I have been having a couple of problems lately that I think are connected. First this is on a 2003 Blazer 4.3 4x4. First problem the Brake and ABS light comes on periodically. The A/C will change from dash to defrost when there is a load on the engine. Sometimes the vent control wont work properly. I thought the A/C issue was vacuum related. So I started tracing the vacuum lines and replacing them (under the hood first). What I found was brake fluid in the vacuum lines between the ABS box and the firewall. What causes this? What do I need to do to fix it? Are these related problems?

 

Been scratching my head reading this one.... There are NO vacuum lines between the ABS controller and.... There's no vacuum line running to the ABS unit - period. Vacuum related problems will definitely cause the heater problems you describe. If you're talking about the 3/8" vacuum line running between the brake booster and motor and it has brake fluid in it that means the master cylinder is bad and losing fluid out the rear seal and also the booster is ruptured internally. It's sucking fluid up the vacuum line into the motor and it can migrate to all the other lines. Post a picture of this "ABS controller" with vacuum lines.

 

nice diagnosis!

 

I'm have the same problems with a 96 jimmy..I think it may be transmission fluid though. My vacuum canister was half full of it. The 4x4 won't ingage either, the light flashes a couple times then nothing.

 

Ok, your problem is different. Bad vacuum switch on transfer case is sucking fluid out of it.

 

Maybe I am calling it the wrong thing. The Brake lines coming from the master cylinder goes into this "thing" then goes out to each caliper or wheel cylinder. There is a small vacuum line that goes to or under this "thing". There is a T beside this, one end goes to another T one side goes to the motor intake which has a one way valve in the line.

I cannot post a picture as my home computer is down and work has no access for uploading pictures.

 

While you're blazer is quite a few years newer than mine, I can assure you any ABS valve assembly that I've seen from GM does not have any vacuum line going into it. All of the solenoids that operate the dump valves etc, are electrically controlled. Perhaps you have an improperly routed vacuum line.

Regardless you're vents not working properly is a sign of a vacuum leak, you'll need to track that one down, but it's much easier to do with a hand held vacuum pump like a Mityvac, which I've seen some people mention in here before. Using the search tool on this forum will provide you plenty of information on the vacuum line routing and diagrams to boot.

If you're getting brake fluid in you're vacuum lines, you should see the fluid level in your master cylinder going down. A more common occurrence on these vehicles is for the transfer case vacuum switch to fail and leak whatever fluid is in your transfer case into the system. You'll need to find out what kind of transfer case you've got, that will tell you whether or not the vacuum switch is even on the transfer case, as well as what fluid is in it. You can either search around on here for the information on how many buttons you're 4wd controller has, or you could just climb under and read the tag. You'll be looking for something like "NP 233"

You'll need the codes from the ABS to begin the diagnosis. If I'm correct though no typical OBD-II scanner can get to those codes, I could be wrong on that though. Anything ABS is above and beyond me apart from swapping out the controller.

Good luck.

 

I just replaced the vacuum switch on top of the transfer case and I'm still getting oil into these lines. From my understanding, you have three connections that go to the top of the transfer case: 1. Vacuum supply, 2. the vacuum line that goes to the actuator under the battery, 3. a vent line that allows the actuator to release its vacuum once in 2 hi. My question is, "is there even a divide between the oil in the transfer case and these vacuum ports"? This is a brand new switch and they don't even provide a diagram for what goes whear. I was thinking that that the large port on the vacuum switch was for the vac supply, the middle port (top of the apex in refferance to the "dot" so to speek that allows you to only put the plug for these lines on the vacuum switch one way) and the vent line. Another question " does this vent realy vent the actuator when you go back to 2hi or is it there for the venting of the transfer case"? Not unlike how theres vent line on a transmission. This is driving me nuts. Thank you for your time if you read this.
Mike.

 

Two things have to happen for fluid to get into the vacuum lines. #1 - a bad input seal on the transfer case & #2 - a sloppy vacuum switch on the transfer case. Even with a new switch, if the transfer case is still cram full of fluid being forced into it by the transmission, you may still be getting fluid in the lines.

And even after you have repaired the conditions causing fluid to get into the lines, a thorough cleaning of the lines is necessary to remove all of the fluid. If the condition was prolonged, fluid could be up into the vacuum diaphragms in the HVAC system and throughout the entire vacuum system.

The vent line to the switch vents the actuator into the same line used for the transfer case vent.