Subaru p0420

This is a very common Subaru code. It ranges from seemingly "unfixable" (i.e., reflash the ECU to ignore it), catalytic converter replacement, rear O2 sensor, exhaust leak, all kinds of stuff. I wouldn't worry too much unless other symptoms/codes appear. My car throws a P0420 about every 1000-2000 miles (edit: and still gets high 20's average ...

Subaru p0420. Subaru’s Lineartronic CVT design uses a chain rather than a cable to join the two pulleys of the CVT system as in most other CVT designs.

Apr 9, 2017 · 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.

=====Claim your FREE engine code eraser 👉 https://free.nonda.co 👈=====Engine Code SUBARU P0457 Saving Repa...Just over a month ago my 2013 Outback engine light came on showing a p0420 code along with the a blinking emergency brake light as well as a blinking cruise control icon. I cleared the code and everything on the dash went back to normal. The car had been struggling to start, pair the slow starts with the new p0420 code and I was starting to get ...If you’re an avid DIYer and a car enthusiast, you may have come across the dreaded “Code P0420” at some point. This diagnostic trouble code is related to your vehicle’s catalytic c...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.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 P0420 is a finicky code. There is a range of "acceptable" parameters that Subaru has set. If the O2 sensor sees a value that is outside of that range, even for just a fraction of a second, you get the P0420. Adding the extension doesn't stop the O2 sensor from working, it just doesn't get the immediate read, but more of a mixed read.The P0420 set the CEL AND made the cruise contrl light blink. The Cel is obvious as to why it was on. The P0420 did that. Now the blinking cruise, On Subaru's with 'drive-by-wire' the cruise control is integrated into the ECU, but is a seperate co-processor. If it detects any engine faults that will cause it to malfuction, it will disable ...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 malfunction in the efficiency of the catalytic converter, which could be caused by various factors such as a faulty oxygen sensor or an exhaust leak. This code should be addressed promptly as ...

Ran my OBD2 scanner and turns out I have a catalytic converter code failing code (P0420). I remember this happening to me about 4-5 years ago but all I did was clear the code and i’m pretty sure it never came back until very recently. So I cleared the code just like I did 4-5 years ago and within maybe 2 weeks the code came back again. Jan 10, 2012 · 63 posts · Joined 2011. #1 · Jan 10, 2012. I have a 2004 OBW and it keeps throwing the P0420 catalytic system below threshold code. The car is bone stock. It is drive by wire and has the California emissions on it. It's engine is a model EJ259 if I remember correct. I've tried using the anti-foulers, and even the electronic fixes in the rear ... After a night in Nelson, we arrived in Revi for a few bluebird days following a 30-day storm cycle. HITTING THE OPEN ROAD, loaded to the gills with gear, plans to live in a truck c...104 posts · Joined 2008. #2 · Oct 3, 2011. I as well have been dealing with the P0420 and a local subie dealer out here mentioned basically to clear the code and see how long it takes for it to come back up. Meanwhile, run fuel cleaner through the system to clear up the injectors and the 02 sensors. You said your putting the anti-foulers on ...May 23, 2011 · 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. P0420 Hard to start Help! 2002 Forester L. 136k Manual transmission. Bought this car about a month ago (first subaru) about a week into owning the car it developed a small intermittent start issue. Basically when the engine is WARM it will crank 2-3 times then misfire. Turning the key off then back on it almost always cranks once and …From a little Googling, it seems the P0420 code means the exhaust is rich at the O2 sensor after the catalytic converter. Following that scenario, I would pursue the following possible causes: 1) The O2 sensor is malfunctioning. Nowadays, 100k miles is considered the life of an O2 sensor, and you're well beyond that.JENNISON GROWTH EQUITY FUND 6- Performance charts including intraday, historical charts and prices and keydata. Indices Commodities Currencies Stocks

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. The gaming industry is just one example of an industry squeezed by regulation. South Africa’s uncertain digital regulatory environment may deter investors and tech entrepreneurs, d...Jan 14, 2022 · That's one of Subaru's plans to make you fix your car instead of ignoring the code. In my experience the P0420 code has always been fixed (4 times on three different cars, and the second time on one car was the other bank on a 3.6R) by replacing the downstream O2 sensor. Did you replace it with a good brand-name sensor or whatever you found ... 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 …

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Tel: 01293 429800. Subaru UK's range of all-wheel drive SUV and family cars including the brand new Solterra and XV models. Discover the Subaru that fits into your world.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 ...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 …After a night in Nelson, we arrived in Revi for a few bluebird days following a 30-day storm cycle. HITTING THE OPEN ROAD, loaded to the gills with gear, plans to live in a truck c...

Jan 10, 2012 · 63 posts · Joined 2011. #1 · Jan 10, 2012. I have a 2004 OBW and it keeps throwing the P0420 catalytic system below threshold code. The car is bone stock. It is drive by wire and has the California emissions on it. It's engine is a model EJ259 if I remember correct. I've tried using the anti-foulers, and even the electronic fixes in the rear ... 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.The most common cause of the P0420 engine code is a degraded catalyst. Catalytic converters/catalysts break down over time and can also become clogged. Cylinder misfires will significantly reduce ...45837 posts · Joined 2007. #2 · May 17, 2020. @Jaime ochoa welcome to the forum from Oregon! The P0420 CEL code is from the rear O2 sensor, but that doesn't mean the sensor is bad. The rear O2 sensor is monitoring for excess 02 in the exhaust flow, so the fault could be something upstream... even a pinhole leak in the exhaust pipe?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 …The P0420 code is a common issue that many Subaru Impreza owners experience. This subheading aims to provide a detailed explanation of what the code means and its implications for the vehicle. The P0420 code signifies a problem with the catalytic converter efficiency in the exhaust system of the Subaru Impreza.Eight hours a day is way too much at some Swedish companies. By clicking "TRY IT", I agree to receive newsletters and promotions from Money and its partners. I agree to Money's Ter...My '11 (140k miles) has been throwing a P0420 code along with running a bit rough, it stalls from a start (oddly the autostart has no issues keeping it running), and I'd say I'm down to about 70% power overall. ... We’re the best Subaru Forester Owners Forum to talk about the best years of the Subaru Forester, modifications and reliability ...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...

There are several potential causes for Subaru code P0420, including a faulty catalytic converter, oxygen sensor malfunction, exhaust leaks, engine misfires, or issues with the fuel system. It is important to diagnose the specific cause accurately to determine the appropriate course of action.

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.Mar 25, 2010 · 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. 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 ...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.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 …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).I'm thinking it definately needs a tune up and some other minor maintenance. An issue I had planned on tackling as things started settling down for me here soon. However, yesterday as I was driving, the CEL came on in conjunction w/ the CRUISE caution light. Went to autozone, and got the P0420 code.Subaru manufactures its cars in two factories, one located in Japan and the other in the United States. Only the Impreza, Legacy sedan, Tribeca, and Outback are produced in the Uni...

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I'm thinking it definately needs a tune up and some other minor maintenance. An issue I had planned on tackling as things started settling down for me here soon. However, yesterday as I was driving, the CEL came on in conjunction w/ the CRUISE caution light. Went to autozone, and got the P0420 code.Tech Notes. As the code description implies, the P0420 code means that the vehicle's Engine Control Module (ECM) has detected that the Three-way Catalyst Converter is not working properly (it is not as efficient as the factory expects). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases, the Three-way Catalyst ...B. bdubbs84 Discussion starter. 13 posts · Joined 2008. #7 · Oct 20, 2008 (Edited) Well, I got rid of the P0420 catalyst code, but now I have two new codes. One is P0440 (Evap. Emission Control System Malfunction) and the other is P0136 (O2 Sensor Circuit Malfunction, Bank 1 Sensor 2). I already have the O2 sensor spacer in place.Exhaust Leaks. An exhaust leak can cause the P0420 code by allowing excess oxygen into the exhaust stream and disrupting the catalytic converter's ability to reduce emissions. Malfunctioning EGR …There're many factors that could cause a P0420 code including among others the following: Damaged, burnt, corroded, open or shorted O2 sensor wiring. Worn, corroded, burnt, disconnected or bent O2 sensor wiring harness connector pins. Faulty or deficient downstream oxygen sensor Leak between the exhaust pipe and the …B. bdubbs84 Discussion starter. 13 posts · Joined 2008. #7 · Oct 20, 2008 (Edited) Well, I got rid of the P0420 catalyst code, but now I have two new codes. One is P0440 (Evap. Emission Control System Malfunction) and the other is P0136 (O2 Sensor Circuit Malfunction, Bank 1 Sensor 2). I already have the O2 sensor spacer in place.The CEL would turn on and off occasionally so I changed the Wires, Plugs and coil pack and went ahead and did the 2 - O2 Sensors. Now over time I have earned 2 additional codes for my efforts. I have all three, (P0301, (Cylinder 1 Misfire Detected), P0303, (Cylinder 3 Misfire Detected), & P0420, (Catalyst System Efficiency Below …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.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...The codes are there based on data received from the AF sensor, O2 sensor and Knock sensor. P0420 is Catalyst Efficiency, but since you stated it glowed, its outa there. P0303 and 304 are misfires on cylinders 3 and 4, both opposing cylinders on the backside of the engine. P0171 is system too lean bank 1, but since you only have one AF …There's some good information from that post onward. The gist of these messages and threads is this: to deal with a P0420 code on 2005+ vehicles, the ECU should be remapped to exclude this code, rather then using the $5 fix. The reasoning is that the rear O2 sensor is actually used to manage the engine, at least a little bit, rather than … ….

OBD II fault code P0420 is a generic code that is defined as “Catalyst System Efficiency Below Threshold (Bank 1)”, and is set when the PCM (Powertrain Control Module) detects a condition that indicates that the catalytic converter on Bank 1 is operating below the minimum allowable efficiency threshold. Note that on engines with two banks ...p0420 catalyst efficiency low bank 1. I have had my check engine light come on and go off several times in the past 9 months, but the last time it came on it did not go off, so I took it to aplace to find out what is the problem, so he hooks it uo to this snap on computer and read the code as p0420 catalyst efficiency bank 1, and he rests it.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 ...Visit me at: http://www.ericthecarguy.com/O2 Sensor Video: https://www.youtube.com/watch?v=NIzcztO-CCsDiscussion about this video: http://www.ericthecarguy...Tech Notes. As the code description implies, the P0420 code means that the vehicle's Engine Control Module (ECM) has detected that the Three-way Catalyst Converter is not working properly (it is not as efficient as the factory expects). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases, the Three-way Catalyst ...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 ...Eight hours a day is way too much at some Swedish companies. By clicking "TRY IT", I agree to receive newsletters and promotions from Money and its partners. I agree to Money's Ter...If the code is happening on a later model Subaru (2015 - present) the chances are it's a bad catalytic converter, otherwise a newer model would throw a specific code for the oxygen sensor if it was the culprit. P0420 Code in Toyota. If you have code P0420 in Toyota models, it's usually due to a faulty catalytic converter.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 ... Subaru p0420, Subaru of America, Inc. (SOA) has determined that vehicles affected by this Service Program require ECM reprogramming. ... performed with over 100,000 miles and the Check Engine light illuminated with DTC P0420 in the ECM memory. The catalytic converter efficiency test must also indicate replacement is necessary. For all other vehicles, the ..., OBD II fault code P0420 is a generic code that is defined as “Catalyst System Efficiency Below Threshold (Bank 1)”, and is set when the PCM (Powertrain Control Module) detects a condition that indicates that the catalytic converter on Bank 1 is operating below the minimum allowable efficiency threshold. Note that on engines with two banks ..., 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 P0420 is a finicky code. There is a range of "acceptable" parameters that Subaru has set. If the O2 sensor sees a value that is outside of that range, even for just a fraction of a second, you get the P0420. Adding the extension doesn't stop the O2 sensor from working, it just doesn't get the immediate read, but more of a mixed read., The Federal Reserve Bank of St. Louis president helped spur a plunge below the opening print and to the day's lows....IWM For several weeks the market has been rallying on news..., 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 ..., p0420 maybe a rear o2 sensor at this stage,...although other things produce it such as a a loose exhaust gasket before the last o2 sensor. p0442 and p0456 both indicate of a minor evaporative system leak,...such maybe a hose or something in the area of the gas tank and the attached evap system that has become cracked overtime. be it a …, 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 ..., How to fix you emissions p0420 code for cheap, easy, fast. Watch this video and learn how to turn off you cars check engine in under 10 minutes with parts av..., 63 posts · Joined 2011. #1 · Jan 10, 2012. I have a 2004 OBW and it keeps throwing the P0420 catalytic system below threshold code. The car is bone stock. It is drive by wire and has the California emissions on it. It's engine is a model EJ259 if I remember correct. I've tried using the anti-foulers, and even the electronic fixes in the rear ..., 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 …, The P0420 Code in a Subaru WRX usually means there's a problem with the catalyst efficiency. This means that the efficiency is below the threshold in bank 1. It's also common in other Subaru models such as Forester, Impreza, Outback, and Legacy. The check engine light comes on when the Powertrain Control Module triggers the P0420 …, 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)., 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., Dec 2, 2022 · The nerdy and keen eyed will notice I omitted the valve lash adjustment on these 2008-2010 Subaru products with the 2.5L engine...because nobody and I mean N... , P0420 Hard to start Help! 2002 Forester L. 136k Manual transmission. Bought this car about a month ago (first subaru) about a week into owning the car it developed a small intermittent start issue. Basically when the engine is WARM it will crank 2-3 times then misfire. Turning the key off then back on it almost always cranks once and …, 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 common causes of the P0420 code in Subaru vehicles include a faulty catalytic converter, oxygen sensor malfunction, exhaust leaks, engine misfire, or fuel system issues. These issues can lead to increased emissions levels, triggering the P0420 code which indicates a problem with the efficiency of the catalytic converter., How to diagnose code P0420 on a Subaru Legacy. Typically, you'll find out about P0420 because your malfunction indicator lamp or "check engine light" turned on & you or a mechanic diagnosed the problem with an OBD II code scanner like this one from Bluedriver. You may experience a very slight reduction in engine power from reduced …, The P0420 code is a common diagnostic trouble code that indicates an issue with the catalytic converter in a Subaru Forester. This code is significant as it can affect …, The six business groups of Alibaba are Cloud Intelligence Group, Taobao Tmall Commerce Group, Local Services Group, Cainiao Smart Logistics, Global Digital Commerce Group, and Digi..., 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 turned out to be a bad ignition coil. Replaced it, and the car runs and drives great. After about 50-100 miles of driving, it threw the P0420 code. (with a bunch of other dash lights like I read the subarus do). seems to run fine. I have an OBD2 adapter and Torque pro, and I did a few readings. One screenshot is idle, one is around 2k RPMS., 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., p0420 maybe a rear o2 sensor at this stage,...although other things produce it such as a a loose exhaust gasket before the last o2 sensor. p0442 and p0456 both indicate of a minor evaporative system leak,...such maybe a hose or something in the area of the gas tank and the attached evap system that has become cracked overtime. be it a …, Medicine Matters Sharing successes, challenges and daily happenings in the Department of Medicine Dr. Risha Irvin will become the next Associate Vice Chair for Diversity and Inclus..., The P0420 code usually came back with 1 to 2 years in the reviews. I rolled the dice on a middle of the road unit, and fortunately it lasted at least 3 years, and may still be good, as I no longer own the car. ... We’re the best Subaru Forester Owners Forum to talk about the best years of the Subaru Forester, modifications and reliability ..., 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 …, 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 …, I ran into a code that occurred 3 times now when driving on the freeway only at around 60-70 mph which was a P0420 code. I have been told by fellow Subaru enthusiasts in my area to replace the front O2 sensor, but read on this forum that it should be the rear sensor. On the 2011 LGT, the O2 sensors are close to each other so I really …, 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., So my wife and I bought an '07 Outback Basic back in January, used with about 130k miles on it. MIL came on around 6 weeks ago with a P0420 code. Been doing a lot of googling/reading about P0420 codes lately- I've had several conversations with different mechanics around town, some helpful and some not, but someone suggested …, P0420 Subaru: Code Meaning, Causes, Symptoms, & Tech Notes. The Engine Control Module (ECM) monitors the switching frequency ratio of heated oxygen sensors 1 (front O2 sensor) and heated oxygen sensors 2 (rear O2. www.engine-codes.com.