Q: Bypassing catalytic converter with a test pipe

This is against the law. You are not supposed to give it in catalytic converters. That’s why it’s called a test pipe. People put them on as a test and then if the car runs better, they know that the cap’s gone and then they replace it. Of course, there are a lot of places, like Montana, where no one ever checks it. The people there tell me they take them off and they drive them and the vehicles run fine. The Check Engine Light might come on but you are breaking the law, so you are not supposed to do that. If you want to have the Check Engine Light inspected and properly resolved, a technician from YourMechanic can come to your home or office to perform these services.