This just started last Thursday.
Driving along......straight stretch of road at ~50 mph, not hitting the brakes...and the ABS/Brake lights pop on.

Test the brakes, all seems OK, (Truck stops same as always).
Got home, turned off truck, restarted, lights not on.

Decided to change the Rear Wheel Speed Sensor.

Drove to work the next day, light off , 10 minutes into the trip......same thing, both lights on for no reason.

Topped off the fluid level in the reservoir (it was ~1/4" low) and all seemed OK.

Drove to work on Friday, everything peachy, drove home, no warning lights.

Friday afternoon drove from Arlington, Va heading for the daughter's place an hour west of Richmond. Got 2 hrs down the road and Bingo, lights popped on.

I shut the truck down, lights went off and stayed off for ~ 1/2 hr before coming back on.

Drove home this AM........got 2 1/2 hrs up the road before the lights came on.
Is my truck possessed?


PS: '99s don't have the key on-off feature to "read" the codes.
4 wheel ABS system.

 

try cleaning your sensors at the hubs. the sensors get dirty there. i know i have to clean them monthly! in the fron you can trace the extra wire that runs along the brake line! in the rear i wouldnt know. i just hit it with my pressure washer when my truck gets a bath.

 

I'll check them tonight.

Thanks........

 

I got back under the truck tonight to readjust my (new) rear brakes, and bleed the brake system of all that oooooooold 1999 brake fluid.

I discovered that the driver's side sway bar link for the rear bar was SEVERELY rubbing on the emergency brake cable AND the harness for the rear Wheel Speed Sensor.
(It had rubbed through the outer harness, and through the insulation on one of the wires exposing the copper conductor, allowing it to periodically short out on the sway bar link)
I think I found my "Mystery" ABS warning light problem.
I slit a piece of fuel line and (after coating the exposed wire with RTV), zip tied it over the wire, secured the E-Brake cable and harness to provide clearance.

If you're under your truck, check out this area for a possible future problem.

 

I've had mine to the shop twice already for similar problem. At a bout 50-60 mph the ABS and Brake warning light come on,but also my speedo jumps around. With these lights on, my brakes work fine. After shutting off truck, lights go out, and my brakes feel weird...like ABS kicking in...keep on feeling weird until ABS light and brake light come on again. Shop put on a new plugin and did some re-wiring to the wheelspeed sensor(also new), but the problem persists. They have no idea...I'll check for rubbing near the emergency cable as well. I did notice alot of old mud caked up in the frame near the sway bar link-or is it a rear wheel ABS link...could be a problem there.

 

Update:
No Brake/ABS warning light activation since this repair.

Looks like that solved the problem.

 

I was under truck today, no bad wires found...only thing odd was dr. side rear spring u-bolts were a bit loose, impact would not tighten, so I figure they'll twist off if I try too hard. Could a bad ABS load sensing lever on the rear left side cause these symptoms? I can't tell if it's good or bad...that area was packed full of dried mud.

 

I thought the magnetic sensors were on the sensor that mounts in the rear diff. housing? I'll have to pull my hubs and look.

 

If you have 4 wheel ABS, there are sensors on each front wheel as well as the rear diff sensor. You should be able to see them by looking under the truck on the inside of each wheel with out pulling anything apart. There will be a wire running to them that aren't found on the non 4W ABS trucks.

 

If your talking about the proportioning valve for the rear brakes by the rear axle, I shouldn't have anything to do with your ABS light being on.

 

I just have the rear wheel ABS, so there's no point in pulling the rear wheels. Is there a possibility the brand new wheel speed sensor is bad?

 

It's possible that the sensor is bad. I replaced mine and had a problem about 6 months later. Thinking it was the sensor, I went back to the dealer and found out that if you have your receipt, the part is warrantied for 12 months. I wasn't bad. Didn't cure my problem but a new stoplight switch did. The only thing that bugs me about your problem is that you have a speedo problem (and it's a 5 speed) and you can feel a difference in the brake performance. I'm almost leaning to tell you to have the ABS scanned but it's expensive. You don't want to take any chances, so go with your own feelings. BTW, the stoplight switch is about $12.00 (US) at Auto Zone. (Also, you have some very nice toys.)

 

where is the stoplight switch located? I searched the factory service manual for "stoplight switch" but it didnt return any results.

 

its under the dash on the brake pedal push the brakes a little and you will hear it.

 

Or follow the brake pedal from the pad up to the pivot point. you will see a white plastic box with a plug with 6 wires coming out of the top facing away from the firewall. It's quite a ways up under the dash.