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I recently blew a rear brake line do to a corroded rear passenger hardline. I repaired the line and bled the brakes and was still left with code c1247 brake pressure differential switch activated. I tried to reset the code but I couldn’t erase it. I lost the use of the traction control button and active handling.
After some research I found that the switch was located on the brake combination valve under the master cylinder.
The fix is to take off the windshield wiper fluid reservoir and unplug and remove the switch from the brake combination valve (17mm open end wrench.) Once removed you will need to side the bolt forward or backwards to align the sight hole with the valley of the bolt. Then the plunger on the switch will be fully extended and there will be no more c1247.
If there is still a code reset it through the DIC and it will be erased. No more code and active handling now will work.
This is not the gm valve I just used a stock photo to explain what is happening inside the unit.
C1247 Reset
