RenHoek

My rear antilock light has been on for the last 6 years or so....no biggie.
About 2 weeks ago, I had to stop quickly on the highway in traffic, and the brakes "faded" for about 1/2 second, then came back on hard! I glanced down at the dash right after that, and caught the antilock light coming on all of a sudden. Since then, I've noticed that occationaly, when I start up the truck now, that light will be off for about 10 minutes, then come on (as usual). The problem is that during that 10 minutes, if I have to slam on the brakes, they'll do that fun little fade trick again, and the light will come back on.

It's like the CPU forgets that the ALB system isn't working, until you test it, then it says to itself "oh, ˟˟˟˟˟, that's right...ALB doesn't work...I'd better ignore the fact that I have it and just break the old fashioned way..."

The brakes work nice and predictable when the light is on, but watchout if the ALB light is actually off!

Anybody got any ideas about this? I'd like to get this fixed before cold weather comes to my garage...

I tried to measure the sensor a long time ago, but I couldn't get to it - its connector is hard to get both hands on to disconnect, way up in a tight spot to reach, so I gave up.

Also, I put OME springs/shocks on this about 3-4 years ago, which raised it back up to be level again (about +2.5 inches) and added an extender-bar to the ride-height load-leveling mechanizm at that time. (this is just for info, since it didn't change anything at that time...)

Thanks!
RenHoek

MRunner

you may have 2 seperate problems here.
1) the rear anti-lock speed sensor (expensive replacement)
2) something else with the brake system (seperate from the ABS). Regardless if the rear anti-lock is working, your brakes should operate unaffected, as they're a mechanical system, aside from the power assist.

RenHoek

I guess that's what I'm fishing for - info about how the rear ABS works on these. My first instinct was that something was going wrong with the brakes, but then I've noticed that it only has the problem when the ABS light is off, and it immediately comes on after the hiccup. I figured the system is TRYING to do something that normally (with a working system) would be more effective at braking than it currently is, and when it detects that it isn't working, it switches over to a normal power-assist mode....just guessing....It's been 100% stable (non-ABS) for the last <many> years, and the light has been 100% on all this time, too.

Does the CPU pulse the rear brakes on these when it detects skidding?

MRunner

I don't know exactly how the ABS works on these, I assume its like most conventional systems where the ABS has its own control unit monitoring wheel speed and pulsing the wheel cylinders/ calipers on lock-up (or close to).

If my rear anti-lock light isn't already on startup, it comes on within 10-25 minutes of driving. On mine, braking with or without the light on is normal. Even during braking if the light comes on theres no change.

Elton

i would have it checked out to be safe

RenHoek

To throw some info on my own post (helping future searches...)

I found some good details here:
http://www1.autozone.com/servlet/UiB...3d801625f2.jsp

Apparently, the ABS system uses the PS pump to pump the rear brakes:
A significant difference in this system (from 4 wheel ABS) is that power steering fluid is circulated through the brake system actuator. The ABS control solenoid acts on the power steering fluid, not the brake fluid circuit. The power steering fluid acts as a control pressure circuit, moving pistons and valves within the actuator which control the brake fluid circuit.

I've noticed that I have a PS fluid leak, so maybe that's what's causing the rear ABS fault in the first place...time to dig into the trouble codes and see what's what.