Brake Manual

[Halgar]

Anybody got a link to info or online manual of the brake system for an 02 GMC 1/2 ton truck? I've got an intermittent problem with the ABS and Brake warning lights coming on. I asked the shop what they'd charge to hook up their scanner and they want $200 for an inspection.

Symptoms are the lights come on while driving then seem to reset when the key is turned off. Fire it up and a little while later the lights will come on again. Sometimes it does it at start up, most of the time it's after driving for a while - a mile or more. There seems to be no correlation between this and the weather or driving conditions. This has been coming and going for about the last year. It happens for a week or two then is gone for a month or two.

I got to thinking recently that this may be an "new and improved" early wear warning for the brake pad wear rather than the old scrappers that would squeal before the rivets and pad backers ate the rotors. The truck has 65K miles on it and the brakes have never been touched, other than visual inspections by me periodically.

I plan to do an inspection this weekend, and it would be nice to know the locations of the various sensors and electrical components and connections. If it isn't pad wear, which seems doubtful, I'm hoping it's just a bad connection somewhere.

[Charlie don't surf]

Pad wear should have a different sensor and idiot light that will look look like this (o) but there is an exclamation point in the circle.

The truck has at least 4 wheel speed sensors that it uses to gather data to determine the actuation of brake pulses during etc etc etc. If a sensor is bad, the abs light comes on, if it has a fault code, the abs light comes on. Keep in mind that the ABS system is deactivated when the light is on.

If it is intermit then-

1) There is an obstruction on the sensor face ( most common is rust belt areas )

2) There is a nick in the wire running connection to the sensor ( not uncommon with road debris)

3) There is corrosion at the connector ( same as #1 )


I would pull each wheel off, locate the sensors and do a visual on the wires and connectors-then clean the contacts and coat with dielectric grease- then see what happens.

I don't know what state you are in, but unless they charge 2 bills per hr, they can't bang you 2 bills for a diagnostic. And the DTC's that show will be

1) brake fault-incorrect wheel speed

2) brake fault-abs

3) wheel speed sensor fault

And then they have to do what I just told you above-

[Halgar]

Thanks for the technicals Reg, as far as the inspection, that was the plan, pull the wheels and work my way up under the hood. Interesting info about the ABS not functioning when the light is on. To be honest, there has not been one inkling that there's a problem, other than the lights on. When I asked the shop about it they said it was likely a loose connection, if that was the case the price would be $200ish, if it was the computer it would be over $1200. Money being what it is these days, it warrants me having a look for myself first.

I'm not getting that particular idiot light, just the ABS light and the "brake" light as if the parking brake were on.

There's also a red stick figure that flashes incessantly, what the heck is THAT all about?

[Charlie don't surf]

Here is the easy "computer" test-

when all the lights are on, ( and when it's safe ) do a panic stop- if you hear or feel the ABS chatter , it working-then you may have a computer fault ( or the dash unit is bad )

[Charlie don't surf]

Oh, I assume that you have checked the Brake fluid level as well

[Halgar]

I have just the yard for that test. Oh wait, you said stomp the brakes, not Oakie dyno test ...

Brake fluid? What's that?!?!? That's the nice thing about an plastic reservoir, you can see the level and it looks fine.

[Lowgear]

If you bring it to an auto parts chain store don't they plug in the code reader for free?

[badhoopty]

If you bring it to an auto parts chain store don't they plug in the code reader for free?

was gonna say the same thing. they can at least pull the codes for you. autozone i know will do it.

i'm sure abs is good, but i've had a couple times in my firebird where i've had to stop fast enough for it to kick in and i do NOT like the feeling of it.

[SoloGraphix]

The ABS in the Suzuki X-90 I had was the most god awful experience I have ever encountered. When it felt the wheel slip it pretty much shuddered a few times then just let the brakes loose for a second, which is an extremely fun experience while traveling downhill in snow. It caught me off guard twice, and both times almost resulted in ugly outcomes. I started going down hill in snow using the E-Brake mostly and dragging the foot pedal.

[fastang]

Friend has the same problem. I don't remember exactly , I will ask him tonight, but I think its the wheel speed sensor went tits up and cost about $200 to replace. I guess it will not affact the ABS function at all.

I will get bact to you/

Mike

[Halgar]

I've thought about calling a few parts stores and seeing if they'd do it, but most of the places around here don't exactly instill confidence that they're able to give me the right parts, let alone let them touch my truck. It's an option that I'll keep open, but I'd rather do a little sleuthing myself first.

I don't know that I've ever engaged the ABS on this truck. I did it a few times in my '95 though, one time in particular was quite the pucker event. Coasting down a freeway offramp with a fully loaded 6x12 dump trailer full of dirt when all of a sudden traffic was at a stand still. Lay the brakes to the floor, all I get is ABS chatter, no stopping - silly me, I'd forgotten to adjust the trailer brakes after loading ... I reach down and flip the trailer brake module to full on, stopping the whole mess in less than 50 feet! Who'd have thought that a fully loaded trailer could lock it's brakes? That was the first and the last time I ever forgot to adjust the brakes on the trailer! LOL

Friend has the same problem. I don't remember exactly , I will ask him tonight, but I think its the wheel speed sensor went tits up and cost about $200 to replace. I guess it will not affact the ABS function at all.

I will get bact to you/

Mike

Thanks for that, if this is the problem in my case, I wonder how one goes about testing the sensors.

[fastang]

I don't remember how they found the problem. The guy cleared the trouble code but it came back a day or so later. He did say it won't have any effect on the ABS working or not. This may not be your problem so take it for what its worth.