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Is it possible to get a P0421 code from the OBD computer when the engine light is not on?

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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.

Posted on May 06, 2014

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Posted on Jan 02, 2017

  • 14 Answers

SOURCE: P0421 code on recently purchased(from dealer) 2002 RS

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.

Posted on Dec 27, 2008

  • 2 Answers

SOURCE: fault code P0421

Aicux...I had the same problem with a Mitsubishi Montero Sport. The code refers to Warm up Catalytic Converter below threshold (Bank 1) which means the two oxygen sensors before and after the cat closest to the engine are showing a variance that is outside specifications. Bank 1 is on the side of cylinder 1.

I researched and found a cause that was NOT in the list of the usual causes. Generally, this code can be caused by the following:

1 Catalytic converter defective
2 Engine Misfire or similar
3 Large vacuum leak
4 Engine oil leakage into exhaust -valve guide seals, piston rings


I have learned to always look for the simplest solution before paying big bucks for things like catalytic converters, oxygen sensors, etc. I discovered my passengers side manifold was cracked. Took off the heat shield and could see the black residue from exhaust escaping the crack. Got a used manifold from partshotlines.com for $65 and installed it. Reset the code with my OBD-II device and code hasn't returned! Problem solved.

Not sure if this is what's wrong with your, but suggest you chek the simply stuff first. Good luck.



Posted on Sep 26, 2008

dealt_soul
  • 296 Answers

SOURCE: engine code p0421

Catalyst System Efficiency Below Threshold (Bank 1)

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

A code P0420 may mean that one or more of the following has happened:

* Leaded fuel was used where unleaded was called for
* An oxygen sensor is not reading (functioning) properly
* The engine coolant temperature sensor is not working properly
* Damaged or leaking exhaust manifold
/ catalytic converter / exhaust pipe
* Retarded spark timing
* The oxygen sensors in front and behind the converter are reporting too similar of readings


To Do list

* Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
* Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
* Inspect the downstream heated oxygen sensor (HO2), replace if necessary
* Replace the catalytic converter

Posted on Jan 19, 2009

  • 490 Answers

SOURCE: P0421, P0300 OBD II codes how to fix

go to this site it has all the info you need (www.obd-codes.com/p0421) or put p0300 on the end for the other code, but basically the first code means your catalytic converter is not working properly (not a big deal) and the second code means you had a random misfire in the engine, the site i gave explains all and tells you how to fix the problem hope i helped

Posted on Oct 27, 2009

  • 1 Answer

SOURCE: Mazda MPV 2003, Engine light on, code P0421 - warm

could anyone please help me with this problem that i have with my 2001 mazda protege es 2.0. i have a bad catalyst converter and im waiting for the converter to come in, but before the guys that are fixing on my car relize that i need a converter they put a egr valve and a o2 senor and when the car idle some time it will just die one me. could someone tell me what is going on.

Posted on Dec 24, 2010

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How do I replace my warm-up cat. on bank 1 for a 0421 code on my Montero sport 2001


Take it to a qualified repair shop . You don't have the tools to do the job .
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

Read more at: https://www.obd-codes.com/p0421
Copyright OBD-Codes.com

http://www.engine-codes.com/p0421_mitsubishi.html

Jun 17, 2017 | Cars & Trucks

2 Answers

P0421 CODES AND C1201


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.

Apr 24, 2014 | Toyota Avensis Cars & Trucks

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My check engine light is on and has a 421 error code? What does this mean?


OBD Code P0421refers to
Basically this means that the oxygen sensor downstream of the catalytic converter on bank 1 is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.
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

Jul 21, 2011 | 2006 Porsche Cayenne

1 Answer

P0421, P0300 OBD II codes how to fix


go to this site it has all the info you need (www.obd-codes.com/p0421) or put p0300 on the end for the other code, but basically the first code means your catalytic converter is not working properly (not a big deal) and the second code means you had a random misfire in the engine, the site i gave explains all and tells you how to fix the problem hope i helped

Oct 27, 2009 | 2001 Mazda Protege

1 Answer

I have a 1996 Mazda 626, the check engine light came on and the car has been redlining the the temp gauge. I got the engine codes which are: p0117 and p0421. Does anyone know how to solve this problem?...


The cooling fan must run or the car must be running into the wind to keep from cooking the engine. Physically turn the fan to see if it turns freely (cold engine). The computer reads coolant temperature and trips the fan relay on when normal temperature is reached. You need to read the control voltage at the relay to determine the problem. Possible bad temp sensor.

Jul 15, 2009 | 2000 Mazda 626

1 Answer

P0421 code on recently purchased(from dealer) 2002 RS


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.

Dec 27, 2008 | Mitsubishi Eclipse Cars & Trucks

1 Answer

Fault code P0421


Aicux...I had the same problem with a Mitsubishi Montero Sport. The code refers to Warm up Catalytic Converter below threshold (Bank 1) which means the two oxygen sensors before and after the cat closest to the engine are showing a variance that is outside specifications. Bank 1 is on the side of cylinder 1.

I researched and found a cause that was NOT in the list of the usual causes. Generally, this code can be caused by the following:

1 Catalytic converter defective
2 Engine Misfire or similar
3 Large vacuum leak
4 Engine oil leakage into exhaust -valve guide seals, piston rings


I have learned to always look for the simplest solution before paying big bucks for things like catalytic converters, oxygen sensors, etc. I discovered my passengers side manifold was cracked. Took off the heat shield and could see the black residue from exhaust escaping the crack. Got a used manifold from partshotlines.com for $65 and installed it. Reset the code with my OBD-II device and code hasn't returned! Problem solved.

Not sure if this is what's wrong with your, but suggest you chek the simply stuff first. Good luck.



Sep 05, 2008 | 2000 Mazda MPV

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