John H

Hi everyone, Just bought a 93 D250 CTD. When I slow down at a stop light, both the ABS and the Brake warning lights come on together. When the engine revs pick back up on setting off again, they both go out. I seem to recall that on the first gen trucks, when both lights come on, it is significant but I've forgotten why. I've tried doing a search, but it comes up empty. Can anyone point me in the right direction? ???<br><br>John H

Monty

First of all. Check your brake fluid and make sure it is at the full level. Could be low vacuum, there are three switches connected to the brake warning lamp; parking brake, pressure differential switch, and low brake booster vacuum. The low vacuum switch is activated if the vacuum falls below 8.5 inches for more than 10 seconds. As the vacuum pump is engine driven, I would suspect this could be the problem. Hopefully it would only be a leak and not the pump giving out.<br>The antilock lamp is another matter, which from consulting the manual, could be for numerous reasons, you would have to retrieve the fault code to be able to identify the problem, but however fault #11 has to do with the brake pedal swith, and if you are having a vacuum problem, the pedal may be droping slightly and tripping the switch. <br><br> To run a diagnostic fault code check: Pull the glove box out and behind it you will see a box with a bunch of wires running to it. Follow those wires back about an inch or so and you will find a wire with a plug on the end. I think it's a black wire. Anyway, ground that wire for a second and watch your brake warning lite. It will blink a code. Count all of the flashes, include the long one, the codes are numbered 1-15. The antilock controller can only hold one code at a time, so the suggested procedure is to fix the code, clear by disconnecting the control for 30 seconds and then test drive and check for more codes. Usually #9 code seems to be the one that comes up the most. 9= Speed sensor wiring/resistance (usually high reading). The sensor is located on the rear end.<br><br><br><br><br>

Bob Beauchaine

I had the same problem a couple of months ago and after fooling around with my truck I finally adjusted the rear brakes - problem sloved. My braking felt pretty good so I wasn't too worried about the light. BTW I also found one of the adjusters disconnected - don't know why. ;D
Bob

John H

Thanks, I was hoping it might be something simple, but I guess it never works out that way. Since it is going to go below freezing tonight, and the days are'nt going to be much better, it may take me a while before I can check everything out, but I will let you know what happens.<br><br>John H

John H

I just re-read what I'd posted, and it looked like I tried to fix the problem by throwing lots of parts at it. In my own defence, what I actually did was to fix other brake problems along the way, and just kept looking to see if the light problem was fixed as well.
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I wanted to finish off this thread, since I hate not to post a conclusion. Also, I have recently seen other people having similar problems, and I thought it might help.
This has taken a while to solve, since I have had other more important problems to address along the way.
Briefly, after completely renewing the brakes, including changing both front brake calipers, new pads, rotors, rear shoes, and finally ABS module and sensor, which still didn't fix the lights, I found time to do some trouble shooting. The real problem was as mentioned in one of the replies to my original question. After sitting at idle for a while, I found the boost vacuum fell below 8.5&quot;, which then turned on the ABS and brake warning lights. The problem was caused by a faulty brake power booster, which couldn't hold vacuum. I changed that, and the problem went away. Thanks to the people who responded.

John

TexasBlake

Mine came on because I had a leaky brake booster. Could hear a hiss at my brake pedal.