I am having trouble with the abs braking system on a 1998 chevy blazer. The yellow brake light is usually off for the first few minutes of driving and then comes on and stays on until the car is turned off. The abs brakes pulse and make a noise and seem to try to work even when touching the brakes lightly. It has 170,000 miles.

The brake sensors. Cars with antilock brakes have an amber or yellow warning light, which usually says ABS. If this light stays illuminated after the bulb check, it indicates a problem with the antilock braking system. The ABS controller will disable the system and your brakes should function as if you don't have ABS. In this case, you can safely drive the car to a mechanic for service.

I think I would get the body computer scanned for trouble codes and find out why the ABS warning light is on first.
The hissing noise usually means the booster is leaking vac but if the booster was faulty the brake pedal would be hard to push.

Have the charging system tested when this happens, you could have a defective diode in the alternator.

Have you not had the vehicle diagnosed
to find the cause of the problem?

Not safe to use like it is

No one can tell you what is wrong with it.
That is a job for an experienced mechanic

Obviously you have a Failed ABS System issue

The light indicates that there is a fault in your Anti-Lock Brake System. Your primary braking system will still work, but you have likely lost the the extra protection of the ABS which prevents, or at least greatly reduces, the chance of entering a dangerous skid when brakes are applied on wet, icy, or otherwise slippery pavement. The ABS system should only be worked on by a qualified mechanic, and for your own safety you should have the vehicle's OBD computer scanned and necessary repairs taken care of as soon as possible.

SOUND LIKE PROBLEM IN THE ABS BRAKE SYSTEM AND TRAC SYSTEM.TAKE VECHICLE TO DEALERSHIP.THEY HAVE TO USE A TECH SCANNER TO TROUBLE SHOOT AND FIX PROBLEM.

hey did you ever figure out what the problem was, i have a chevy blazer with the same symptoms...need to know if its worth the money to fix.

yes its at the rear of trans

Drive it. Then have the rear abs brake sensors checked because they seem to be the first to go in a system like that. Someone with a scan tool should be able to read out any trouble codes in the abs system

When the ABS light is on when driving there is a problem in the anti lock brake system and you will need to have it tested to find out what the problem is. As long as the light is on the ABS has been shut off by the computer until it is repaired. There could be problems with one of the wheel speed sensors, wiring or the ABS pump. On some vehicles the red brake light will come on too.