Hey guys,

Today I am driving on the freeway, semitraffic my engine light comes on and I check the code and it pulls a 0421 which is Warm Up Catalyst Efficiency Below Threshold (Bank 1). The car drove fine till I got off the freeway. I cleared the code and drove on normally. I have a intercooled turbo lancer pushing 7 psi. Does anybody know what this code means and what might have caused it? Thanks for the help.

 

Sounds like because of the turbo and the exhaust gases having to pass through the cold manifold and turbo before getting to the cat, the cat isnt warming up in sufficient time, so it is telling the ECU that something is wrong. DO you let your car warm up, or do you stomp on it and go? Usually, it is no cause for concern as it does not affect driveability (do any CELs do? Not in my eyes ) ...... It is more of an emissions thing.

It could be something more serious too, but from the sounds of it, I wouldnt be too worried.

EDIT: I see you live in Cali, aka the land of the emissions test, so you might need to square that away.

 

Since I got the turbo, I really dont let it warm up. Bad idea? So its an emissions thing?

 

YOu could let it warm up as it is a code for cold starts. But if you dont, I wouldnt worry too much about it.

It could also mean that your O2 sensor has gone bad or that your cat. is bat, but I doubt it. Since you are turbo, it probably just means that the cat isnt warming up in enough time, and if you say there are no negative side effects, i wouldnt worry too much.

 

i don't have a turbo and i just threw the same code tonight on the highway. i'm at 67,000 miles. I have been running 93 octane only because I was anticipating getting my new rrm piggyback and looking to install as soon as it arrives. it took 4 weeks to arrive so i've been driving on 93 for 4 weeks. i think that might have caused my first o2 sensor to go bad. any thoughts?

 

93 octane wont cause your car's O2 sensor to go bad.... only if you run some high octane leaded fuel, that would cause it. Your O2 probably went with age. Mine took a dump on me, maybe about 80K miles. Probably a bad O2 sensor is my diagnosis. Change yours and see if it remains.

 

If I'm not mistaken, 0421 is what I've been getting since I got header, so I wouldn't worry about it either.

 

Since you dropped a few thousand on a turbo that is easy to destroy, YES, it would be wise to let the car warm up for a couple minutes before driving.

Heck, just the investment in a car would necessitate letting it warm up in my eyes. I paid $14000 for my car (more after interest), and I'm not going to harm it because I'm impatient.

 

my car just threw the same code at me yesterday, so i came to search the forum for answers. I have a 2003 OZ w/ RMR SRI and custom catback as far as mods go. Any ideas why this came up. I to do not let my car warm up i crank it up put in gear and go with it. My mileage is 25k total and ~9000 w/catback and SRI installed. It is too new for the O2 sensor to have gone and the muffler shop did not touch my cat, besides i still get the same MPG 23-27 as before. I just want someone to assure me that my car is fine. I do not want to have to go to the dealer w/ mods and they BS me about warranty voided.

 

I have the same code. I think the cause is the heater part of the 02 sensor has gone bad. I plan on changing my front 02 sensor before winter. I'll tell you what happens but if someone does it before me, please respond on the out come.

 

i currently have the same code. my car threw it once i put on my headers, it is because the headers removed the first cat from the stock manifold, it has no relevance with letting your car warm up (i always allow mine to warm up for about 5-10 min before driving). since you dont have headers, it is either an o2 sensor that is out or i have even heard of an intake throwing the same code-or maybe its 0420, but im pretty sure it is 0421. my best suggestion is having a shop or dealership further diagnos the problem. good luck.

 

Well i can certainly comment on O2 sensor replacement, since i did that today. I got the sensor from Oxygensensors.com was like 51.xx You just clip your harness off and crimp/solder it onto your new sensor. I crimped mine and its been running fine, except a ac problem (but that has to do with my turbo) plus my cel light went off after i replaced it and hasnt come back on yet

But also, mine threw a P0135 code which is bad sensor....

 

If you have a header you usually get the code for the first cat not heating up fast enough... especially if your turbo and have the header.

If it isn't flashing a bad sensor code your fine... what you can do to keep it from coming back is put another bung on the 2nd O2 sensor or an anti-plug fouler. This will make the 2nd sensor sit away from the heat more. Thus the temp difference between #1 and #2 will be increased and this is what the ecu is measuring. If they are to close to the same... which is the case when you add a header/turbo... then the code will flash. It won't affect driving but it can be annoying.

Easy fix though... for more info on it check out the evo forums as they do it all the time to get around that code.

 

What about flipping the cat? Or is that a solution to a different O2 sensor problem? Hard for me to say with any certainty since I don't get CELs anymore.

 

so basically the car will be fine i just will have to deal with the annoying CEL and resetting my ECU. No big deal i am just glad my engine is okay.