MBman

Hey Gang
Have not been around in awhile cause all was going good until todays haul
Coming down the road the ABS and Brake light came on. Brakes were fine able to stop without problem
Turned her off and lookes at relays, plugged and uplugged them, started her back up and the lights went off
I am still leary and I doubt the relay plug unplug could have done anything.
Any ideas or things I can check before I take her to the ***********
I gotta haul again soon
Thanks'
Ron

Mopardan

If it also gets to the point where your speedo won't work till you get to about 20 mph, I would check the speed sensor on the rear axle.

torquefan

That's the first place I usually look too. Although, if the truck's older than 98, the speedo doesn't use the sensor on the rear axle. Anyway, unplug it, check the connection, hose it out with electronic cleaner, put a dab of dielectric grease on it and put it back together. Follow its wiring up to the frame looking for damage, and you will find another connector there where the sensor harness attaches to the body harness. Give that connector the same treatment, and hopefully that's all it takes.
You can check the sensor's resistance, I can't remember the spec- somewhere between 1000-2000 ohms. If the problem's intermittent, it probably won't show up as bad anyway. If the above doesn't fix it, you can retrieve codes from the system, if I remember you have to ground a wire at the diagnostic connector.

billv45

Also check for vacuum leaks. I had an intermittent leak on mine turning on my lights. The 4-way connector by the master cylinder seemed to be a tad too small for two of the vacuum hoses hooked up to it and it would leak when it swayed forward (best I can figure.) Easy check just shut the engine down and wiggle the hoses around and listen for leaks. Then disconect one of the hose and you should hear the vacuum whish. If it's not there, you've got a leak. Hook up a Mighty Vac to each of the lines to find out which one is the culprit.

MBman

OK mine is a 97 so it looks like the speedo sensor is not present correct?
I will check for the vacuum leak. Is this 4 way connected to the master cylinder???

Could a relay be bad or fuse?

What are the dangers since this is intermtant and I need to still drive it?

chop342

You have no danger to still drive it, the electronic systems used on that truck for the ABS and brake controller are kinda odd. Sounds to me like the rear diff sensor is having issues also check the output shaft speed sensor on the overdrive housing of the trans. check your connections and it wouldn't hurt to remove both of them and clean the crap off the ends, if you have sludge or shaving on the ends it interrupts the magnetic field and will set a code and turn on the lights. Back to the driving issue as long as you have brakes you are safe to drive, the ABS light just means that you have an ABS failure somewhere and if one of your sensors goes open intermitent than it will turn on the BRAKE light. So long as you don't have a mechanical failure of the brake system you will be fine to drive. If the pedal feels good then keep on trucking.a

Chris

MBman

thanks, so there are sensors on each wheel? if so where?

where do I find the diff sensor - top/side?

output sensor on housing of tranny - got that

thanks again

MBman

here is the deal now, my 4 Wheel drive light has come on and is staying on along with the ABS and brake light. I am not in 4W drive and the brakes still work fine
SOunds electrical but I checked and cleaned every connection (I think) and no help
ANy ideas appreciated , if vacuum related, how do I check and where do I start

MBman

Any Ideas - Help
This one is about to drive me crazy

torquefan

I would start now by unplugging the connector from the switch for the 4WD light. It is on the front axle at the disconnect housing. This will tell you whether it is a wiring/cluster problem or if the problem exists in the switch or 4WD mechanical components. With a helper, also take note if the front driveshaft turns when driving while shifted into 2WD.

MBman

figured out the 4 wheel drive light, while spraying the switch with contact cleaner I must have got too much in it and it took awhile to dry out

the other lights are still on can I selectively unplug things to see if they go out?, where would I start?

torquefan

At this time, I would try unplugging the RWAL controller for a minute then plugging it back in. Some faults will only last a split second, but will leave the lights on until manually erased. I really can't remember where the controller is on a 97. Sorry.

I forgot to tell you earlier- make sure your brake lights are working. If they stop, it can set a code.

MBman

OK I replaced the rear sensor on the diferential and still have the lights
Do I have to reset somehow, other sensors involved???

What is the RWAL controller and where do I find it??? on the 97

fschiola

I don't know if you've found your answer but I think that you need to replace the stoplight switch. It contains 3 circuits, one for the cruise control , one for the ABS and the third of course for the stops lights. They can fail separately. They run around $12.00 from Auto Zone.

Stamey

My 96 does this now and then. Lights come on and stay on, usually until th eignition is turned off. When I start it back up th elights are off until whatever triggers it again. Been like that for a year now, and I have never tracked it down. I will be watching the ideas and solutions here so maybe I will finally get off my butt and check it out.

Thanks,
Chris