Originally Posted by Tightwad
"IF" the correct converter was installed and O2 sensor is ok sounds like whoever installed the converter messed up somehow.
To the OP, you'll be fine with an aftermarket converter as long as you stick with a brand name part. Magnaflow is a good product. Saving $800 is another good reason to go aftermarket. You should have your local mechanic confirm the dealer's diagnosis before replacing any parts.
If the dealer's diagnosis was a bad converter, will they still apply the $100 toward a different part (oxygen sensor)?