This code has shown up after replacing the coolant sensor and establishing readiness. Any ideas how to fix this. Bentley suggests checking the harness and if that doesn't work out, replace the ecu. That seems pretty drastic for a coolant sensor.
The car car has 44000 miles and GIAC X+ otherwise stock.
VAG-COM Version: Release 607.2-UD
Control Module Part Number: 06A 906 032 PL
Component and/or Version: 1.8L R4/5VT G 0003
Software Coding: 07510
Work Shop Code: WSC 65728
Additional Info: 9BWDE61J824058923 VWZ7Z0A4434738
1 Fault Found:
18613 - Performance Malfunction in Cooling System
P2181 - 35-00 - -
Readiness: 0000 0000