Quote:
Originally Posted by tpr60
I've had a couple GM trucks that set abs codes because of hub/bearing assy. being worn/loose. Since c4 has a problem with hubs after hard use, I'd be checking them next.
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This looks to be a great place to start, hubs and slop and/or cleaning around the sensors looking for ferrous material near the sensors.
By the OP description this is going to be an intermittent issue. Always fun. I'd stay focused on the first error that comes up, 21.
Good luck.
You have an opportunity to add to the collective knowledge here when you find the cause. Take pictures
