Subaru p0420 - P0420 Subaru Catalyst System Efficiency Below Threshold Bank 1. As the code description implies the P0421 Subaru 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 ...

 
J. Jdave Discussion starter. 7 posts · Joined 2017. #11 · Sep 11, 2019. A code P0420 may mean that one or more of the following has happened: Leaded fuel was used where unleaded was called for (unlikely) A damaged or failed oxygen / O2 sensor Downstream oxygen sensor (HO2S) wiring damaged or connected improperly.. Ok chinese oak hill wv

P0420 code is the rear sensor reading the O2 levels coming out of the cat are higher than what should be. (possible failing Cat) good sensor. P0136 is the computer reading a problem with the sensor. Just did a PO136 on a ladies 2001 Forester. Changed rear sensor for $124 for part from Subaru and 20 minutes labor.One of my favorite threads for this is the $5 fix :wink: When you get the P0420 CEL code, the cause can be: A faulty or failing front O2 sensor (if your gas mileage has dropped off with hesitation, backfires & an overly sooty exhaust tip). An exhaust air leak ahead of the rear O2 sensor (rusted or cracked pipe). A failed CAT.The "official" fixes for a P0420 code are: replace the rear O2 sensor, replace the front O2 sensor and replace the cats. - Replacing the rear O2 sensor will accomplish nothing, IMHO - Replacing the front sensor is a good idea, since it is responsible for running the engine properly. Sadly, it probably won't solve the P0420 code issue.Jan 5, 2009 · the most common problem for P0420 seems to be a bad O2 sensor. front O2 sensor needs to be OEM at about $100, rear O2 sensor can be parts store brand >$100. I also replaced my sticking EGR valve when i replace my front O2, dont know if that had anything to do with P0420. now it could also be a leak in the exhaust, replacing the gaskets seems to ... The P0420 on my car was caused by a misfire. Several have been caused by O2 sensors or MAF sensors failing. Cardoc has a pinned post about the issue. P0420 Diagnosis ... Subaru Outback 2.5L Front Catalytic Converter 2013 TO 2014. Front Catalytic Converter Direct Fit. The pipe constructed from 14 gauge tubing, with original OE style …We did a comparison to help you save as much as possible when shipping a package. Here are the cheapest ways to ship a package! Home Save Money Do you have a small business with a...2012 Forester 2.5X Manual 5spd - 142,309 miles. I bought the car in July 2021 with 116,000 miles. About 8/10 months ago or so, a P0420 code popped up, I did nothing about it for awhile since the car seemed to be running fine. Then a few months ago the car stalled as I was exiting the highway approaching the stop light at the end of the exit ramp.In this video, we're going to show you a quick and easy way to fix your P0420 without having to replace your catalytic converter. This is a quick and easy fi...Here's how to bypass or trick the O2 sensor into thinking your catalytic converter is working when you have the P0420/P0430 check engine light code. May or m...This week Dana is working on correcting the issue of Code P0420, a Bad Catalytic Converter. We started this project off with a Dorman aftermarket catalytic c...This subheading will provide a brief overview of other common Subaru diagnostic codes, their meaning, and potential fixes. Some other common Subaru diagnostic codes include P0420 (Catalyst System Efficiency Below Threshold), P1449 (Evaporative Emission Control System Vent Valve Function Problem), and U0073 …French prosecutors are looking into claims the Bolloré Group offered cheap communications services to the presidents of Togo and Guinea in exchange for contracts. France is investi...P0420 Subaru Catalyst System Efficiency Below Threshold Bank 1. As the code description implies the P0421 Subaru 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 ...In this video, you'll learn the causes and solutions of the P0420 code. The causes of the P0420 code are a bad catalytic converter, an ECM update, an exhaust...The most common fix for P0420 in the Subaru Impreza is a new catalytic converter, followed by an O2 sensor replacement. Before taking your Impreza into an exhaust shop for an (expensive) new catalytic converter, let’s ensure that’s what you need. Here’s a good P0420 diagnostic order for the Subaru Impreza: 1. Check for Other Codes.The car is a 2005 Outback 3.0R with 130000 Km on it. That minor rant aside, the CEL popped up recently (following my wife running out of gas) and the code was a P0420 catalytic inefficiency. Did my reading on this forum and did the following: - Checked exhaust for leaks. - Replaced PCV. - Replaced air filter.All O2 sensor and cat-related (P0420, P015A, P015B). It was the weekend, so I didn't go straight to the dealership, and then they went away after 5 cycles or so. ... Subaru definitely has some issues with the DI engines. My '04 FXT never had much of a problem with carbon buildup, though I did SeaFoam it myself a few times once it got up …double check battery connections. catch-up on any any postponed maintenance. the P0420 often is due to something unrelated to the cat conv so, that should be the last thing you suspect. Exhaust leaks, vacuum leaks, weak spark.... Time Flies Like an Arrow, Fruit Flies Like a Banana! Hans747. Like.The numbers: Ugly, as expected. Credit Suisse reported a second-quarter loss of 700 million Swiss francs ($779 million), its worst quarterly result since the depths of the financia...This will fix a P0420 code most, if not all of the time. Also have a look at this thread: $5 fix ~ Silke ~ '02 Forester S 5MT - "Cooper" '11 Honda CR-Z 6MT - "Kat" ... We’re the best Subaru Forester Owners Forum to talk about the best years of the Subaru Forester, modifications and reliability history of the Subaru Forester.If you've cleaned your MAP, then all that's left is the rear O2 sensor and the cat itself. Dealers change rear O2 sensors . . . mostly because that's one of the few pieces left in the puzzle. Then comes the cat . . . chi-ching! Honestly, I think Subaru uses the P0420 to increase dealer repair traffic.P0420 Subaru Code - Catalyst System Efficiency Below Threshold. How to Fix. Check the 'Possible Causes' listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, …Code P0420 Description. The Engine Control Module (ECM) uses sensors mounted in front of and behind the Three-Way Catalytic Converter (TWC) to monitor its efficiency. The first sensor, the air-fuel ratio sensor, sends pre-catalyst information to the ECM. The second sensor, the heated oxygen sensor, sends post-catalyst information to the ECM.May 31, 2012 · 16442 posts · Joined 2015. #24 · Feb 24, 2017. Alright for future people who find this p0420 is a catalyst failure. You either need to replace the cat, replace the sensor if the cat is good, or ideally have the proper tune on the car so it blocks the code. Sent from my SAMSUNG-SM-G935A using Tapatalk. Over at DonkeyMagic you'll find a nifty Web-based form that'll help create the code you need to add a Google Map to your site. Over at DonkeyMagic you'll find a nifty Web-based for...Here's an Amazon link to that impact gun → http://www.amazon.com/gp/product/B00BWFIKZO/ref=as_li_qf_sp_asin_il_tl?ie=UTF8&camp=1789&creative=9325&creativeASI...If you are a car owner, it is likely that you have encountered the dreaded check engine light at some point. One of the most common trouble codes that many drivers come across is c...P0420: význam, příčiny, opravy. Význam kódu P0420. Chybový kód P0420 indikuje, že katalyzátor nepracuje účinně, a obvykle i to, že je nutné ho vyměnit. Pokud se objeví, nutné bude provést diagnostiku motoru, a diagnostiku systému vstřikování paliva, zapalování, a výfukového systému. Příčiny P0420.Has your check engine light recently turned on? Are you seeing the dreaded error code P0420 on your vehicle’s diagnostic scanner? Don’t panic just yet. Code P0420 is a common issue...NinoS. 1104 posts · Joined 2014. #3 · Sep 8, 2020. I've used them before back when I put headers on my 03X - the fix works. You'll want to take a look at your 02 sensor and make sure you have space for a spacer (or maybe even if you can get it out), might need a 90 degree spacer (i'm not familiar with the SH forester).In 2021, I had a lot of fun working to track down a P0420 code. As a result of this, I found several other issues with my 2016 WRX (manual transmission), and fixed them. The following have been successfully done: Full engine rebuild (new pistons, bearings, gaskets.... the works) - No mechanical issues. No fluid leaks of any kind.December 27, 2022. Advertiser Disclosure. TABLE OF CONTENTS. Fix your check engine light yourself. GET FIXD. What Does Code P0420 Mean? P0420 definition : Catalyst … It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may be slightly different depending on the model. So this engine code article applies to Nissan, Toyota, Chevrolet, Ford, Honda, GMC, Subaru, VW, etc. P0420 is one of the more common trouble codes that we see. 8 posts · Joined 2019. #1 · Aug 25, 2019. Hey guys I just picked up my 04 Forester a few weeks ago as my first car and I love the car so much already but I recently just had my Check Engine Light pop up. Ran the code and got " P0420 - Catalyst System Efficiency Below Threshold Bank 1". I did some research and I'm pretty positive one of my o2 ...The OBD2 code P0420 is stored in memory when the PCM detects a low efficiency in the catalyst system. What symptoms may occur with this OBD II code? Usually, the only symptom is the CEL lit. The Check Engine Light will turn on after few driving cycles to alert the driver about the situation. But under some circumstances, the CEL will blink ...P0420: význam, příčiny, opravy. Význam kódu P0420. Chybový kód P0420 indikuje, že katalyzátor nepracuje účinně, a obvykle i to, že je nutné ho vyměnit. Pokud se objeví, nutné bude provést diagnostiku motoru, a diagnostiku systému vstřikování paliva, zapalování, a výfukového systému. Příčiny P0420.The most common fix for P0420 in the Subaru WRX is a new catalytic converter, followed by an O2 sensor replacement. Before taking your WRX into an exhaust shop for an (expensive) new catalytic converter, let’s ensure that’s what you need. Here’s a good P0420 diagnostic order for the Subaru WRX: 1. Check for Other Codes.The most common fix for P0420 in the Subaru Baja is a new catalytic converter, followed by an O2 sensor replacement. Before taking your Baja into an exhaust shop for an (expensive) new catalytic converter, let’s ensure that’s what you need. Here’s a good P0420 diagnostic order for the Subaru Baja: 1. Check for Other Codes.2009 - P0600 and P0420 - Updated! 2009 2.5 4EAT, Premium, 135000 miles. Ive been getting a P0420 for the last year. Even after a new exhaust was installed, including new sensors. Sadly, for me, I just reset the code each time it occurs as the car generally runs "OK". I drive about 70 miles each day (35 miles each way) for a commute …Generally P0420 code can be set by exhaust leaks, bad O2 sensor or a bad cat. P0420 definately seems to be a common occurrance with some Subaru's. PZEV might have more. and I was reading those PZEV 2005-2009 cars also race their engines on first cold up, to heat the cats up fast and to stop the stink. (like H6 ones do).Jan 6, 2024 · P0420 Code in Subaru The P0420 code on a Subaru often can be triggered by a bad catalytic converter or a faulty oxygen sensor on older models. Look for exhaust leaks as well, as with Honda, replacing your catalytic converter or oxygen sensors and regular servicing can help resolve the issue. 2009 Subaru Outback P0420. It was diving awesome with no sign of issue when I got a CEL and my cruise and stability control lights came on and the systems disabled. This happened on the way home from purchasing the car. No sign of issues on my test drive Tested the code and it showed P0420.Subaru Liberty P0420 OBDII Code Defined. P0420 is a OBDII trouble code. The code technically stands for: Catalyst System Efficiency Below Threshold. Your Liberty has at least two oxygen sensors, one before and after the catalytic converter. Among the many jobs that oxygen sensors have is they have to measure the emissions levels coming in and ...M. mudd123 Discussion starter. 15 posts · Joined 2014. #1 · Feb 5, 2015. My 2003 OB w/ 2.5 135k developed P0420 code back in August. I have been playing around with it for awhile trying to figure it out. Here is the background on what took place: The CEL came on on a HOT and HUMID day while going about 60 mph, and about 1/8 of a tank of fuel.My 2013 Subaru XV crosstrek was giving me the code p0420, it was kicking out my stability control at the same time. In this video I replace my exhaust manifo...Here are the most common causes of P0420 in the Subaru Forester: Likely Causes. Bad catalytic converter; Bad O2 sensor; Other Causes. Exhaust leak; O2 …This will fix a P0420 code most, if not all of the time. Also have a look at this thread: $5 fix ~ Silke ~ '02 Forester S 5MT - "Cooper" '11 Honda CR-Z 6MT - "Kat" ... We’re the best Subaru Forester Owners Forum to talk about the best years of the Subaru Forester, modifications and reliability history of the Subaru Forester.P0420. I have a 2004 Legacy 2.5 California spec (3 cats, 5 O2 sensors) with a recurring p0420 pending code on bank 1 that keeps popping up on my blue driver for the past 2000 miles. The cats were replaced under warranty about 8-9 years, 100,000 miles ago. The Oxygen sensors are all original, so they have 167,000 miles on them.Subaru Tribeca P0420 OBDII Code Defined. P0420 is generic (has the same meaning for all vehicles made in 1996+) OBDII trouble code. Here’s the technical …The P0420 code in a Subaru Outback will often be thrown if one of your car’s oxygen sensors is not functioning correctly. There are rarely drivability issues associated with P0420. For most people, the first sign that anything is wrong is the service engine soon light coming on. El código de diagnóstico P0420 de Subaru, también conocido como DTC P0420, se refiere a un problema en el convertidor catalítico de tres vías del vehículo. Este código se activa cuando el Módulo de Control del Motor (ECM) detecta que la relación de frecuencia de cambio de los sensores de oxígeno calentados 1 (sensor O2 delantero) y 2 ... Replaced the spark plugs, new spark plugs wire. Tried the anti-fouler, first using 1 then using 2, that made it worst, throw me 3 more codes P2096 and P2098, and …P0420 is VERY RARELY a failing cat. It is most commonly a failing oxygen sensor (front Subaru, rear any brand), vacuum leak, exhaust leak or what not. Search that code on the forums and you'll find plenty of info. Cats rarely fail without serious mechanical problems, I think your mechanic wants to give you an expensive repair bill.21417 posts · Joined 2006. #5 · Jul 10, 2014. However, when the light is cleared, while using the cruise control there is a slight hesitation present ONLY while the cruise is being used. There is no hesitation or issue present otherwise. It's possible that the P0420 and the hesitation are related, and that the hesitation is more noticeable ...The Continental ContiProContact tire is the best overall tire for the 2015 Subaru Forester as of March 2015, according to tire review site BestReviews.com. The site also recommends...This will fix a P0420 code most, if not all of the time. Also have a look at this thread: $5 fix ~ Silke ~ '02 Forester S 5MT - "Cooper" '11 Honda CR-Z 6MT - "Kat" ... We’re the best Subaru Forester Owners Forum to talk about the best years of the Subaru Forester, modifications and reliability history of the Subaru Forester.Forester 2001 L - Stock 101k Miles P0420 - Catalytic Converter Efficiency Below Threshold The forester has been throwing this code for a few months now, typically shows up on long highway runs (but to be fair, that is the vast majority of my driving).P0420 please please help me. Jump to Latest Follow ... I’ve got a 2004 Subaru Outback Base model. 69840 miles, got it in July of 21 from my grandfather. I’ve done routine maintenance and some preventative stuff over the yearsJan 29, 2024 · The P0420 code in a Subaru Outback is typically triggered by issues related to the vehicle’s catalytic converter. One common cause is a faulty or damaged catalytic converter, which may be clogged or no longer functioning properly. Another possible cause is an oxygen sensor failure, specifically the downstream oxygen sensor, which measures the ... It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may be slightly different depending on the model. So this engine code article applies to Nissan, Toyota, Chevrolet, Ford, Honda, GMC, Subaru, VW, etc. P0420 is one of the more common trouble codes that we see. If the check engine light comes on in your Subaru there is always a corresponding code set in the computers memory. You can …Only do this on a stone cold motor. Once it pops loose remove the pipe then the socket and from below the car put the socket wrench back on the sensor and back it the rest of the way out. Install the new one from below. Currently the OEM o2 sensor is available various places for between 100 to 140 dollars.Subaru code P0420 refers to a diagnostic trouble code that indicates an issue with the catalytic converter in a Subaru vehicle. It means that there is a …Jul 9, 2014 · 21417 posts · Joined 2006. #5 · Jul 10, 2014. However, when the light is cleared, while using the cruise control there is a slight hesitation present ONLY while the cruise is being used. There is no hesitation or issue present otherwise. It's possible that the P0420 and the hesitation are related, and that the hesitation is more noticeable ... This Subaru Outback has a P0420 Again! This catalytic converter was replaced two and a half years ago and the light is on again for catalytic converter ineff...NinoS. 1104 posts · Joined 2014. #3 · Sep 8, 2020. I've used them before back when I put headers on my 03X - the fix works. You'll want to take a look at your 02 sensor and make sure you have space for a spacer (or maybe even if you can get it out), might need a 90 degree spacer (i'm not familiar with the SH forester).The P0420 Diagnostic Trouble Code is a clear indication that your vehicle's catalytic converter is not efficiently functioning. The Catalytic Converter is part of the …Feb 20, 2015 · The "official" fixes for a P0420 code are: replace the rear O2 sensor, replace the front O2 sensor and replace the cats. - Replacing the rear O2 sensor will accomplish nothing, IMHO - Replacing the front sensor is a good idea, since it is responsible for running the engine properly. Sadly, it probably won't solve the P0420 code issue. There is a thread on this forum with over 3,000 posts that deals specifically with the P0420 code. The main thing to know is that this code DOES NOT mean the CAT needs replacing. The next thing to know is that the O2 sensors need to be genuine Subaru or Denso brand as other sensors such as Bosch react too slowly for the ECU.One of my favorite threads for this is the $5 fix :wink: When you get the P0420 CEL code, the cause can be: A faulty or failing front O2 sensor (if your gas mileage has dropped off with hesitation, backfires & an overly sooty exhaust tip). An exhaust air leak ahead of the rear O2 sensor (rusted or cracked pipe). A failed CAT.NinoS. 1104 posts · Joined 2014. #3 · Sep 8, 2020. I've used them before back when I put headers on my 03X - the fix works. You'll want to take a look at your 02 sensor and make sure you have space for a spacer (or maybe even if you can get it out), might need a 90 degree spacer (i'm not familiar with the SH forester).The connection to your P0420 isn't an obvious one (at least to me). Typically the problems associated with a bad PCV valve is that you end up with a mildly pressurized crankcase rather than one below atmosphere, and you push oil out from your valve cover gaskets or spark plug tubes. '19 Forester Premium, '18 Forester Limited, '15 Toyota …Most common causes for the P0420 code: failing oxygen sensor, exhaust leak, cat. failure. The first two are much more common and much easier to fix. If these don't fix it, then look at the cat. 2002 Outback wagon 3.0 L.L. Bean no more: " Mal ". 142,000 and counting. Mismatched cloth interior swap.As the code description implies the P0420 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).This subheading will provide a brief overview of other common Subaru diagnostic codes, their meaning, and potential fixes. Some other common Subaru diagnostic codes include P0420 (Catalyst System Efficiency Below Threshold), P1449 (Evaporative Emission Control System Vent Valve Function Problem), and U0073 …Looking for a Subaru dealer? With over 20 dealerships across the country, you can discover one near you and find the model that fits perfectly into your world.Chapter/Region: NESIC. Location: Lake George , New York. Vehicle: 2021 WRX BASE. Pure Red. Code P0420 and P0137 after Invidia Catted J pipe install on 2021 wrx. So , last month I installed my Invidia catted j pipe and with it the Cobb stage 2+ big sf intake on my 2021 WRX 6-MT . I also have a remark mid pipe and axle back muffler …P0420, catalytic converter, and rattle noise. Just purchased a 2002 Outback 2.5L, 4 cylinder, 4 Door sedan with 140,000 miles. After a couple of weeks the check engine light came on and the P0420 code was the diagnosis. After reading other post it appears I should replace the 02 sensors and see if that fixes the problem.Ah the classic Subaru P0420. So are parts required to fix this pesky emissions code? In this case we get a good example of where the "money light" gets its n...The P0420 code will not likely be caused by, or cleared by removing and replacing, the gas cap. The gas cap could be faulty, and is causing the warning lights to come on for some other code, but it's not the P0420. Just because at one time the lights came on and code then was a P0420, doesn't mean that every time the lights come on, …In this video I am working on a 2014 Subaru Outback with a 2.5 and CVT. We have done quite a bit of work to this car to solve an ongoing P0420 code. Make su...I have the dreaded P0420 code. It is intermittent. Base engine. No turbo. Just purchased this 2006 outback with 145k miles. Has a brand new cat and new front 02 sensor. ... Subaru runs a wideband O2 in the front. The 0-1v readout that most other cars have, does not apply to Subaru. The rear O2s are the standard 0-1v units.It's a lot to digest, but I highly recommend clicking on this P0420 thread started by Cardoc over on the Outback forum. Cardoc and Plain OM are the primary gurus and are both still active there. Tons of good info. In the first 70 or more pages (1400+ posts), there are many references to Romraider software to get OBD data.Catalytic converters don't last forever. In this video, we diagnose a P0420 on a Toyota Camry with over 330,000 miles! Enjoy!

In this video, we're going to show you a quick and easy way to fix your P0420 without having to replace your catalytic converter. This is a quick and easy fi.... Bre selling sunset before

subaru p0420

This code simply means that somewhere in the chain of events that controls the overall performance of the engine there is a problem and you have to find it. List of …2013 Outback P0420 code. Hello, I am new to this forum and Subarus meaning that this is my first Subaru and first post. Thanks for all the great information. I currently have a P0420 code and am trying to determine the issue. I have a 2013 Outback with 121k miles which I bought back in March 2017. There were lean codes which were …Hi all, I've been chasing a P0420 code on my base 2007 outback (to prevent the CEL from coming on so my cruise will work). Check engine light first came on with P0420 after about a hundred miles. ... Our converter manifold is compatible with the2005-2010 Subaru and 2006 Saab 9-2X 2.5L, helpful in upgrading the exhaust system to …Air can and does enter cracks or small holes in the exhaust. A system in good shape does not have measurable pressure in it. The exhaust flowing through the pipe can draw ambient air in through openings. A partially blocked converter won't necessarily throw a P0420 code if it is still working as a catalyst.Check Engine Light and P0420 and P0430 Codes. So, your Check Engine light is on, and you’ve got either a P0420 or P0430 code, on your OBD-II scanner. This “Catalyst system efficiency below threshold” code is triggered when your car’s computer (the powertrain or engine control module (PCM or ECM)) detects a catalytic converter …Catalytic Converter Replaced still showing P0420. I took my 2003 outback into my usual mechanic for P0420 codes and he replaced the Catalytic Converter. Check Engine light came back on only two days after, so I ran the codes and got P0420 again. I cleared them and chalked it up to the new CC needing a few days.P0420 code is the rear sensor reading the O2 levels coming out of the cat are higher than what should be. (possible failing Cat) good sensor. P0136 is the computer reading a problem with the sensor. Just did a PO136 on a ladies 2001 Forester. Changed rear sensor for $124 for part from Subaru and 20 minutes labor.Subaru WRX P0420 OBDII Code Defined. P0420 is generic (has the same meaning for all vehicles made in 1996+) OBDII trouble code. Here’s the technical …Nov 30, 2018 · P0420 Diagnosis: Subaru Tribeca. The most common fix for P0420 in the Subaru Tribeca is a new catalytic converter, followed by an O2 sensor replacement. Before taking your Tribeca into an exhaust shop for an (expensive) new catalytic converter, let’s ensure that’s what you need. Here’s a good P0420 diagnostic order for the Subaru Tribeca: 1. Here's how to modify your car's oxygen sensor to get rid of a P0420 OBDII code, clear the check engine light and pass an emissions test.The P0420 code is thr...Welcome to the Subaru Outback Owners Forum, we have tons of information about your Subaru Outback, from a Subaru Outback Wiki to customer reviews. Show Less . Full Forum Listing. Explore Our Forums. Gen 5: 2015-2019 Problems & DIY Maintenance Gen 4: 2010-2014 Gen 6: 2020-present General Discussions.My 09 Forester has around 130k on it and over the past few weeks I've had some issues with a P0420 code. I have a persistent code reader and have gotten that. I've cleared the code a few times and it comes back after 30 or so miles. I've also put in a bottle of Cata-Clean to help un-gunk the converter. Additional symptoms are, engine knocking ...There is a thread on this forum with over 3,000 posts that deals specifically with the P0420 code. The main thing to know is that this code DOES NOT mean the CAT needs replacing. The next thing to know is that the O2 sensors need to be genuine Subaru or Denso brand as other sensors such as Bosch react too slowly for the ECU.The P0420 code signals a low catalyst system efficiency. This code suggests that the oxygen levels are below the desired threshold (Bank 1), which most often results from problems with your car ...P0420 is a sign the o2 and air fuel sensors are functioning and they are monitoring the catalyst properly. The EASIEST way to tell if a catalyst is worn is the smell of raw fuel from the exhaust. Confirmation is difficult without a graphing scan tool, I graph the front o2 to the back and watch the rear o2 sensors activity in comparison to the ....

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