ddtham

Hi guys,


I just recently bought a 97' C280 with 120k miles on it. After driving the car for a week, the check engine light went on. So, I brought the car to Autozone for an OBDII scan. The OBDII says P0422, main catalyst efficiency for bank 1 is below threshold. Can you guys tell me whats P0422 code is?

I just want to know whats wrong with the car before I bring it back to the dealership to get it fixed under warranty. Thank you so much.


DDTham

krusty

It's a code set by your system by the rear (post cat) O2 sensor. It means that this sensor's output is being seen to be following the front sensor output. It shouldn't. Your cat is apparently not functioning as it should, and probably requires replacement.

A word about aftermarket vs. OEM cats;
I just replaced the cats on my C36 with high-flow aftermarket ones. I promptly started getting that code showing up every drive cycle. The HP cats were useless on that car, so I replaced the dual setup with a single Magnaflow unit with appropriate inlet and outlet pipe size and the correct capacity. It has been fine. No codes, and was a whole lot cheaper than OEM. I also lost a tremendous amount of power with the high flow cats on the C36 as well as having my fuel mileage improve. This is because with the aggressive cam overlap, I was losing a lot of intake charge out the exhaust as there was no back pressure to prevent it from leaving while the exhaust valve was still open. The O2 sensor saw that, and leaned the mixture out accordingly, hence my mileage improvement. I also trashed the cats very quickly due to the unburned fuel in the exhaust until the computer adapted, so the P0422 code was set repeatedly as quickly as I could erase it. The OEM cats are the correct ones, but careful selection will allow the use of aftermarket ones. Resist the urge to "improve".

ddtham

Thank you so much for your reply, it really helps me learn stuffs. Actually my car is experiencing bad acceleration and bad gas mileage as well. Do you think it needs new O2 sensor as well as new cat back?. Thank you again.



DDTham

krusty

First things first. Get the converter replaced. If it is damaged internally, it can cause the P0422 code as well as your poor power and fuel mileage due to restricted exhaust flow. Have them set the car up on their diagnosis equipment and tell them to specifically look at the front O2 sensor. There has to be a reason that the cat failed, and a bad sensor can do it, however it usually sets a code of its own.

ddtham

I went to Meineke yesterday. They said that the converter on the left is broken, thats why there is like a rattling sound everytime I start the engine, and coming to a stop. They quoted me $175 for a universal replacement on the broken converter. I'm just wondering if universal replacement would work with our cars or not? Thank you so much again.


DDTham

krusty

Yes, some universals will work, but modifications will be necessary. You won't be able to fit most replacement cats into the side by side original space, and ones that will fit will be high flow types for much smaller engines. Don't run with mismatched cats, and the other one is probably not far behind the first one for failure. Magnaflow makes several good stainless steel universal cats that will have more than enough capacity for your engine and are not expensive ($60US or so from Summit Racing last I checked). Have both cats replaced with a single oval cross section cat. It will flow far more than enough, so don't worry about back pressure being elevated. They will have to fabricate the front transition piece from the down pipes to a single converter, but that is easy for an experienced shop. A lot of cheap aftermarket or high flow cats will bring the same code in on you in short order, but the Magnaflow ones won't. There are probably a couple others that are good too but I have personally tried Magnaflow with success after failure with another brand of dual cats.