I have a 2001 Passat 2.8L V6 with 92,000 mile
Recently the Check Engine light went on with "Emissions Workshop" message. The dealer replaced the "Coolant Temp Sensor" for $200 and I got the diagnostic paper:
16502 P0118 035 Engine Coolant Temperature Circuit High
17831 P1423 035 Bank1, secondary air system air flow too low
17819 P1411 035 Bank2, secondary air system air flow too low
After a day, the Check Engine light was on again. Now the diagnostic says:
16815 P0431 035 Warm Up Catalyst, Bank2 Efficiency Below Threshold
16805 P0421 035 Warm Up Catalyst, Bank1 Efficiency Below Threshold
The dealer offered to change both converters (cat) for $3000.
This in insane, because the car is running perfectly, so it must be only a sensor problem or something other minor stuff (O2? thermostat?).