Hey Everyone, I have a 2003 Lexus IS300 with Intake, Headers, Downpipe, and Cat Back Exhaust. After i had put all of this in my check engine light turned on so i scanned it with the diagnostic scanner. It came up with error code P0420 which is Cat Efficiency Below Threshold, Bank 1 and P0430 Cat Efficiency Below Threshold, Bank 2. Does anyone know what could be causing this problem? Will I be able to fix it?

 

Oh yeah I got My AFC NEO in along with my Computer Controller

 

I think that without the precats (replaced by headers) that the stock cat is not up to snuff. I have no precats on my RX but I do have a high flow cat from Magnaflow (a 3 way that does the job of the original cat and the precats) and no such errors, though my uncle and I have worked on a few vehicles with the P0420 code and it ended up being a dead cat.

 

Bad cats are kind of rare, but not completely abnormal at my shop. See if the local Lexus dealer will replace it free of charge, since it's directly related to the Emissions Warranty (8 years/80,000 miles in most states). As long as you didn't tamper with them, they should cover parts and labor.

It never hurts to have them check them, but understand while the repair doesn't take long, the cool-down time for handling the old cats on your car can take an hour or so.

 

The reason its throwing those codes is because o2 sensor bank 1 monitors exhaust gases from cylinders 1-3 shares one cat and o2 sensor bank 2 monitors exhaust gases coming from cylinders 4-6. By removing the 2 cats it throws bank 1 reading off because there is no cat to reduce emissions therefore bank 1 sensor 1 and bank 1 sensor 2's readings are the same and it would be same for bank 2 sensor 1 and 2. If the sensors readings for each bank are mirroring each others voltages then it will throw a cat efficency code, because the PCM does not think the cat is doing its job.

caRLin

 

okay thanks for your knowledge guys. sorry it took me so long to reply i havent checked the forums in a while. My question now is will my car pass smog w/o the pre cats? and is there a way for me to keep my headers and exauhst and get rid of these error codes?