Subaru p0420 - P0420 Code: Causes, Meaning, Symptoms (and How to Fix it) (mechanicalboost.com) 2021 Crosstrek Limited Crystal White / Black leather. (MNRF - 33) Moonroof Package W/Nav/HK AUDIO. Auto-dim Mirror/Homelink/Compassr + Side moldings All Weather Mats. Outside mirror Auto Dim Rear Bumper Cover LED lightsDoor Edge Guards.

 
May 11, 2017 · 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 that since the only ... . Ga tag office columbus ga

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...Today we have a 2011 Subaru Outback with 174,000 miles. The check engine light is currently on and showing P0420. Does the catalytic converter need replaceme...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.GM CEO Mary Barra sees the automaker selling personal autonomous vehicles by the end of the decade by leveraging technology from its self-driving subsidiary Cruise, according to co...=====Claim your FREE engine code eraser 👉 https://free.nonda.co 👈=====Engine Code SUBARU P0457 Saving Repa... 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 ... 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...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.4 days, 1 subaru wideband sensor, and 3 drive cycles later, I have clearing subaru readiness monitors down to a T. And the wide-band that came with my AEM failsafe gauge is looks to be the same model as …Nov 30, 2018 · 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. 5784 posts · Joined 2018. #2 · Apr 12, 2023. There is a whole thread on this forum about the P0420 code, what can cause it and how to diagnose the cause. If you take the time to read the first 10 to 20 posts of that thread you may be able to diagnose the cause. The code can be caused by bad fuel, faulty O2 sensors, poor electrical …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.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.I've mentioned to the Subaru dealer that there are many causes for the P0420 code and they said they did the diagnostics to rule out the other causes and confirmed that the cat is definitely out. I couldn't get the service guy to tell me exactly what they did (prob doesn't know exactly since the tech did it) and he said they followed Subaru's ...59 posts · Joined 2015. #1 · May 23, 2020. I'd greatly appreciate some help troubleshooting a P0420 code on my '07 OB. I've reviewed many posts on this, including the P0420 Diagnosis post on the Problems and Maintenance forum, but I'm not understanding some of the basics. Many of the posts refer to checking for exhaust leaks.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 …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...Oct 22, 2023 · 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. Nov 30, 2018 · 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. 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.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 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 Code: Causes, Meaning, Symptoms (and How to Fix it) (mechanicalboost.com) 2021 Crosstrek Limited Crystal White / Black leather. (MNRF - 33) Moonroof Package W/Nav/HK AUDIO. Auto-dim Mirror/Homelink/Compassr + Side moldings All Weather Mats. Outside mirror Auto Dim Rear Bumper Cover LED lightsDoor Edge Guards.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 ...Conclusion. The P0420 code is an indicator of a problem with the catalytic converter in your Subaru. Common causes can include failed or malfunctioning components, such as the oxygen sensor, fuel system, EGR system, and exhaust system. It's best to take your vehicle to a professional mechanic for diagnosis and repairs.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.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 ...If you're considering an upgrade of your computer's operating system, Windows 7 Home Premium ranks among your options. The system requirements to install it depend on whether you'l...P0420 data interpretation, 2007 2.5 non-turbo. Hi all! Ive collecred some data and am hoping someone can help me figure out my next step. I have a 2007 outback. 2.5i. 200,000km. A few weeks ago, the coil burnt out and I lost cylinder 3&4. I drove about 5km home hoping to avoid a late night tow bill.P0420 is catalyst below efficiency. P0303 is misfire on cylinder 3. The misfire could be contributing to the catalyst problem so it should be addressed first. Pull the # 3 plug and look for carbon or wet with gas. The old plug wires are also suspect. Clean the plug and re-install. Check the connections on both ends of the wire.According to Popular Mechanics Magazine, diagnosing the cause of a P0420 code on a Subaru Forester can be done by checking for potential issues with the catalytic converter, oxygen sensors, and exhaust system.The performance of the catalytic converter starts with air, fuel and fire. Your engine performance determines the function of the cat and is the number 1 reason the P0420 pops up. That's why the code states "Catalyst Efficiency Below Threshold" and not "Catalyst Failure". Yours is MAF metered air, so I'm going to give you an example of how you ...VSurfn. 1329 posts · Joined 2014. #2 · Jul 22, 2018 (Edited) P0420 code stands for “Catalyst System Efficiency Below Threshold (Bank 1).”. When you receive a P0420 code it means your catalytic converter is not operating at maximum efficiency. Usually this means your catalytic converter needs to be replaced and/or your O2 (oxygen) sensors.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 …The most common fix for P0420 in the Subaru BRZ is a new catalytic converter, followed by an O2 sensor replacement. Before taking your BRZ 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 BRZ: 1. Check for Other Codes.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.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 …May 14, 2015 · This low kilometer Subaru Impreza flags a P0420 Catalyst efficiency fault code very quickly. The rear O2 sensor would behave almost like the catalytic conver... 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 ..."His was a life, full of gallantry, sacrifice, love for Nigeria and ever willing to die in order to keep it one." A good number of Nigerians have been through life under military r...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 …Hello everyone! Received this p0028 code on my 08 ll bean forester last weekend when going up to the mountain. Didn’t notice any issue running until I had to climb a pretty steep hill and rpms went over 4K. The car was physically shaking back and forth like it was going to stall until I took my foot off the gas a bit and brought rpms down.Even slight variations in the air/fuel mixture will cause the converter temperature to rise significantly. The “Catalytic Converter Efficiency” Diagnostic Trouble Codes (DTCs) P0420 and P0430, are among the top 10 DTCs technicians face. And while the description might imply a failed converter, odds are the ultimate fault lies somewhere …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 ...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...Jul 22, 2018 · VSurfn. 1329 posts · Joined 2014. #2 · Jul 22, 2018 (Edited) P0420 code stands for “Catalyst System Efficiency Below Threshold (Bank 1).”. When you receive a P0420 code it means your catalytic converter is not operating at maximum efficiency. Usually this means your catalytic converter needs to be replaced and/or your O2 (oxygen) sensors. 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...5784 posts · Joined 2018. #2 · Apr 12, 2023. There is a whole thread on this forum about the P0420 code, what can cause it and how to diagnose the cause. If you take the time to read the first 10 to 20 posts of that thread you may be able to diagnose the cause. The code can be caused by bad fuel, faulty O2 sensors, poor electrical …Dec 5, 2023 · 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. May 14, 2015 · This low kilometer Subaru Impreza flags a P0420 Catalyst efficiency fault code very quickly. The rear O2 sensor would behave almost like the catalytic conver... VSurfn. 1329 posts · Joined 2014. #2 · Jul 22, 2018 (Edited) P0420 code stands for “Catalyst System Efficiency Below Threshold (Bank 1).”. When you receive a P0420 code it means your catalytic converter is not operating at maximum efficiency. Usually this means your catalytic converter needs to be replaced and/or your O2 …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.B. bluewagon Discussion starter. 83 posts · Joined 2015. #1 · Mar 4, 2016. Hey guys, Like to get your thoughts on this. CEL went off with a P0420 code. FreeSSM description is "Catalyst System Efficiency Below Threshold:". From what I've gathered this kind of CEL could be fault of either the front o2, back o2 sensor or the catalytic converter.Dec 5, 2023 · 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. 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...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 ...4 days, 1 subaru wideband sensor, and 3 drive cycles later, I have clearing subaru readiness monitors down to a T. And the wide-band that came with my AEM failsafe gauge is looks to be the same model as the subaru wideband, except the resistors are different. But, the P0420 code was still there.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.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, …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...Went to autozone, and got the P0420 code. I've ordered a new front O2 sensor from subarupartsforyou.com and will try a few other suggestions. But why would the CRUISE light be flashing and the cruise control system be inop as well? I've seen a previous thread where someone had that, but just the P0420 code was addressed.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.P0420 data interpretation, 2007 2.5 non-turbo. Hi all! Ive collecred some data and am hoping someone can help me figure out my next step. I have a 2007 outback. 2.5i. 200,000km. A few weeks ago, the coil burnt out and I lost cylinder 3&4. I drove about 5km home hoping to avoid a late night tow bill.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...Jan 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 ... 5784 posts · Joined 2018. #2 · Apr 12, 2023. There is a whole thread on this forum about the P0420 code, what can cause it and how to diagnose the cause. If you take the time to read the first 10 to 20 posts of that thread you may be able to diagnose the cause. The code can be caused by bad fuel, faulty O2 sensors, poor electrical …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. ... /r/WRX is a place for Subaru fanatics to show off their rides, discuss modifications, mechanical issues ...Sep 6, 2017 · Like. Jay11STI. 3579 posts · Joined 2011. #8 · Sep 9, 2017. P0420 is generally a universal code for Catalytic Converter limit below threshold or something along those lines. P0420 indicates a failing catalytic converter. Correct me if im wrong but all Cobb downpipes are catted and have that high flow cat in them. Visit me at: http://www.ericthecarguy.com/O2 Sensor Video: https://www.youtube.com/watch?v=NIzcztO-CCsDiscussion about this video: http://www.ericthecarguy...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...Only way to keep the light off is to replace it. As u/oldslim pointed out, the second (downstream) O2 sensor is used by the ECU to determine if the catalytic converter is working at full efficiency. If the ECU judges the efficiency to have fallen below an acceptable threshold, the P0420 code is the result.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?Subaru Mechanic: Mike Alberghini. Hello! P0420 is referring t the exhaust system. it could be something like an exhaust leak, bad oxygen sensor, or bad catalytic converter. The other 2 codes are not real codes, and are due to your scan tool not knowing how to read the codes given to it by the computer.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 ...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.2001 OB H6 infamous p0420 help deciphering it. I have an ultragauge and for about the last year would get a random pending check engine code p0420, this is only like 4 or 5 times in an 18 month period. For those unfamiliar with the ultragauge a pending code is a pre code not enough to throw an official check engine but its getting close.PO420 code. Thanks for taking the time to help. I have a 2004 Outback 2.5L automatic. J259. Code P0420. I've replaced the bank 1 sensor 1 with a Denzo brand. I've ran 2 different cleaners through the gas tank. I got the car with a blown head but had it fixed. I replaced the sensor after the head was fixed.Summary. P0420 stands for “Catalyst System Efficiency Below Threshold (Bank 1).”. This trouble code is triggered when the on-board computer detects that the bank 1 of the catalytic converter is underperforming. A faulty catalytic converter (usually due to overheating and contamination) is the most common reason why this code is logged.This low kilometer Subaru Impreza flags a P0420 Catalyst efficiency fault code very quickly. The rear O2 sensor would behave almost like the catalytic converter had been removed. Replacement ...Any brand of motor oil is suitable for a Subaru as long as the viscosity is correct. Some Subaru models require synthetic oil. The type of oil also may depend on the year of the ca...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. 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...May 14, 2015 · This low kilometer Subaru Impreza flags a P0420 Catalyst efficiency fault code very quickly. The rear O2 sensor would behave almost like the catalytic conver... 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... 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... Nov 21, 2023 · P0420 Code Chasing - Graph of O2 Sensor. 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. I reset the code, and after about 60 miles I saw the code "pending" again though it wasn't confirmed and no ... 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 ...

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?. Gang colors

subaru p0420

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.Mar 13, 2023 · 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 ... Facebook page “likes” are an excellent way to gauge a company’s or brand’s engagement with potential customers. To better understand how to market your Facebook page, you should tr...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 …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. Desferal (Injectable) received an overall rating of 7 out of 10 stars from 1 reviews. See what others have said about Desferal (Injectable), including the effectiveness, ease of us...4 posts · Joined 2015. #1 · Nov 16, 2015. my 2004 Subaru outback with 140k miles and Cali emissions has been throwing the dreaded P0420 code for almost 2 years now. I snuck it past inspection with a well timed code reset. However I want my cruise control back. I've read a number of the write ups on the P0420 code.If you find a P0420 code in your Subaru or Honda, it’s most likely the catalytic converter to blame. It can also be caused by an exhaust leak or a bad oxygen sensor . Check for vacuum leaks or other fuel mixture-related engine codes.The most common fix for P0420 in the Subaru Legacy is a new catalytic converter, followed by an O2 sensor replacement. Before taking your Legacy 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 Legacy: 1. Check for Other Codes.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.The codes are: P0420: Catalyst System Efficiency Below Threshold (bank 1) P0422: EVAP Control System Leak Detected (Small Leak) I am now in a new area and went to a mechanic who wasn't familiar with my vehicle history. I explained my situation and mentioned to Rear O2 sensor issue of the past. This mechanic read the codes and said …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 exhaust flow ...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 ....

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