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Mike S.
Mike S., Chevy Mechanic
Category: Chevy
Satisfied Customers: 7368
Experience:  ASE Certified Master Technician
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The RR brake line ruptured. Replaced line and bled brakes.

Customer Question

Hello Don,
JA: What is the model/year of your Chevy?
Customer: I'm Sorry Pearl, the RR brake line ruptured. Replaced line and bled brakes. Now a brake wa
JA: Have you checked the fluid? How old are the brakes?
JA: What year is your Chevy?
Customer: 2000 3500HD
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: I am repairing it myself.
JA: Anything else you want the mechanic to know before I connect you?
Customer: no
Submitted: 9 months ago.
Category: Chevy
Expert:  Mike S. replied 9 months ago.

Hi, I am Mike, welcome. I'm reviewing your question.

Customer: replied 9 months ago.
Thanks Mike.
Expert:  Mike S. replied 9 months ago.

Bleed the opposite side from where you left off to center the brake warning switch but first make sure it's not the parking brake on.

Customer: replied 9 months ago.
Mike, I bled all four brakes lines.
Customer: replied 9 months ago.
E brake is off when testing.
Customer: replied 9 months ago.
Where is the brake warning switch located?
Customer: replied 9 months ago.
I would like to install bypass wire to ensure this is the switch causing the warning light to be on.
Expert:  Mike S. replied 9 months ago.

It should be under the master cylinder, the wire grounds through that switch, so you would just have to unhook it, not bypass it. If when you unhook it the light goes out, then it is the switch.

If this has hydro-boost, weak power steering fluid pressure could cause the light to come on.

I asked that you bleed the opposite side you finished up with the center that valve and switch, so you should have left off at the left front, so bleed one of the rear and see if the light remains of then.

Customer: replied 9 months ago.
Hello Mike,
I followed your bleeding suggestion, no help. I don't know how much difference it makes but I am working on a 2000 GMC 3500HD. This vehicle does have the hydro-boost system. There are no wires connecting to any part of the MC. I did locate a two wire sensor on the rear of the hydro-boost and disconnected it. The brake warning light works normally now. Any ideas?
Expert:  Mike S. replied 9 months ago.

Follow the brake lines from the master cylinder and where they go into a combination metering/proportioning valve, that is where the brake warning switch is, on that valve. It should just be the one wire.

Expert:  Mike S. replied 9 months ago.

Actually it appears there may be 2 wires, a purple wire and a black wire with black being the ground. Look on the underside of the ebcm (electronic brake control module)..

Expert:  Mike S. replied 9 months ago.

What do you mean it works normal now. If it's disconnected, that is not normal. Do you just mean when you disconnected the wires, the brake warning light went out?

Expert:  Mike S. replied 9 months ago.

The brake warning light on my Chevelle is stuck on, too. I am going to have to remove my metering valve and stick in a very thin screwdriver into the hole where the switch unscrew and center the switch.

I assume you may also have a stuck warning switch but I cannot tell you off the top of my head how to center it. I'll see if I can find a procedure, but I can say that even if you re-center it it may stick again, so I suggest you just replace it or take it apart and try to clean it.

Expert:  Mike S. replied 9 months ago.

Any updates?

Customer: replied 9 months ago.
Hello Mike,
What I mean by normally is the brake warning light is on during Key on engine off. When I start the truck the brake warning light goes off. This was as great a surprise to me as it appears to be to you. If the sensor I disconnected is the brake balance switch for the brake warning light the light should not work with Key on Engine off but it does. I am attaching a photo. The connector is easy to see I have circled the sensor on the rear of what I assume to be the combination metering/proportioning valve. Do you have a component locator which identifies the sensor. I am unable to see the color of the wires.
Expert:  Mike S. replied 9 months ago.

If you expect the light not to be on when you just turn the key on engine off, keep in mind that the parking brake wire would also have to be disconnected. If the light I out with the engine running but comes back on as soon as you hook it back up, that switch is stuck.

Expert:  Mike S. replied 9 months ago.

Don't forget to rate me well, so I get credit. If you don't the deposit you made will just sit there and I won't get my share of it.