For the experts/any help will do:

My 1995 Ford Aerostar had it's rear brakes and emergency brake system done by a professional mechanic. About 3 weeks later the ABS and Brake Light came on and are constantly on. I just replace new rotors/pads myself under a mechanics supervisor. I took the van back in to the place that did the rear brakes, and they did a diagnostic test and stated it was the master cyclinder tanks with the sensor. They replaced it at $80.00 and the lights are still on. Needless to say, I didn't pay yet. I am look to find out it since the first time the lights stayed on, is there a chance the computer has to be reset. What other problems could it be. Appreciate all your knowledge and help. Thanks.
Flemm

 

I just looked at my 92, I don't see how the master cylinder sensor could set off the abs light, it's just a fluid level sensor that would turn on the the regular brake warning light. I'll look up your year tommorrow and see if I can't find something for you.

 

Anyone with any answers to this would be great as I have the same problem when I did my brakes... the break lights came on, then the rear abs light came on. so I had a mechanic redue the rear brakes and they still stayed on and sometime the lights alternate when they want to come on ...and sometime they don't come on.

Thanks

 

I just had another thought, did you open the bleeder screw when pushing the piston in the calipers back into the bore? Not doing so sends burnt up nasty brake fluid back up the system and I have heard of that setting off the abs light. Haven't actually seen it myself but if that did happen I would think a good flush of the brake system would solve it.

 

Most likely the speed sensor is going bad on the rear axel housing. You may notice it works at higher ambient temps and humidity. It has one bolt that holds it on, the trick is to be careful with the plug clips, I used toothpicks to spread the clips so I could disconnect the harness. Try fordpartsonline.com to get an idea of a fair price, before heading to your dealer. Takes about 15 minutes to change one out.

 

Thanks guys: To jkorreck's reply. When I put the piston back in the calipers, there was brake fluid that came out the master cyclinder. I got the mechanic at the auto club to look and he said that was absolutely normal when the piston is put back in. The brakes are working fine. It's just that the word is if the ABS Light is on then the sensor is being overridden and really not working like the brakes are suppport to. Alot of people have stated that the sensor in the master cyclinder tank does effect all brakes sensing. The lights were on way before I did the front back. Do you know if it will hurt to take negative off battery and reset the computer. Your help is greatly appreciated and any further info is considered. Flemm

 

On the 94 Aero when I replaced the speed sensor, I never disconnected the battery afterward, and the ABS light went out. So I don't think its going to have any effect on the ABS to unhook the battery. Also I replaced my sensor about a year ago. The speed sensor is $14.66. It is magnetic if I remember correctly, and all magnets loose their power over time.

 

Aftermidnite, could you please tell me exactly where the speed sensor is located on a 93 XLT. I was underneath today and couldnt find anthing resemling one. Also do you know exactly where the ABS control module is and what it looks like. I need to get a propermanual. Thanks.-Andrew.

 

The speed sensor is on the differential housing on the rear axel. If you think of the axel as being a clock and 3 O'clock is on the front of the differential house its about at 1 O'clock. Service manuals do not cover ABS systems. I do not know where the module is. A Dealer was charging the company I worked for a $1000 plus to fix the ABS on our full size vans. I discovered we were only having problems with the Vans that went to Cell sites. (mud) A $4.00 can of electrical parts cleaner would fix 90% of them, by cleaning the connector plug. A new speed sensor took care of the rest.

 

I had this problem on my wife's van & found a simple free fix. Problem is I can't seem to find the instructions I followed right now. I will get back with something after work TODAY.

 

Hey Guys: Thanks for all your info. Problem still exists. Both lights still on. I followed the manual and talked with a buddy. I disconnected the plug to the RABS Module and connected a ground wire to the black/orange leed to try and get a reading via the flash/dash method. The ABS light went out but not the brake light when disconnected. Could not get a code reading. Connected plug back to module and light back on. I will wait a bit long for more input but looks like might have to go back to dealer.

 

I think your remaining red light is a problem with the pressure differential switch within the master cylinder. Your '95 is a different configuration than my '91 but I believe if you look on the side of the master cylinder, you will find a two-wire connector. (On edit: your switch may be on a remote valve assembly - see reference artcle below) Remove this and put a jumper wire across the connector you pulled off. Start the van and see if the red light goes out. If so, the internal switch is grounded. This often happens when fluid flow is reversed within the master cylinder. (i.e. compressing caliper pistons) Sometimes re-bleeding the brakes will restore the function. Other times, it will reset itself after driving around awhile. I would leave the jumper in place and just drive it, then re-connect after one week and see what happens.

On edit: Here is an excellent article to help you sort out these brake warning lights. http://www.babcox.com/editorial/bf/bf69936.htm

 

That is a GREAT article.
The "Brake Combination Valve is right below the master Cyl.
I just unplugged the switch in the top middle .
Unscrewed the switch.
You are looking at a short rod/plunger.
Take that out & clean it and the hole it came out of. (I used needle nose pliers to pull it.)
Put it all back together & you should be fixed.
Easy job...10 Min.
You don't break the system open so no bleeding needed.

 

To all (especially aerocolorado and leader): aero thanks for that website. Very informative. For Leader, thanks for explaining that valve. On my 95 aerostar the value is on a part below the master cylinder which I believe provides brake fluid to the rear of the vehicle. Anyway, on this part there is a plug connect to it. I disconnected the plug and took pliers to unscrew the black female part. When I got it off, there was the plunger value. Both the value and the hole had a bunch of hard corroded (I think brake fluid). I cleaned the value, used air compressor to blow out the gunk in the hole. Put it back together - lights out. But guess what, when I put the part back on, I tighten to tight and broke it. Now can I somehow get that piece out. I think it's all one part which means I will have to take it off, put the brake lines back on and then bleed them. Would that make since to you. Please let me know as the part is gun-taped right now. Thanks again. Flemm

 

Hummmm...... Plastic isn't as strong as steel. Did I forget to mention that ?
First I would try to get the broken part out (small screw driver or pick of somekind) If you can get it out get another one from a junk yard & you're back in bus.
If not... Yup you will have to replace the whole valve and bleed the system.
Glad you got the lights out. Sorry you broke it.