Replace computer or additional diagnosis? Computer program requires dealer only? on 2002 Nissan Xterra

Problem-rough idle, stalling, rough running .
Repair#1-accessory belts, shocks replaced; knock sensor replaced. After repairs service engine soon light illuminated. Told wires shorted- need a computer
Repair#2- has a code for idle air control-valve will not operate; wires damaged at the connector, shorted. Repair wire harness and installed new idle control unit. System not working properly-computer will not operate valve on demand. Referred to Nissan for computer reprogram or replace.
Service #3-Nissan suggested extensive diagnosis (follow the wires) to determine problem. Est 4 hours to diagnose
Is it true that only Nissan dealer can program computer?

Get Your Car Fixed at a RepairPal Certified Shop.
We certify shops based on expertise, quality work, and verified customer reviews
1 answer
yep only dealers can flash ecm