'99 Blazer ABS light is back.
 

Seems we are having issues with the ABS light coming on in our '99 Blazer 2 door 4WD.

It's random at this point.

We dropped it off at the shop on Monday, but they couldn't get the light to come on and said they couldn't find any codes to see what was causing the light.

Of course, the next day, it's back on.

We had this happen about a year ago and had both of the hubs replaced.

Anything we can check before we try to take it back?

The weather was cold when we took it in, no light. It was warm yesterday and the light was on all day and this morning.. Now it's colder on the way home and the light isnt on.

Without the trouble code, it's tough to narrow it right down. Wheel bearings are still good? Connections to the wheel sensors corroded/damaged? Speedometer works properly?

I'm not noticing any issues with the bearings, havent checked the sensors.

I was hoping that was the case since the bearings are still under warranty, but can't get them changed out w/o the trouble code showing them as faulty.

No issues with the speedometer.

Guess I'm hoping to be driving an Autozone or something like that when the light is on and see what they can pull.

My 99 ZR2 seems to do the same thing but the light comes and goes when it is warmer. It will be fine through a few brakings and then it makes that funny noise, the pedal vibrates with your foot on it and then the light will come on and it acts fine. Sometimes I can hear something which I assume is the pump under the hood when the brakes are not being used. When it's cold it stays on most of the time. Thinking about just pulling the fuse.

As the ABS seems to be a common issue, I've been doing a bunch of research on it so when my 04 starts having issues I'd know what to look for.

From what I've been reading, an intermittent problem is usually one of a couple different things. The most common seems to be a broken wire on the hub, or solder connections in the control module have vibrated loose. Both are affected by motion and weather conditions.
Are you SURE it didn't produce a code? Most "backyard Mechanic" readers aren't capable of reading abs codes. It would help to narrow down the issue with a code as a starting point.

I'm just going by what the head mechanic told me.

They are one of the bigger shops in town so I would hope they have the proper equipment.

Well if they have a decent scanner like the MODUS from Snap-On they can read each of the wheel speed sensors. At that point they can determine if one if acting up. You can also record and graph them.

Good information. I have recently replaced a bad front hub thinking that would take care of the problem but nope. Can you get to the solder connections or is it just better to replace the module. Junk yards are full of them and many are being parted out on CL. Also on older models there was wires running back to the rear wheels for the ABS but on my ZR2 I see no wires. What controls the rear or is it done at the master cylinder or something?

my2K , not trying to hi jack your thread but it seems we have the same problem. ABS is nice in bad weather but not essential. I was just going to pull the fuse if I can't find the problem. However it doesn't appear to be that hard to solve. If I find it I will let you know. I think RJ2 is on to something with the solder joints as temperature would cause wires to move. You might try going to Auto Zone and have them do the test if the light comes back on, it's free.

The ABS performs a self test each time the ignition is turned to the RUN position. When vehicle speed reaches ~5mph, the wheel speed and vehicle speed sensors, and their circuits, are checked. The ABS pump is also activated for ~2 milliseconds. If no problems are detected, the light stays off.

Wheel speed and vehicle speed sensor DTC's are "latched DTC's" meaning when there is a malfunction, a DTC is set in memory, and the ABS light comes on. AND, the light will remain on and the DTC will remain in memory until the ignition is shut off, or the problem no longer exists.

The DTC is also sent to a "history" file where it will remain until it is manually cleared with an ABS scan tool capable of accessing the history file. An ABS technician that is knowledgeable, and has the proper scan tool, can access the history file and retrieve the DTC. Next time the light comes on, have a technician check it, but DON'T turn the ignition off.