96 SLS problems...

My neighbor has a 96 Seville SLS with the Northstar engine. He came home this weekend and the trans would only go forward in second gear. Reverse, neutral, and park all work great. The trans does not slip and the fluid looks good. He pulled two codes - p1602 and p1571. It looks like they both have something to do with the EBTCM - electronic brake and traction control module. Could this part have failed, causing the transmission to stay in second while in forward gears?? He would like some input before dropping $800.00 in parts on this car. Thanks in advance!! Sincerely, Dave.