Since I picked up my vehicle at auction it has had the P0420 code for efficiency bank 1. I have noticed no issues in performance and gas mileage is normal. I am having issues with Techstream and getting live data to help diagnose the issue. I understand this could be a bad cat, O2 sensor or possible leak in the exhaust system. I do know that I have a bad flange on the passenger side right after the primary cat, which was repaired with exhaust putty but it is leaking again. Surprisingly that side is not throwing any codes.

I had a mechanic say that 99.9% of the time that code indicates a failed cat and on the LS600 he said it looks like the engine has to be pulled to give access to the exhaust manifold. I understand things are tight but find this hard to believe but haven't looked into it in great detail. How hard of a job is it to replace the driver's side cat on a 2008 LS600H?

Here in PA we have to get yearly inspection/emissions testing and I'm coming due. Looking for suggestions on best way to diagnose. I have read about possibly getting a custom tune. Any info on that route? Thank you.

 

It runs in my mind that there was a thread (or at least a post) about this exact issue in the last few years. In that case, if memory serves, the repair was completed without pulling the motor. Suggest you spend some time doing a search. Good luck!

 

Hi Mattyman. I believe the history on that car showed the entire exhaust being replaced twice. In any case it might help to look up the history again to see if one or both of the cats were also replaced. Can you clear the codes to pass inspection?



This is the thread with the talk of removing the codes from the firmware so they don't fault, pretty nifty. You'll probably have to message one of the members to get the contact info of the guy that can flash the ecu. I'm not recommending you do that, just giving you options. I'd be concerned the car would still fail your inspection.
https://www.clublexus.com/forums/ls-...nverter-2.html

This thread has some tips on diagnosing what the cause is.
https://www.clublexus.com/forums/ls-...st-system.html

 

miket000, thank you for the info. I checked the service history on the car and it looks like only the mufflers were replaced. This one recently had the brake actuator and control arms replaced, which is a benefit. Car has been running great even with the code. I might try running a bottle of cataclean through it to see if I can clear the code enough for emissions or maybe the non fouler trick. When I get some time, I'll spend some more time under looking for leaks, etc.

 

If this is just for inspection, you can clear code and monitor all systems are ready with OBD2 and Torque app and take it to the inspector.
the p0420 requires certain drive cycles to complete diagnostics and turn back CEL.

 

I had the same code on my 430. It was a bad gasket on out put of cat. Always got the wrong one from advance auto. Burnt out every year. Researched and found correct part number from south Atlanta and ordered them from Amazon cheaper and in stock. Stayed fixed from then on.

 

Had the same code on my 600. Turned out to be a bad o2 sensor . The dealership and an Indy said the engine and transmission has to come out. Took it to my guy who fixed it in 3 hours in clouding cool down. I would try that before replacing the convertors.