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Anti-lock brakes

I everyone I’m new here. I have a question about anti-lock brakes. I have a 93 Grand marquis. It only has a little over 31 thousand miles. About 2 years ago the yellow anti-lock brake warning light started going off every now and again. We took it to someone who ran a diagnostic test with a computer and they said all they could tell is something wasn’t working right with the system. They said it could cost 900 to fix and it would be a used part so it might not work. Any way some times when we are driving there is a small short stop and shaking, kind of a grinding noise and then the yellow light goes on. The guy said that it was just the anti-brakes switching over to the regular braking system. Does any one know if this is normal? Or could this be dangerous?

The brakes activating on their own while driving, due to a fault in the ABS system? Certainly this is dangerous. Very.

Edit, actually it is the traction control that can turn on the brakes… Same mechanics, different software function. thanks TSM.

It is dangerous. You need someone with ability to read ABS codes off your system and diagnose the problem properly. The fix might be more than what the car is worth, but still probably only 2-3 payments on a new car, so your call.

“We took it to someone who ran a diagnostic test with a computer and they said all they could tell is something wasn’t working right”

This isn’t a diagnosis. This is someone either without the proper knowledge or too lazy to diagnose the problem. Their estimate is meaningless, because they had zero idea what they were talking about. It’s just as well that they didn’t do anything.

You need a competent technician to look at your brakes NOW… without further ado. There are a number of possibilities regarding the grinding and shaking… none of which will fix themselves, all of which can be diagnosed by a competent shop, and some of which could be downright dangerous.

ABS (not to be confused with stability control) will not cause a brake to engage itself. It can only interfere with the engagement of a brake. Simplified, it monitors the speed of each wheel, and when it detects one not turning while the others still are, it assumes that tire is skidding and activates a valve in its specific brake line to interfere with that brake’s hydraulic line in a pulsating fashion. It does this by sending a “square wave” to the valve’s solenoid, causing it to rapidly open and close.

Bottom line: get this to a qualified independently owned and operated shop of good reputation IMMEDIATELY. Get it properly diagnosed and repaired.

Agree with the rest here. If parts aren’t available to repair it, you might consider having the fuse plugged. The ABS light will stay on but the system won’t actuate.

Thanks everyone for your advice, we will call a shop tomorrow. I’ll let everyone know what they said. God bless.

If it were my car I’d just disconnect the ABS by pulling the fuse or whatever. I’m not saying that is necessarily safe, just that’s what I’d do. Beyond that, my first suspicion would by a faulty wheel speed sensor. Those operate in a tough environment, and it could be something as simple as a corroded connector.

A 1993 model uses OBD I diagnostic system, and most shops are tooled up and experienced for cars equipped with the OBD II system. That’s just the problem with driving older cars, finding someone experienced and knowledgeable enough to work on them. I’d avoid the first shop’s suggestion, as it doesn’t seem to based on a thorough, experienced diagnosis. OP might do a little research and see if there’s an inde shop in the vicinity that specializes in older cars like this, especially cars of this make. I’ll bet there is, but it may take a good deal of effort to find them.

The most common cause of ABS issue is the ABS wheel sensors or the reluctor that is built into the hub or axle. Sometimes the sensors “nose” is full of rust and it cannot detect the spinning wheel…and when it cannot detect it…it assumes that wheel is locked up.

Rust and other crap often times clogs up the sensors “view” of the wheels rotation. The axle or wheel has a notched wheel that rotates…the sensore detects the peaks and valleys of this wheel to know the rotational speed or if it is locked up… Most times these wheels are cut into the axle shaft or other steel hub material…

In the case of one Jaguar I repaired…they installed a separate steel ring onto the end of an axle…this ring rusts and falls off…triggering the ABS light with no hope of turning it off until that reluctor wheel piece of steel was reinstalled… In FACT that Jaguar was nothing but a glorified Ford Taurus…so Ford may have installed another one of those snap on reluctor wheels onto this vehicles wheels or hubs as well… Hmmm

I would be looking hard at the sensors at all 4 corners…and…making sure there is no rust or gunk obscuring the sensors “view” of the reluctor wheel…could be a simple case of sensor “Blindness” or the sensor has no peaks and valleys to look at because the ring fell off… Usually these things are cut into the steel…but ever since that removable ring…I never forgot about it…