Service Brake Light on After doing rear brakes.

[Saucy_Walnuts]

On my 2003 GMC Yukon, I replaced the rear parking brake shoes and pads. I had to compress the caliper pistons to get them on with the new pads. Now I have a Service Brake System light on and not sure why. No ABS on or anything. My scan tool can't read the code that may be present. Any help would be appreciated. I did do some research and it may be a proportioning valve stuck or a EBCM problem? How difficult would it be to fix the possible sensor under the brake master.

 

[03yukXL]

I had the same thing happen. Somebody on this forum offered the advice: make sure the master is full on fluid and mash the brakes aggressively to the floor. To my surprise it worked perfectly, light went off. I was driving on a private road about 25 mph when I did it, but in retrospect I’m not sure if I needed to be moving at all. Hope that helps!

 

[SpareParts]

You need to be moving fast enough on a dirt road so that when you mash the brakes it cycles the ABS system. Sitting still the ABS will never activate.
If you don't have a scanner that can activate the ABS, mashing the brakes on a dirt road essentially does the same thing a scanner will do.
Under 5 mph, the ABS will not activate.

 

[Saucy_Walnuts]

You need to be moving fast enough on a dirt road so that when you mash the brakes it cycles the ABS system. Sitting still the ABS will never activate.
If you don't have a scanner that can activate the ABS, mashing the brakes on a dirt road essentially does the same thing a scanner will do.
Under 5 mph, the ABS will not activate.

Did that about 5 times. No difference, but I did find out when I unplug this sensor for the proportioning valve it goes away. I do have a parts truck i could get it off of. Would i be able to "reset" or clean said valve and sensor? I think there is a piston of sorts in there from what research I did last night.

 

[Fless]

Find a scanner that will read the code.

 

[Saucy_Walnuts]

Update: after doing some talking and digging it turns out the proportioning valve piston was too far forward causing the sensor to read wrong. After bleeding the front brakes it brought the piston back to center and light went away. Turns out this can happen when compressing caliper pistons on these trucks.