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Discussion Starter #1
I'd greatly appreciate some help troubleshooting a P0420 code on my '07 OB. I've reviewed many posts on this, including the P0420 Diagnosis post on the Problems and Maintenance forum, but I'm not understanding some of the basics. Many of the posts refer to checking for exhaust leaks. How do I conclusively figure out if exhaust leaks are the issue for P0420? Today I put the car up on ramps and got under while it was running. I did not hear any air hissing or feel any major puffs at the joint between the exhaust manifold and the front catalytic converter. I also had two people hold rags against the two tail pipes while the car was running. Again, I did not hear any air hissing while under the car. When the rags were against the tailpipes, the idle didn't noticeably drop. Is that normal? What's the right way to diagnose exhaust leaks for P0420?

Below is a timeline of what's happened so far. Can anyone recommend next steps?

Aug. 2019 - CEL went on; odometer was around 110,000 miles; shop reported P0420 code and advised catalytic converters likely need replacement; shop cleared CEL; around two weeks later, CEL went back on.

Sept. 2019 - CEL still on; I replaced the air filter and spark plugs and added one can of BB 44K fuel treatment to the tank, then drove the car on the highway for 45 minutes; CEL remained on.

Feb. 2020 - CEL still on; I took the car in for an oil change; shop reported the P0420 code and again advised catalytic converters likely need replacement; shop cleared CEL; shop suggested trying another can of BB 44K fuel treatment, but this time with high octane gas in addition to 45 minutes of highway driving, which I did.

May 2020 - CEL stayed off until May, but then went back on; few miles were driven since March due to pandemic; I don't have a code scanner, but I assume it's P0420 again; I checked for exhaust leaks as described above.

I plan to buy a Veepeak OBDCheck BLE OBD2 plug-in and download the OBD Fusion app so I can get the codes and ECU info, but if another tact would be better for getting diagnostic info for this, I'm interested in hearing about it. All my phone and laptop devices are Apple OS.

Thank you very much!
 

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Discussion Starter #3
Yep, I saw that--pretty cool. There's actually similar feature for the audio system where it will give a diagnostic read-out on the screen if you punch in a specific sequence on the knobs. Thanks for the link. If any thoughts come to you later about next steps for me, I'd appreciate your sharing.
 

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Discussion Starter #4
I should mention, using the on-board reader suggested by plain OM, I confirmed the CEL code is P0420.
 
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