2004 GMC C5500 - Trying To Get ABS Codes

[protraxrptr17]

I know this is a medium duty truck, but it has an OBD II plug. I can enter VIN into my MODIS as a 3500 and get engine/trans codes no problem. This particular truck is my wrecker, but I work on about 6 of these trucks and brake faults are common, so I need to be able to do this. I have tried on another 5500 with no faults and still get the no comm message.

[fortknoxx]

is there a prob with abs or just a light? if all else fails, look on the inside of the rotors see what condition the abs ring is in. My pieces 03 Intnl 4300 the reluctor ring on the inside of the rotors disinigrated. sensors not able to read.

[protraxrptr17]

Well its actually both. It has a hyroboost setup with an emergency electric pump. If there is a fault with that you get the red brake light and the annoying chime. The orange ABS light was on long before that one came on. I just bought this truck about 2 weeks ago, but I have been doing all the work on it since '06. First tried to read it prolly sometime in '08, couldnt get in so I told them to just run it. The chime just started. It has a new booster and it came with a new flow sensor. I swapped the brake pedal switch with one off a truck that has no faults. Those switches suppoedly give alot of problems. Really need some codes so I don't have to do a bunch of trial and error.

[ricmorin]

Do you know anybody with a Tech2? You can get in with that. I've been into many med-duty Chevy's with it.

[protraxrptr17]

I tried one guy, but I'm not convinced he knew what he was doing or that his tool was working right. I may just have to get the dealer to do it for me, but like I said, I have a few customers with these and it doesn't look good when I can't do it myself.

[steven kiser]

there is a pressure switch that will trigger an alarm if there is low hydraulic pressure and will activate the electrical side of the system. during start up the systems (i believe) run's a self test. try koeo and see if electric motor functions when you step on the brake. if not then look into that system. it could be a bad motor or the switch still could be defective. it just may be unplugged. i'm not 100% sure on this, but i think i read that the trailer brakes may be tied into the alarm system if it came factory installed. you're 100% correct when you state that there is two issues here. the abs is completely isolated from the low pressure system warning. tina's probably correct about the toner ring. could be just mudded up or are corroded because they're white metal, someone thought white metal was better than steel because of the rust. they must never have been in the north. is there a brake function in global? i'm not sure because we have a tech 2.

[protraxrptr17]

Yes the flow switch is the switch you speak of (which is new). The electric pump works just as it's supposed to. I assume the flow switch works because if you hit the brakes when the engine is off, the pump turns on. I tried jumping the brake fluid level switch and it didn't help either. I want my truck fixed, but my main concern is getting my scan tool to work with these trucks.

[steven kiser]

hate to make false promises but i have to call my g.m. truck supplier today. if i can get him to talk to a tech i will. i'm as busy as a one legged man in an a** kicking contest and i may drop this but will remember soon enough. ya, i know i'm not making sense.

[protraxrptr17]

Thank you. Maybe he can telll us a vehicle that has the same brake system and we can enter the VIN as that vehicle and get in.