This is getting stale (earlier post on 6/27/14). Replaced the CTS around August in my wife's 05 B6 3.0 because after sitting out in rain, the CEL would randomly come on (along with a few misfire or fuel related codes and a brake vacuum boost code). Audi had the car in mid December and replaced the Brake Boost Vacuum pump, a relay, and a leaky vacuum hose. Last night, CEL pops on again with the following codes (I've seen this set of three before but always the P0118 sets the CEL):
17537 - Fuel Trim; Bank 2 (Mult)
P1129 - 002 - System too Rich - Intermittent
16559 - Fuel Trim; Bank 2
P0175 - 002 - System Too Rich - Intermittent
16502 - Engine Coolant Temp. Sensor (G62)
P0118 - 002 - Signal too High - MIL ON
Readiness: 0000 0100

I did notice this time that one of the cooling fans starts spinning fast as soon as the ignition is turned on - very reminiscent of a fan control module issue I had on my kids MkIV Jetta (actually the culprit was the High Pressure AC sensor). Assuming the CTS is good (Audi part and only a couple of months old but maybe a bad assumption), what else could cause the CTS to set a CEL and is there a relationship between the other two codes (it's always Bank 2 by the way)? No coolant loss and dash temp gauge is right were it should be. 99700 miles on the car. T-belt, thermostat, and water pump done at 67K.
TIA,
AJG