Service Brake System Message...

Mark Francois · July 20, 2020

I've been getting an intermittent Service Brake System Message along with the ABS light and Parking Brake warning light on my 2003 GMC Yukon 2wd with the 4.8l motor. Sometimes it will be days or a week or two between getting the message or maybe one day to the next but they always clear up after I drive a little, stop and restart the truck,. Sometimes it is as quick as just driving just a couple hundred feet and restarting the truck or it may be when I reach my destination. I'm hoping that it is just an intermittent failure from one of the front ABS sensor but is there a way to check the sensors out with a multimeter to make certain that it is them or just a way to trouble shoot the system in general. It is kind of a tough one since it is an intermittent issue. Thanks in advance!

makingterrificdecisions · July 25, 2020

I've got simlilar message. Service brake booster. Read up on it and it could be many things including:

- replace brake booster or vacuum pump (wasn't for a silverado though)

- poor contact of the sensor due to rust/corrosion

I can't remember the last one, but best to take it to a mechanic because it seems pretty random

davester · July 25, 2020

It's also common for the ground connection to be a problem for the abs computer. It's located on the wing, just off the frame under the driver's seat. Unbolt the wires from the wing, clean the connectors and the wing, bolt them back down and smear some dielectric grease over them.

Mark Francois · July 28, 2020

Thanks guys, I'm guessing that you mean these two grounds attached to the body mount perch under the drivers footwell just behind the front wheelwell? If so, I'll clean them up and put some DI grease on them this weekend.

Edited July 28, 2020 by Mark Francois
added picture

davester · July 29, 2020

Yup, those are the ones.

Mark Francois · July 29, 2020

18 hours ago, davester said:

Yup, those are the ones.

Cool deal! I’ll try what you suggested this weekend. Thanks.

Mark Francois · July 30, 2020

Well, the grounds were not the issue so I got off my lazy butt and tested the sensors themselves. What I found was that the passenger side sensor output was half the voltage (AC) of the drivers side. I belive that testing the sensor with a multimeter on AC while spining the tire is the proper way to check function. I know that the rate in which I spun each wheel was not exact betwen the two but it wasnt so much of a difference that the voltage should differ by half. What do you guys think? Something else I noticed while troubleshooting this issue is that when not in alarm, unplugging the drivers side sensor only illuminated the abs light but when unplugging the passenger side sensor tripped the abs and brake icons in the dash. Is this the intent to help mechanics differentiate between faulty sides or am I seeing something else and don’t realize it?

Edited August 3, 2020 by Mark Francois

Mark Francois · August 8, 2020

Well, changing out the front two abs wheel sensors didn't fix the issue. At first it seemed right but then it lot up again then it was off and then it was on again lol I didnt mind the work it took to swap those out but dang I’m tired of this intermittent problem garbage!