Flakb8t

My 95 3/4 ton with 68k is making me crazy. The ABS light and brake light are on and the tranny has some funny shift points until you hit overdrive and then it is fine. There is plenty of fluid in the master cylinder, the brakes seem to work fine, and plenty of fluid in the tranny. I don't think the tranny filter has ever been changed though. I checked some of the obvious vacum hoses that were mentioned earlyer posts and looked at the main fuse block under the hood. I really did not find much. I made sure the rear speed sensor in the top of the diff had a good clean connection. I even pulled the sensor out and cleaned it. ABS and brake light is still on. A buddy of mine turned the key off and on 3 times and the check engine light flashed 5 times, twice. He said the code it flashed was "55". Other than the weird shift points and abs/brake light being on the truck runs great.

There was lots of info on this great web site about my problem but I got overwhelmed with possible fixes. What you be the next logical steps to follow? Thanks for any help.

Greg
95 2500 2wd

somis13

once the code is stored from a bad speed sensor the lite will come on even though you replaced the part. You may have to stop by a chrysler dealer to have the code cleared. thats what mine was doing. and I had to do that.sorry, I cant help you with the shifting trouble

Flakb8t

Thanks for the info. I'll try anything at this point.

kevellis32

my abs and brake light are on as well. I work at a dealership with a dodge drb so i was able to check the code there, but it said i needed a new ABS sensor, which runs close to 500$ at my cost, so i will just let the light stay on for now. If you can't get that light to turn off, that may be the same problem you are having.

paco72

check out the vacuum switch. under hood drivers side under the abs stuff. use a vacuum pump or jumper out.the codes can be erased by disconnecting the pcm. passenger side firewall. you have to have abunch of engine starts to have the codes go away without unplugging pcm, if problem is fixed. otherwise they just keep on. hope this helps.
frank

Flakb8t

Well, I installed a new rear speed sensor in hopes that it would be a cheap fix. But, I still have the ABS and brake light on. And, I do not have any ABS (tired a hard stop on a country road and slid to a stop). As to the PCM is it reachable from under the hood or do i have to take apart the passenger side of the dash? Also, the vacum switch. I looked around under the hood around the master cylinder and really did not see it. Is it part of the MS or is it a component by itself?

Thanks again for all the help.

Go Sooners

paco72

if the country road is dirt or clay, it might feel like a slide. did you feel any pulsation in the pedal? the PCM is located behind the air filter box. you should be able to clear codes by disconnecting all 4 cables from the batteries. the code 55 means the search for trouble codes is complete. thats all. the vacuum switch is located on the drivers side inner fender just below hood hinge. the switch is mounted under the ABS module. it has a vacuum line and a wiring harness to it. a real PITA to replace. switch is dealer item. you may have to go down and show them what you are talking about. call and check price. I assume that you have checked fuses and relays, proportioning valve and all of that?



once again, good luck. frank

Flakb8t

If the rear speed sensor was bad and I have replaced it with a new one will the ABS/brake light up and the ABS system still fail to operate until the error codes have been cleared out of the PCM? And If I understand correctly, I have to disconnect all four battery cables to do this? I'm going to take a good look at it this weekend.

Thanks again for all the help. I'm sure that I can track down the problem with everyones help.

gmctd

Did you check vacuum at the VAC Switch on the wheel well over by the drivers-side hood hinges?

Gotta be ~25"HG to shut off the ABS\Brake lites - or, the switch is bad - pull the plug and short the two wires together with a paperclip - lites'll go away

paco72

the error codes will not cause the ABS system to malfunction! put the error codes aside for now. look for the vacuum switch. determine if you have at least ~25" of vacuum at the switch. if you do. then disconnect the plug at the switch, then short the 2 wires in the plug from the wiring harness with a bent paper clip, like gmctd. said. if the lights go out replace the switch. if you do not have ~25" of vacuum, you have a vacuum leak or a failed vac pump.
maybe your bud has a vac guage. I don't remember the price of vac guage kit but it is well worth having handy. frank

Flakb8t

Well, I found the vac switch right where you said it would be. Mine had a 3 prong electrical connection. I shorted out 2 of the 3 and blew a 20amp fuse. Replaced the fuse and noticed that as long as I kept the vac switch disconnected the ABS/brake light would stay off. I also had plenty of vacum to the switch. I don't have a tool for measuring vacum but it seem pretty strong. After removing the vac switch I found that the plastic white stuff under the bracket has a big crack in it. Also, I reconnected the vac line to it (motor running) and checked for continuity and never could get a reading from any of the 3 prongs located inside the vac switch.

So, now I am thinking it must be the vac switch. None of the retail stores have it. I checked with the dealer and he could not find it based on my discription over the phone. I told them it was a vacum switch for the ABS. Should I call it something else? I think I'm getting very close.

gmctd

The crack likely runs thru the sealed vacuum chamber, preventing the diaphragm from actuating the switch.

Time to deal with the Dodge Boys - carry the module in to the parts guy at the dealership, might jog somebody's memory

paco72

hooyah. it sounds like you are on the right track. sorry about fuse. should have warned you about ground. like gmtcd. says take old switch to dealer parts guy. it should have a part # on it. it is best to keep the switch in the system, warning for low vac from pump and to brakes booster. if vac falls below 8.5" for 8 to 10 seconds lights will come on. hope this does it.let us know. frank

Flakb8t

I have not made it to the dealership yet but I was messing around with that vac switch and noticed that it will hold a vacum even with that big crack in it. I thought that something enternal had failed that would prohibit the switches from completing the circuit inside of it. But, today I plugged the electrical connector back into the switch and now the ABS/brake light are off. I pumped the brake pedal several times and the ABS/brake would flash at me and then go off. I'm gonna have to road test it again. If I pull a vacum on that switch and hook my meter up to it, shouldn't I be able to check for continuity?

I did notice that if I pumped the brake pedal and held the pedal with a firm foot, the pedal would ever so slowly sink. Does this mean the MS is going? The mystery continues.

I'll let ya know what the dealer says about the part.

Thanks again.

paco72

gmtcd. please jump in... flak. you could have a leak in the system. a bad wheel cylnd. brake booster, low brake fluid. how did you check vacuum? just curious. you could have worn brake pads or shoes. there is an answer to this mystery in total. some where. just one piece at a time. you may have to get system read by scanner. keep foot off brake pedal when starting truck.
frank