What is p0421 - Cars & Trucks

Yes it is and it would mean that the problem that caused the P0421 has either been corrected or is intermittent and is no longer in the state causing the failure. P0421 is a code for Warmup Catalyst Efficiency so there. Like be an intermittent problem with an O2 sensor or the catalytic converter may be starting to clog.

C1201 error code means that you have some problem in engine control system.

Possible causes for P0421 error

• Warm Up Three Way Catalytic converter deterioration or malfunction
• Exhaust system leaks
• Loose front or rear HO2Ss
• Faulty front heater O2 sensor
• O2 sensors harness is open or shorted
• O2 sensors poor electrical connection

The P0421 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem.

P0421 code is that the cat. converter is below efficiency. 99 per cent o the time the cat. needs to be changed. but if you have a scan tool watch both bank 1 O2 sensor 1 and bank 1 sensor 2.
cold they should be almost the smae but when its at operating temp, and running down the road at crusie speed the frt o2 should switch rapidly between .150 mv. and .850 mv. and the rear o2 should read about .600 mv. if they read the same the cat is ng and will have to be replaced.

my 2001 mazda 626 V-6 have a error code p0421 & P0421 so how do i fix it. tell me the causes and the solution

PO421:Warm Up Catalyst-below threshold (bank #1) CEL

taken from: http://forums.evolutionm.net/lancer-troubleshooting/349095-code-p0421-call-mitsu-before-you-do-anything.html

Code P0421- Call Mitsu before you do anything! Icalled my nearest dealership today and for those who dont know, if yourcheck engine light is on and its showing fault code P0421 this may befrom a factory recall on the warm-up converter and a PCM reflash.MILEAGE OF THE CAR DOES NOT EFFECT THIS RECALL. Anyone whos had problemwith a dealership not doing the repairs because of mileage needs tocontact another dealer or the owner of the dealership. This is what theservice manager told me today so though I'd share. Getting mine fixedtomorrow at 10am, I cant wait.

For more information about this code Google "Fault Code P0421" You'll get tons of information Last edited by Swankzer; Jun 2, 2008 at 12:31 PM.

taken from: http://forums.evolutionm.net/lancer-troubleshooting/349095-code-p0421-call-mitsu-before-you-do-anything.html

Code P0421- Call Mitsu before you do anything! I called my nearest dealership today and for those who dont know, if your check engine light is on and its showing fault code P0421 this may be from a factory recall on the warm-up converter and a PCM reflash. MILEAGE OF THE CAR DOES NOT EFFECT THIS RECALL. Anyone whos had problem with a dealership not doing the repairs because of mileage needs to contact another dealer or the owner of the dealership. This is what the service manager told me today so though I'd share. Getting mine fixed tomorrow at 10am, I cant wait.

For more information about this code Google "Fault Code P0421" You'll get tons of information Last edited by Swankzer; Jun 2, 2008 at 12:31 PM.

P0031 - most likely pointing to a failed O2 sensor (bank 1 sensor 1 is located before the catalytic converter)

P0421 - failed catalytic converter or a failed O2 sensor

P1512 - intake manifold shutter valve is stuck - may be caused by the O2 sensor, but may not

I recommend replacing your O2 sensor first and see what happens

P0304 is Misfire in cyl# 4. Check your ignition system and fuel system.

P0421 is Catilist effeciency. Fix P0304, if P0421 returns you will need a catalitic converter

P0455 is an Evaportive emission leak. Be sure you gas cap is tight and secure. If it is ok, then there is a leak in the system.

Hi,

So you have a P0421.

A code P0421 may mean that one or more of the following has happened:

• The catalytic converter is no longer functioning properly
• An oxygen sensor is not reading (functioning) properly
• A sparkplug is fouled up

As far as running conditions if it performs normally, you most likely need a catalytic converter. The good part of this is there shouldn't be any abnormal running conditions, so it should be fine unless the engine is running very rich for some reason. (it will usually smell badly when this happens) However, on rare occasions the cat can get hot and melt down causing an exhaust restriction..bad gas mileage, low power, and possible fire potential, but most likely this is not the case. (this is generally speaking here and covering all the bases... )

The most common thing with P0421 that the fuel injection computer detects that the cat is not performing to federal specs an need to be replaced. You will need to have it fixed before your vehicle inspection.
Good luck and I hoped this helped you.