there is only one problem with the truck
before you say i should have test drove it i did i drove it for abotu 4 miles or so before i put the cash down fro it
my abs and park brake light randomly come one about 3 miles into driveing it some times longer
i have read that it is a speed sensor
my truck is an 01 2500 hd crew cab 4x4 short box with 4 wheel disc brakes and tow haul mode o nthe shifter lever
so any ideas on how much doe its gonna take to get a new sensors
i will be running on a scanner at work monday to determine which one(s) are bad
the truck does not have teh original rims and tires the rims are 16 inch but the tires are 265 75 16 could that also have something to do with the lights

 

Check to see if all of the tires are the same ... different size tires can throw off the ABS system.

Here's where I would start. Firstly, make sure that your braking system equalizes - do both your front and rear brakes get equal hydraulic pressure. Pascal's law says you should have equal pressure at all points in your braking system, as long as it is a sealed system. A way to test this, is to drive the truck about 30 mph, let go of the steering wheel and smash the brakes good and hard. If it jumps to one side or the other, then you have unequal braking, and a hydraulic/caliper/hose/master cylinder issue. A weak brake hose can cause unequal braking, a bad seal at the calipers, etc. This can cause the red brake warning light to come on.

Second, get a scan tool and do one of two things. Drive the truck while looking at the ABS module's data stream and look at your ABS sensors - they should all show you the MPH they're reading. If one drops out, or is popping in and out, or reads differently from the other sensors, then you most likely have an ABS sensor issue. That's one way to test these sensors. Next is to get out your volt meter, and unplug a sensor. Plug your volt meter's leads to the sensor's connector, and spin the wheel. Your ABS sensor should put out Alternating Current - Set your volt meter to read AC voltage! You should have a steady increase in voltage as you spin your wheel faster.

You can also drop the truck into 4x4 and hoist it up so the wheels are off of the ground (BE CAREFUL!), put the truck into drive and let the wheels spin. Look at your scanner, and try to guestimate if each sensor is reading inaccurately.

The ABS module watches each wheel's speed input, and can do one of two things to that hydraulic circuit. It can either add hydraulic pressure, or bleed off hydraulic pressure. It bases what it wants to do on the info it gets from the wheel speed sensors. The ABS module looks for a change in wheel speed that doesn't match the rest. This can turn on the ABS light (And sometimes, when the ABS light is on, the other comes on too)

For example, if you're trying to stop on black ice, and only one wheel starts to slip, the module will block off the pressure going to the caliper, and try to get that wheel to speed up - to grip - again. Having a wheel locked up while trying to stop, is not the safest/best way to stop. The ABS module will try to keep all of the wheels decelerating at the same rate.

I suspect you have mismatching tires, or a bad wheel speed sensor. Hopefully you found my Brakes 101 novel interesting.

Question: Does the ABS pump kick on (Like you're sliding on ice and you hear that buzzing/whirling sound) when your ABS light is on, and when you're stopping? Do you ever hear the ABS pump kick on when you're stopping normally? Does your ABS work when you try to slide on gravel/dirt/snow/ice?

Check out the codes stored in the ABS module.

 

My 2001 GMC 2500HD that I used to have had the same situation. It was a ABS sensor which is part of the hub. I never replaced it - figured I would wait for the bearing in the hub to need replacing and it never did. It would come on at random and seemed to be more frequent in rainy weather. It never affected the way the truck stopped so I just lived with it. I drove it for 2 years like that and then sold the truck (wish I never did) and as far as I know the new owner never has replaced it either.

 

Thanks everyone thats some good info i will probably be replaceing the hub that is bad it does brake evenly when i let go of the wheel that is one of the first things i did to rule out bad brakes i did check the hydrolic brake fluid level as well its at max where it should be ill keep ya posted on what i find out oh and the truck did have a plow and sander in the back from the previous owner but was taken out so i know that the 4x4 was used alot for plowing another reason im leaning towards the sensors being bad

 

Well if it was a plow truck, then the previous owner could have possibly disabled the ABS system. I can't remember the reason for it, but I was talking to someone who had a plow truck and they said it caused all kinds of issues when trying to plow. I wish I could remember what they said about it though ...

I've had ABS sensor wires get chafed by rubbing on the CV axle on a van before. So the ABS would quit when the wires got wet (this was actually shorting the two together). The wheel bearing was bad anyways ... so it got fixed with no problems after that.

 

well none of the wires are disconected or frayed or chafed so ill keep looking into it so far it hasnet affected the braking ability also today i noticed one of our work trucks does the same thing only its a 2wd 2500 no hd just 2500 but hopefully tomorrow i can get it into our shop at work and take a look its gonna be a slow day with us getting snow and sleet and then freezing in the morning

 

Try testing each wheel speed sensor with your AC volt meter.

 

well took the truck into our shop today hooked up to the obd2 scanner and there were no present abs codes so i went to history codes
and bam there was like 3 or 4 codes that started with ebcm electronic brake control modual
so i cleared them and jsut before i left not even 2 blocks away the lights came on again so im gonna pull the truck in tomorrow again and look at it again
adn this time i might drive the truck and use the scanner to see what code it is and i will test the sensors also when i get a chance this weekend