94 Jeep Grand Cherokee - Anytime I slow down (fast or slow) - right about the 5mp hour mark the abs kicks in (pulsating brake pedal) no matter what type of surface I'm on. I replaced the ABS Controller but that didn't fix it. The ABS light on the dashboard is NOT on. Any ideas how to start diagnosing this problem?

Thanks
John

 

It seems if there were a problem the ABS light would be on. I'm not implying you don't know your vehicle, but are you sure it's not warped rotors?
And Welcome to CF.

 

Wheel speed sensors can cause a problem like that. Take them off and clean them or replace them.

 

Wouldn't that activate the ABS light though?

 

I would think so, but i have had a similar problem on my XJ. I guess if it is sending a signal that is not correct, but still sending a signal, there would be a chance that the light would not come on. Kind of like a bad O2 sensor that doesn't set a CEL.
Not sure though, Just a thought.

 

Yeah I'm sure. This is the very definitive ABS pulsation and it only occurs at the 5mp mark. I've had warped rotors on my other vehicle and know what your talking about - that vibration... but this is different.

I'll check into the speed sensors unless any one has any other ideas...

Thanks
John

 

Mine had the same problem, the module(i thin k thats the name computer under the abs valve) went bad and caused it to do that. My abs light was on, I just took all the fuses out for the abs. Yours may have the relay and I took the bulb out of the dash.

 

So if I read this right, your solution was to basically disable the ABS correct?

 

Have you cleaned/replaced the wheel speed sensors yet?

 

Not yet - it's not exactly cheap to replace all 4 sensors to just hope that fixes the problem. From my limited resaerch it seems you can test the sensors with an ohm meter. So might dig further into that this weekend.

John

 

Car maintenence is never cheap, neither is malfunctioning brakes...

It is however extremely cheap to clean your sensors, by a can of brake cleaner (2.99) and clean them. I have to do this once every few years on my XJ.

You can check the resistance of the sensors, but i do not remember the specs for testing.

 

I understand the cost of vehicle maintenance - but I just want to make sure I'm spending my money correctly. I've learned my lesson on just replacing parts "in hopes" that it fixes the problem... usually (in my experience) it isn't the problem.

a little more info on the problem I just found out... this was my dad jeep before he gave it to me - with this problem - he's lived with it for years. He told me it started happening after they had the brakes done at some shop - who after several times of bringing the turck back to them said "they couldn't fix it" - which I'm sure means "we don't want to admit we broke it and pay to fix it". Anyway - nothing I can do about that but... does that information help at all in a diagnosis? Still seems pretty likely it is a wheel speed sensor that has been damaged...

guess I'll start with cleaning and inspecting the sensors - seems like a cheap place to start.... now i gotta figure out where they are... (this is my 1st jeep)

 

Find a write-up on what the resistance should be and check that first.

As far as getting to the sensors, take the wheel off and then the brake caliper and rotor, you should see it from there. it could be that the shop messed up a sensor, if so, its likely they could have messed up one of the front sensors.

 

I had the same problem on my XJ. It was my speed sensor. It had gotten bumped and wasn't quite on the tone ring. I just loosened it and readjusted it. Problem Solved and no $$$...