I've got an ABS light and the parking brake light on whenever I drive my truck and the speedometer goes nuts too. It will be steady at say, 70 MPH, then it will jump to 90, then down to 55, etc. so I really have no idea how fast I'm going. Is this some kind of speed sensor issue? I replaced the little sensor on top of the rear axle last September when I had those two lights on and they went away until about a week ago and now they are back but with the added pleasure of a wacky speedometer. Please help and I thank you in advance.

 

Have a look at the back of your transfer case, on the output shaft. Is there a sensor there? If there is, replace it. If there isn't, then the year old sensor in the diff has failed again.

 

his is probbaly on the diff because i think in 97 or 98 they switched to the one on the diff being the speed sensor and the abs sensor also

 

yup I would be willing to bet thats its the vss (vehicle speed sensor) on your rear diff.... there's been a few here lately with this exact same problem....

 

I had the exact problem today. Just replaced the vehicle speed sensor on the rear diff and everything went back to normal. its an easy fix but cost me $44

 

Thanks, guys. I'll look into that.

 

Well, I replaced that sensor but that did not fix the problem. The ABS and parking brake lights still come on and I get a "pulsing" in the brake pedal for a second or two before the lights come on every time I drive the truck now. For example, I'll be driving back home to NM from Oklahoma and I'll have to stop for gas so I kill the truck. When I start it, the ABS and brake lights are off until I start driving and have to use the brakes. Once I press the brake pedal, it pulses like the ABS is engaging and then those two lights come on again about 10 seconds later but there is no more pulsing in the pedal after that.

Also, the speedometer is fine unless I hit rough pavement on the interstate. I-40 Eastbound into Oklahoma City is a damn good example if you are familiar with the area. That has got to be the roughest stretch of interstate in the lower 48 and the speedometer swings wildly from about 50-90 MPH even though I'm doing a constant 70 or so.

Any more ideas as to what the problem could be? I'm a little nervous now that I'm getting the pulsing in the brake pedal before the lights come on. All I need is a brake system failure when driving on the interstate.

 

Ttt ttt

 

pop the hood and see if there is brake fluid in it? Maybe bad rear wheel cylinders

 

The pulsing in your pedal, that stops when the lights come on, is probably the antilock brakes engaging, when they get a funky signal from the speed sensor. The fact that your speedo exhibits odd behavior when you go over bumps tells me something else is going on there.

The reason that it stops when the lights come on is...... when you first use your brakes, the lights come on because the computer is seeing a problem, once it sees a problem, it disables the antilock portion of your brake system, thus, no more pedal pulsation.

Do you have RWAL, or 4WAL?