2002 Audi A4 help

You aren't going to enjoy the noise on long trips, and you sure won't win the appreciation of your neighbors, but as long as you keep the catalytic converters and all of the oxygen sensors, there shouldn't be a problem with the Engine Computer. The rear oxygen sensors monitor the efficiency of the catalytic converters. Based on what they report, disabling anything related to them will set diagnostic fault codes and turn on the Check Engine light.

There's two problems with driving with the Check Engine light on. First, if another problem develops that would also turn the light on, you'll never know since the light is already on. That can turn a minor problem into a very expensive one if it is unwittingly ignored. Second, the Engine Computer compares a number of sensor readings and operating conditions to each other to, in part, determine when there's a problem. If there's already a diagnostic fault code set for something that's used for comparison, other tests that use that information may be suspended. The cause of a running problem could go undetected, and without the fault code that would have been set, there's almost no way to know where to start looking.