Replaced my TT 225 roadster for a 05 S4 cabriolet. She threw a code, Advance Auto pulled my codes and showed both cats were bad. Two weeks went by beforeI could schedule a visitto the dealership to get cats replaced under warrenty (federal), they recommendedthat the plugs and coil packs (old part number) were changed, wanted $800, told them I would do it myself. Also said temp sensor was bad, gauge work fine, wanted $300 to replace. Wanted $184 for a part that cost me $21 (green sensor), looked all over the net and haven't found the location of the coolent sensor on a 4.2 liter, can anyone help me? Pictures would be useful. Oh, car is no longer under warrenty so that is why I would rather perform these simple repairs.

 

If memory serves me correct the sensor is in the coolant pipe at the rear of the engine that connects the two heads. I dont remember which side but its probably closer to the passenger side head.