Car Doctor Q & A: An Insider Tip to Finding an Exhaust Leak

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AAA Car Doctor John Paul provides some advice on figuring out where an exhaust system might be leaking.

Q. I have a problem with my car that generated a PO420 code. The code is as I understand could indicate a problem with the catalytic convertor. I’m trying to do the work myself. Based on a recommendation I replaced the oxygen sensor and that didn’t work. The latest suggestion is that there is an exhaust leak but I can’t find anything. Do you have any ideas?


A.The PO420 code can be caused by a variety of items including a faulty catalytic convertor, leaking fuel injectors, EGR valve issues and a leaking exhaust system. Here is a trick to test for a leaking exhaust system. When the engine is cold use a shop vacuum or leak blower and attach it to the tailpipe. With the shop vacuum or leaf blower turned on you should easily be able to find an exhaust leak. This is a great trick to find a cracked manifold that seals up once the engine is running and warms up.

John Paul

John Paul

1 comment

  1. I’ve also heard that a PO420 code signals and exhaust leak in my car. Like your reader, I also couldn’t find anything wrong with my exhaust pipe, so I’m looking for answers concerning why my car has a PO420 code right now. I didn’t realize that there are many causes for it. It seems like I should check on for a faulty catalytic converter or a leaking fuel injector, since those two are the most likely possibilities in this list for why my car has a PO420 code. Thanks for posting!

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