Problem Description and Possible Solution
Vacuum leaks, oxygen sensor failure, and catalytic converter efficiency faults can cause the Check Engine Light to illuminate.
Average mileage: 101,960 (55,333–210,000)
Exhaust & Emissions affected: 1.8L 4 Cylinder Turbo
27 people reported this problem
Appears to be the caused by the failure of the air pump and air valve. Apparently a common problem as I have a friend with a simliar age TT that has the same issue. The pump keeps the fuel tank pressurized so if it fails the diagnostic system thinks there is a vacuum leak.The car will fail an emisions test, but the car is still usable until you can get it fixed. Cost is around $800.
I have had my car in the shop several times due to Vacuum leaks, oxygen sensor failure, and catalytic converter efficiency faults that cause the Check Engine Light to illuminate, to the tune of approximately $1500 over the past year. Both repairs were made between 90-95K miles(currently has 96K miles). Now I'm looking at possible modulator failure. Doors won't lock, inside lights don't work, convertible top doesn't work, and car doesn't recognize key remote! Air bag light is on also???
Replaced rear O2 sensor didnt solve problem,tested old one it was still good. Put a heat gun at front of catalytic converters and back of them wide difference in temperature range from front to rear of cats. That tells me cats are pluged,so bought 2 new ones waiting to get installed,that should remedy problem,Ill update after installation.