For $29/mo, we provide access to advanced level technicians who will answer your questions on any Macbook board related matter to the best of their knowledge promptly & walk you through how to solve your problem so you can deliver a working board to your customer.
Check for crap around U4820/30. These chips loop back to the trackpad via i2C bus, so it could also be a bad trackpad or flat cable. My bet is TP or cable.
I do not have the BV for this one, not needed for a simple repair like this.