How To Address a Subaru P0420 (Step by Step)

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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 NOBODY has ever done it, or made it a priority or anything.
Headgaskets, timing belts and water pumps are seemingly more important. Heaven forbid your piston meets a valve after an original timing belt shreds itself at 240,000km.
By all means, share experiences in the comments, or tell me I'm an idiot. If you do, at least I'll know you've read this far.
My personal car for some time was featured in this video, it was a 2008 Impreza hatchback base model - drum brakes and all. Mine had 2005-2009 LGT alloy front control arms, poly bushes in front, rear subframe poly bushing inserts, leather steering wheel, OE roof racks, tweeters and an OE WRX cat-back.
Man, I miss that car. So much fun for how it wasn't designed to be much fun at all. Way more fun sideways at 30km/h than I've had in a GTi at 250km/h.
Subaru EJ253 Coil Test
www.subarupartsplus.com/blog/....
Subaru Idle Relearn
www.subaruforester.org/thread...
Subaru O2 Sensor Ohm values
PlainOM:www.subaruoutback.org/threads...
How to Check Subaru O2 sensors
www.subaruforester.org/thread...

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29 июн 2024

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Комментарии : 62

@legneil 11 месяцев назад

No rattle on PCV valve your wrong on that one you should hear the clicking freely.

@NSUGS 11 месяцев назад

Thank you, I will pin your comment.

@legneil 11 месяцев назад

@@NSUGS np

@NonTypicalRacing 10 месяцев назад

I didn't read comments before I typed it, just watched vid. Maybe edit...?

@ede4345 5 месяцев назад

I just bought a new one and yes I hear something when I shake it.

@rock962000 Месяц назад

Yeah, no rattle means your PCV valve is stuck lol

@thedillestpickle 8 часов назад

I had a P0420 about 2 months ago. Pulled the whole exhaust system off. Replaced both 02 sensors. Dunked the whole Cat into an ultrasonic parts cleaner for an hour at 70C . Put it all back together and it seemed to work. Today I had a misfire on cylinder 1 and 3, but I think that's an ignition issue.

@NovaScotiaCarScene Год назад

Another Great video!

@udumkopf8217 8 месяцев назад

Thanks for the comprehensive breakdown...

@NSUGS 8 месяцев назад

No worries!

@mattcasabene6442 Год назад

Great video- just what I was after. Cheers

@NSUGS Год назад

Thank you! I made this video to capture my experience with a P0420, given these cars are at a minimum 100,000km, other systems and components must be considered. If nothing else, due diligence and preventative maintenance: an art in it of itself.

@NonTypicalRacing 10 месяцев назад

A PCV (positive crankcase ventilation) "does" rattle if it is good. When they are gummed up, they won't rattle.

@NSUGS 10 месяцев назад

See pinned comment

@Mojo522 10 месяцев назад

Thank you so much for this checklist; I genuinely appreciate it. I'm facing this problem in my 2011 Subaru Impreza Outback Sport 2.5i.

@NSUGS 10 месяцев назад

The amount of research I did and talking with heaps of people, no way I could keep that info for myself, given how common P0420 is with aging Subarus. Very glad to hear my work is bearing fruit for others! OE brand items are definitely key to solving P0420 for any amount of time. All things being equal and no other worn/sub-par items like leaky valve seals, a headgasket leak or carbon build up. NASIOC user 'Plain OM' (I think I got that right) is a wealth of knowledge.

@piority9 Год назад

Im the guy you sold the mower to. Nice videos man!

@NSUGS Год назад

Hey! Thank you! Currently on a roll of nonsense, but technical videos to come.

@Nhfilz 4 месяца назад

Thanks for your videos man, greatly appreciated. I’m $1600 USD deep in a 2009 Impreza (mechanic needs a new boat maybe ?) and they’ve yet to address the CEL/TCS/Cruise lights with codes P0420 and C0057. I’m going to have a go at your list. Cheers and thanks for documenting all of this.

@NSUGS 4 месяца назад

Keep in mind, boxers like to scuff pistons and burn oil, certainly an economy car with a boxer is no exception. Ask any Porsche boxer engine enthusiast, BMW boxer enthusiast and obviously a Subaru enthusiast. I mention this because while yes, replacing parts can help, if there's a preexisting issue with oil consumption, your car will eventually always have a P0420 due to a clogged cat or fouled sensor(s). I cleared my P0420 with new OE Denso O2 sensors and a cheap cat/header and the code went away for a few months at best. Take this video with a grain of salt, but by all means, give 'er a go, you have my blessing. But don't loose sight of the bigger picture!

@Nhfilz 4 месяца назад

@@NSUGS what would the preexisting oil consumption be caused by? Mechanic said it was timing belt or plugs, so they did that whole process and the light came back on immediately after I left the shop, next day they said it needed plug wires and an oil change, (don’t know why that wasn’t done with timing belt but.. light came right back on. I’m at my wits end and have dumped 2k into it this week. I’d be really pissed if the answer was to replace the engine or deal with not having traction control and cruise control.

@NSUGS 4 месяца назад

Oil consumption in a boxer typically comes from piston skirt wear, it's just inherent with the design, gravity isn't helping. If you're keen with tools, the list on the video is really not hard to do yourself. You could try O2 plug extensions, I have no experience so can't recommend anything. But if you're at your wits end, you have nothing to lose. Use quality parts otherwise. Sorry I don't have much else to offer. Any questions, feel free to reach out.

@NSUGS 4 месяца назад

Edit: timing belt replacement really won't have any noticeable effect on how the car burns fuel which is where a P0420 comes from. Start with cheap and easy parts, work your way more complex and more expensive parts unless it's obvious.

@williamngo8345 3 месяца назад

@@NSUGS which o2 sensor is this one for? The location? Bottom right side?

@brandenrohrer5066 Год назад

How about 02 risers ? I have one on my car still messing around with it. It works for clearing the check engine light but it does come back sometimes when I use cruise control 08 subaru impreza 2.5i

@NSUGS Год назад

I did not cover O2 sensor risers because I consider them a band-aid type fix, masking the problem. You're attempting to fool the computer. I suggest buying the best parts you can, OE if nothing else. Obviously not everyone can afford a $2000cad OE cat. But, the video hopefully, you got something out of it that helps. That's all this is: perspective and opinion.

@Lafue108 3 месяца назад

Hey you forgot the electrical tape trick. ie. electrical tape over the check engine light.

@LanceCastillo Год назад

Don't forget to check your warranty for a free catalytic converter replacement. Just got mine scheduled to be replaced for free today by Subaru due to the 15y/150k warranty for cats in pzev states like NJ. OEM ftw.

@NSUGS Год назад

Up here in Canaderp, we were not so fortunate. Though we did get the class action suit with the new-for-2013 2.0L engine oil consumption issue.

@stephaniecastro2721 Год назад

Where do you check if your car has the warranty

@NSUGS Год назад

@@stephaniecastro2721The dealer is a good source for that type of information.

@YoungShizzie Год назад

I have the same code on my 2004 Honda accord ex sedan replaced the whole exhaust and code came back crazy

@NSUGS Год назад

I used a cheap, aftermarket catalytic converter on my Impreza, the P0420 code came back after ~20,000km. IIRC, a higher content of palladium and Rhodium are key for a high quality exhaust. However, there was about $1000 difference between the product I purchased compared to an OE unit.

@YoungShizzie Год назад

@@NSUGS same I paid 160$ for mine and the comments said on there the code mite come back because it’s cheaper and made out of less medals but I’m not spending 900$ on a car for a fean to steal ya know but the only thing I didn’t change was the downstream sensor and when I put high octane from Wawa the little bottles the code goes away for like a week but mine stayed off for a month after I replaced the cat and whole exhaust

@NSUGS 4 месяца назад

Nice

@thedillestpickle 8 часов назад

@@NSUGS I got about 5 years on a $200 cat and I think I got about $150 exchange when I took my old cat to the scrapper.

@Crestone-saju Год назад

What about rear side Catalytic converter. What mileage you need to replace them before going bad?

@NSUGS Год назад

There are no O2 sensors supporting the functionality of the second catalytic converter. At least for 2.5i models. Pzev cars may be different. Basically, as long as it isn't clogged, it's assumed fine. Because there aren't any sensors telling the computer what's happening, the car doesnt know or care.

@Crestone-saju Год назад

@@NSUGS thanks for reply

@brandenrohrer5066 Год назад

Also is it know for cats to go on these subarus mine is an 08 with only 60k

@NSUGS Год назад

My experience with aircooled 'boxer' engines from BMW-land, lends itself to show boxers take a wee bit extra time to break in and burn a wee bit of oil given the inherit design architecture, this does not suprise me. Believe me, I lived both experiences.

@jeffryblackmon4846 2 месяца назад

Humor and good work combined. Using the parts cannon? Not recommended.

@NSUGS 2 месяца назад

Agreed, but with unknown history and clear neglect fom previous owners, it often doesn't hurt to ignite the parts canon. The key take away is to start trying with simple and cheap solutions, working to more complex and expensive solutions. Thank for for the feedback, I no longer own a subaru currently, but similar content will be a staple of this channel.

@danmc2678 Год назад

A new right front Cat is $2900 from Subaru! No aftermarket convertor matches my EFN# for California unfortunately. I have done all of these except premium fuel and the upstream cat. I even cleaned the cat, took it off and looked at it with a camera from both ends. It is spotless. The P0420 continues.

@NSUGS Год назад

I can only offer my condolences. My only other thot is being a boxer engine, gravity inherently acts like a bitch and scuffs up the bottom of the cylinder bores. Such causes wear, thus oil seepage...something I sincerely hope evades my RnineT.

@thedillestpickle 8 часов назад

@@NSUGS Mine has 290,000 km and burns oil like crazy. After I bought the car I checked the dipstick and there wasn't even any oil on the stick. So I think the owner was never even topping it up. Now I overfill it by about a quart often just so that I can get by a few weeks before I have to check it again and top off.

@stevepilant7894 11 месяцев назад

$22 each for ngk laser iridium

@NSUGS 11 месяцев назад

Gotta wait for them sales, guy

@DaDaDo661 5 месяцев назад

I got them for about $15 each on Rockauto

@NSUGS 2 месяца назад

Rock auto is such a fantastic resource, not just for buying parts but also cross references. That's how I figured out 05-09 Legacy share nearly the whole front suspension with 08-11 Impreza and 08-11 Impreza rear suspension is identical to first-gen BRZ