Smog issue... - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

madpeanut · 05-29-2025, 09:13 PM

I'm getting a P0420 error code, catalyst system efficiency below threshold bank 1.

I have replaced the up and down stream cats, my understanding is bank1 is driver side:
https://www.oreillyauto.com/detail/c/california/magnaflow-california-catalytic-converter/mgfc/557406/v/a/30402/automotive-car-2010-chevrolet-camaro

https://www.oreillyauto.com/detail/c/california/magnaflow-california-catalytic-converter/mgfc/551006/v/a/30402/automotive-car-2010-chevrolet-camaro

I have replaced the up and down stream O2 sensors on both sides too.

I've cleared the code and literally a day later the check engine light comes back on. I've also swapped the cats twice just in case.

Yes I got these from oriely but they are magnaflows and I bought these a few years ago and had no issue. Some people hate orielys, some hate autozone but they wouldn't be selling these if they didn't work. I know CA has extra rules but both of these are approved for use on this make/model.

Any ideas? How can I find a place that can help me work on this in the Los Angeles area, sounds like I need a smog repair vs regular mechanic?

P.S. - I dont think this is it but I remember the last time I had to do this it took some time for it to re-register the emissions before I could go get it smogged but I dont recall the light coming back on until its registered but maybe...? (I'm seriously grasping at anything at this point)

PPS - Performance gets reduced when the engine light comes on. If I clear it, performance returns, so I'm thinking it's in some limp home mode.

KillboyPowerhead · 05-30-2025, 05:51 AM

Bank 1 is the passenger side.

Not sure how emissions testing works but I believe if you clear any codes the testing equipment knows and will see that certain tests or modules aren't "ready", and so you'll need to drive around a bit until all tests have been completed again.

Shouldn't get any reduced performance when the 0420 condition exists. When I installed Mace cams I got the P0420 code a few weeks later (already had high-flow cats on for a few years with no issues), but no change in performance.

gtstorey · 05-30-2025, 09:05 AM

Quote:

Originally Posted by madpeanut

but they wouldn't be selling these if they didn't work.

Not really true. Both sell a lot of parts that don't work or fail in a very soon.

TheBrightSide · 10-06-2025, 01:24 AM

Any updates on this? Did you try checking out all 4 of the oxygen sensors?

05-29-2025, 09:13 PM	#1
madpeanut Drives: 2010 Camaro v6 RS Join Date: Aug 2016 Location: Los Angeles Posts: 1	Smog issue... I'm getting a P0420 error code, catalyst system efficiency below threshold bank 1. I have replaced the up and down stream cats, my understanding is bank1 is driver side: https://www.oreillyauto.com/detail/c/california/magnaflow-california-catalytic-converter/mgfc/557406/v/a/30402/automotive-car-2010-chevrolet-camaro https://www.oreillyauto.com/detail/c/california/magnaflow-california-catalytic-converter/mgfc/551006/v/a/30402/automotive-car-2010-chevrolet-camaro I have replaced the up and down stream O2 sensors on both sides too. I've cleared the code and literally a day later the check engine light comes back on. I've also swapped the cats twice just in case. Yes I got these from oriely but they are magnaflows and I bought these a few years ago and had no issue. Some people hate orielys, some hate autozone but they wouldn't be selling these if they didn't work. I know CA has extra rules but both of these are approved for use on this make/model. Any ideas? How can I find a place that can help me work on this in the Los Angeles area, sounds like I need a smog repair vs regular mechanic? P.S. - I dont think this is it but I remember the last time I had to do this it took some time for it to re-register the emissions before I could go get it smogged but I dont recall the light coming back on until its registered but maybe...? (I'm seriously grasping at anything at this point) PPS - Performance gets reduced when the engine light comes on. If I clear it, performance returns, so I'm thinking it's in some limp home mode.

05-30-2025, 05:51 AM	#2
KillboyPowerhead Drives: 2015 Z/22 Join Date: Aug 2015 Location: Ontario, Canada Posts: 983	Bank 1 is the passenger side. Not sure how emissions testing works but I believe if you clear any codes the testing equipment knows and will see that certain tests or modules aren't "ready", and so you'll need to drive around a bit until all tests have been completed again. Shouldn't get any reduced performance when the 0420 condition exists. When I installed Mace cams I got the P0420 code a few weeks later (already had high-flow cats on for a few years with no issues), but no change in performance. __________________ Overkill/Self Tuned; Mace Camshafts; K&N Typhoon Cold Air Intake; Ported 80mm Throttle Body/Intake Manifolds/Manifold Spacer; Solo Performance High-Flow Cats, Cat-back Exhaust; Vitesse Motorsports Throttle Controller; Elite Engineering E2 Catch Can; BC Racing BR Coilovers; JPSS Delrin Radius Rod Bushing Inserts, Sway Bars; Pegasus Aluminum Rear Cradle Bushings, Camber/Caster Plates; Z/28 Toe Links, Trailing Arms, Upper Control Arm Bushings, Rear Shock Mounts

10-06-2025, 01:24 AM	#4
TheBrightSide Drives: 2010 Chevy Camaro 2SS coupe (MT) Join Date: Jan 2024 Location: Sacramento, CA - USA Posts: 367	Any updates on this? Did you try checking out all 4 of the oxygen sensors?