Since it was in the 30's all day, I took that as a sign that I should get my ABS and 4WD problems fixed before snow.

Two weeks ago, my ABS light began coming on. It didn't really affect braking under normal conditions, but at low speeds while braking during a turn, the ABS would kick in for no reason. After researching, I found that a common problem was the gear that the front speed sensors use will often get dirty, which impacts the speed signal confusing the ABS system into thinking the wheels are slipping. So I disassembled the brakes, removed the sensors, and cleaned them up. The front passenger's side was immaculate to begin with, the front driver's side was a little dirty, but it didn't appear to me that it would cause my problem. I also cleaned and applied di-electric grease to the speed sensor connectors. None of the wires appeared broken or crimped.

I suspect that air could be a culprit, but cannot find a bleeder screw on the ABS unit itself (my Z has two bleeder screws on the ABS unit). I believe it'd have to have a bleeder screw somewhere near the ABS unit (since air rises, every brake system I've seen has one high up, in addition to each at the calipers), so can someone tell me where one might be or if I'm simply mistaken?

Also, could bad/old fluid cause the problem?



As for the 4WD, I disconnected the vacuum hose on the vacuum solenoid (on the firewall) and checked it for pressure as the 2Hi button was pressed (that's what the writeup I came across said to do). It had vacuum, so I'm assuming that means the vacuum actuator on the transfer case is bad, correct? If so, is this the part I need?
http://pro.chevypartspro.com/buy.php?make_text=chevy&ml=blaz-4{embeddash}door-002&model_text=blazer&year=1999&part_n ame=4wd_actuator&brand_name=dorman&s=1&amp ;my=1



Thanks in advance for any help - I rely on my Blazer heavily, and when winter is here, ABS and 4WD are things that will make my life much easier.

 

Also, why is every one of my apostrophes turning into quotation marks??

 

They are not turning into quotation marks, they are multiplying. This is all due to an attack on the server that happened quite a while ago.

As far as the 4wd issue, if you are getting vacuum even in 2wd mode, then the vacuum switch on the transfer case is the most likely culprit, not the encoder motor (or actuator as the link states).

About the ABS issues.. There is no bleeder screw on the unit. You can bleed through using normal bleeding procedures, but if you are thinking that there is air the ABS unit itself, then you need a scan tool to bleed it.

If bleeding the brakes does not work, then it is possible that the ABS unit itself is at fault. Without accessing the ABS control module with an appropriate scan tool and running testing and due to the high cost of the ABS unit itself, you should not just go replacing it. Another possibility is broken, pinched, or otherwise disconnected wires in the front speed sensors.

 

Thank you as always. I'll take the Blazer somewhere to have the ABS system diagnosed - I figure I've done about all I can do without the scan tool (damn these modern cars). If you're not too busy, could you link me to the vacuum switch somewhere? I've checked a few sites for that part and can't find it. (Or at least let me know what the part number is so I can call Chevy?)

 

DORMAN Part # 49315

On an unrelated note, please include your vehicle information in your signature for us to reference. It makes it a pain to have to go back through your old posts to figure out what it is that you are driving.

 

My mistake - I thought I included that in my original post (I normally remember to do that). Thank you very much!

 

Go into your board profile, and you can PERMANENTLY add it to your signature.

 

OK, I just figured I'd verify my issue before getting underneath the car in the snow to fix this 4x4 problem once and for all.

I picked up the vacuum switch for the transfer case (part number 49315 as suggested). I was under the car trying to find it, couldn't, so I decided that I'd research where it was later to find it so I can fix it. (Then I found http://i11.photobucket.com/albums/a1...ada/t-case.jpg so now I know where it is for when I go back underneath the car.) However, as I'm sure you can understand, I want to make sure this is going to fix my problem (especially now that it's snowing out).

I took the Blazer to a Chevy dealership to pull codes (nice dealership, too... they didn't charge me). (Turns out the ABS problem is the front right speed sensor.) They said the 4WD code was from the switch on the firewall. In the hopes that it'd be that easy to fix, I bought that part and replaced it. It did not solve the problem. Since this is the device used to diagnose the vacuum switch that I previously bought, I assume that if that switch is, in fact, faulty, it would be the reason the code was coming from that device (on the firewall)? If this is the case, then I can be reasonably certain that replacing the switch on the transfer case will solve my problem, right?

Thanks in advance, and I hope this is the last time I have to ask about this pesky problem.

 

If you have the electric solenoid on the firewall, I do not think you will have the switch on the transfer case. But you have not stated yet if you have the 4-button, Auto4wd option even though this pretty much confirmed by the electric solenoid on the firewall. I missed the presence of the electric solenoid on the firewall initially.

If you can tell which vacuum line runs from the solenoid to the actuator under the battery, the other vacuum line should have vacuum pressure at all times and be connected into the intake manifold somewhere (I cannot find a diagram).

As far as your ABS issues, I just read a TSB on this condition and it had to deal with the air gap between the sensor and the reluctor ring in the bearing assembly. You need to sand down the pad the sensor mounts to, closing the air gap. Do this in steps. Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel by hand between each step. The voltage should now read at least 350 ACmV's.

 

I have the automatic transfer case.

And thanks for the advice on the sensor. It's under warranty (I replaced it in March) so I'm going to try to replace it, but if they gave me any problems or I ever encounter the issue again, I'll be sure to try that.