I am writing about my 2004 A6 avant, which has 78,000 miles. At a recent oil service at an independent garage, it was suggested that there was a problem with the catalytic converters. Exhaust was leaking from both sides, I was told. I took the car to my Audi dealer, where they checked the exhaust system. The mechanic who examined the car concurred that the catalytic converters needed to be replaced. Under a federally mandated warranty, the catalytic converters are covered for eight years or 80,000 miles. Yet the dealer has declined to cover replacement because the "check engine" light was not on. I was given a repair estimate of $2,400.

- Millburn, NJ, USA