open bleeders for the automated sequence.

Roy

Roy, I ended up having the GM dealership take a look at it and they said they had to bench bleed, and then do the scan tool, manual bleed, yada, yada. they just returned to me.... Brakes feel the same. I back into my driveway and they had pulled it in so when I went to turn around the vehicle to pull forward and I was barely moving and put on the brakes it did the same thing, didn't want to stop and the pedal surged quite a bit....

On a side note: I primarily had it there because I noticed a power steering leak and while they inspected they found a coolant leak on the down side hose from the overflow.... Curious to know if you can comment if this cost is in the ballpark of average or did I get overcharged ? Power Steering High Pressure Hose $129.95 and the Coolant Hose was $122.95 and all told with labor it was $566.53.

I am going to retire this vehicle to anyone who will give me a few bucks for it....

It was good vehicle for me for the past 8 years... time to move on to a newer vehicle... different problems : )

That is a shame that they gave it back to you with the same issue. They should have pursued the reason and given you possible resolutions for the problem.

This is the state of our technicians today. They sometimes have no idea of the cause of the issues and their lack of knowledge becomes the customer's issue.

Hope you have better luck with your replacement truck.

Roy

Roy, still driving it. my purchase of a new vehicle is on hold.

So I want to continue to troubleshoot this brake problem.

Could it possibly be the brake booster?

As far as repairs for the brake system... last winter had a brake line burst in the back by the axle per the GM dealer which they fixed. I replaced both rear calipers. Lastly the master cylinder recently.

When driving it again today the pedal surges at the end of the stroke as the vehicle is coming to a stop. when it surges like this it allows the vehicle to move more forward than originally intended if that makes any sense.

That is the ABS activating when it should not. When the ABS activates it pulses fluid to the wheels for stopping. The unit itself could be the issue

You need to match the number of the unit for replacement and it needs to be flashed when you install it for it to work. Without flashing, you cannot bleed it and the system will not work.

https://www.2carpros.com/articles/how-to-replace-a-abs-controller

Roy

Could it be an issue with an ABS Wheel Sensor?

No, a sensor would not cause a low pulsating pedal.

Roy

Absent the pulsing at the end of the stroke when pedal is pushed. would it also cause the pedal to be soft/spongy/lots of travel before feeling the brakes kick in?

Yes, the ABS control unit can cause that issue. There is air that is not being bled from the unit itself.

Roy

Roy, still tinkering with these brakes... I came across this video and the way he describes it is exactly what happens. https://www.youtube.com/watch?v=0_bglkgERWM

Are there only these sensors on the front or on all four axles?

I guess it couldn't hurt to check the rust and clean them up and give it a try.

The control module is more than I want to spend since I am trying to sell the darn thing.

Not sure if the sensors can be salvaged or I just need to remove the old, clean the rust and install new ones.

However, I understand the spongy pedal may still be the air and ABS control module issue.

I put my scan tool on it and had it read.... I got this back:

C0265 - seems you nailed it of course...

I am wondering if I can even attempt this or it needs to go to the shop.. I know my GM dealer is going to be expensive.

One thing to note... not that it make any difference but my abs and brake light on the dash are not on and never stay on... (so is the a soldering issue or maybe something else) ?

I would just replace the module. I would not do anything internal to it unless you have the equipment and experience in that kind of repair.

Roy