I was throwing a P0420 code every tank that went into the vehicle once it got around a half tank no matter duration of the drive. I would clear the code and go on with life until the next time until the last 2 weeks it didn't throw the code until yesterday. I have also noticed since the first time it threw the code that I have an exhaust type smell in the cabin only when stopped. I've thought it was just an exhaust leak and some of the fumes were getting into the cabin along with being cause for the code up until the last 2 weeks where the smell got less intense and the code didn't come back. What could the problem be and are the 2 problems really related? I plan on checking the exhaust for leaks tomorrow night using a few methods found on here.
P0420 and exhaust smell in cabin when stopped sometimes
- Thread starter Qmb9015
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Nervo19
Member
I had that problem with my 2000 which now has a bit over 200k. PO420 is an oxygen sensor I believe. I bought the sensor but never got around to changing it. I would just reset the light and ignore it. The rear cargo area started getting a bit of exhaust smell and ultimately on a long trip it got so hot a plastic bag melted onto the Weathertech liner. It turned out a hole developed on top of the exhaust pipe. So new downstream oxygen sensor, muffler and Walker exhaust and it's fixed. The gas mileage improved a bit too. Amazon has great prices on Walker exhaust and mufflers and Denso oxygen sensors.
Thanks bud i will check better on the exhaust better because the smell is in the front of the cab so i need to get it fixed soon.
TheDurk
Elite Member
O2 sensors are only one of the possible causes of a P0420. Exhaust leaks are a cause but only upstream of the rear O2 sensor. A hole in a muffler is NOT a possible cause. I just wanted others with that code to be clear about what is needed to fix their problem. Muffler and tailpipe won't help.
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The code is for Bank 1 below threshold. I am not sure if that is the upstream or the downstream but lets say it is upstream and i have a leak. If i get that leak repaired or section replaced then the code SHOULD go away?
Nervo19
Member
If you read what I wrote I had a hole in the exhaust pipe. Muffler was cheap to replace at the same time. Anyway with new oxygen sensor and pipes there's been no CEL for over 1500 miles.
Nervo19
Member
Check the gaskets (donuts) going into and out from the catalytic converter. My other truck leaked there. The gaskets are about $6 each at any parts store. You probably still need an oxygen sensor.
Ill check them when i go back under to look for holes again. Im waiting on O2 sensors until i get my live read OBD2 in that monitors the sensors output to see if it just dies randomly or if they are reading correct and that i am just getting an increase in air or fuel in my exhaust.
TheDurk
Elite Member
I read it. The rear cargo area is too far downstream to cause a P0420. Any leak needs to be upstream of the rear sensor. It was the new O2 sensor that cleared your code.
TheDurk
Elite Member
The P0420 is not specific as to cause or location. It's just that anything below the rear sensor won't affect the sensor readings. Bank 1 is meaningless in a vehicle with a single exhaust; that's all there is until you get to the engine itself, which obviously has two banks (if a V6). The problem can be either exhaust sensor, although usually the rear one, exhaust leaks above the rear sensor, or compromised cat converters.
IF the leak is the cause, the code will eventually clear, but it may take a while, like a tank or two of gas. It will clear more quickly if you use a reader/scanner or just pull the EFI fuse for 30 seconds or so, or pull the negative cable on the battery for the same amount of time.
P0420 test protocol requires two trips to detect or reset, and a very specific set of drive pattern events has to occur. I'd suggest clearing the code (which restarts the test process) to speed things up.
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TheDurk
Elite Member
Why? The leak is more than capable of causing the P0420 on its own. And he obviously has a leak IN THE FRONT, where it matters as far as a P0420 goes.
So after talking with a coworker i have a question. What if one of my convertors (i have 2 and just found out i have a cali version) gets clogged intermittently that causes the code and causes a leak where the the mid sections bolt onto the rest of the exhaust?I just got my code reader today and it shows my O2 sensor runs between .3 - .675V depending on idle or driving. Does that sound about right?
SO now that i have a live data code reader i have been watching my O2 sensor and it stays mainly between .3 and .7 with occasional drops to .25 and spikes to .8. There was though about a 15sec period yester day though while doing 50mph that it dropped to .015 and stayed around there. I would assume that means the sensor is going bad correct? It doesnt explain the occaional exhaust smell but it would explain the code.
TheDurk
Elite Member
Front or rear sensor? Cali. or Federal?
The P0420 sets when the comparison of front and rear sensors indicates that the cat converters aren't reducing the contaminants in the air. It needs to see a flatter line with more time between switches out of the rear than out of the front. You really can't look at one in isolation from the other for a P0420. The sensors degrade when they don't switch as quickly between a higher voltage and a lower voltage as they should. My rear sensor now is up to 80k again, so I'll probably have to do it soon. It went at 90k the first time. No specific code, just the P0420.
The ECU in responding to A/F sensors in Cali rigs actually does not react to voltage, it react to currents and it is more difficult to interpret and compare the sensor readings. To be honest, I have never figured out how to do it.
A truly defective sensor will throw different codes.
My approach to a P0420 on my rig has been that 1) I fix any exhaust leaks. 2) If the rear sensor has more than 75k on it, I change that. So far two small exhaust leaks and one rear sensor has kept me on factory cats despite three P0420s. Our trucks are at an age where those exhaust gaskets are all turning to dust (except mine, which are all new this summer, as well as muffler and tailpipe.)
If I were you, I'd fix my exhaust leak first, and then see where I stood. Unless your sensors are north of 80 or 90k, then you might as well change them as good PM.
If your cats are physically damaged, leaking, rattling inside, or smelling of sulfur at the exhaust, then they need to be changed and anything else is wasting time--although you want new sensors with new cat(s), so changing those first makes sense.
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Its a 2001 sr5 4wd Cali with 234k miles. Ive had it for 2 months so i will have to check the 3 inch stack of papers again to see if or when the O2 sensor was last replaced. My scanner shows the value for the downstream sensor and i dont think it shows the A/F sensor unless its abbreviated weird. Ever Since I created this post i havent smelled the exhaust smell in the cabin except real faint once but i also havent been driving it for longer that 20 mins at a time this week. I have smelled my exhaust at the tip and it really doesnt have a smell and there is no noise coming from the converters. The only noise i hear is after i shut it off i can hear a metallic tapping noise coming from inside my muffler like someone is dropping ball bearings in it.
Hi - I’ve got a similar issue at the moment and was hoping someone could shed some light. 99 4runner cali spec threw a P0420 after some harsh weather. Thought it was the O2 sensors, replaced those and still got the code.
Plugged in my shopvac today and found an exhaust leak between the two cats. Picture for reference
05-AE2-A31-C55-A-4-BF2-A9-E3-C5-F9-E322-EBBB hosted at ImgBB — ImgBB
Is there a gasket between the two connectors of the cats? The nuts are rusted shut and so will likely need to cut it off. Other option is to completely weld/seal together the two gaskets…
Also wondering if this is the reason for my p0420, don’t want to go down a rabbit hole for no reason.
Plugged in my shopvac today and found an exhaust leak between the two cats. Picture for reference
05-AE2-A31-C55-A-4-BF2-A9-E3-C5-F9-E322-EBBB hosted at ImgBB — ImgBB
Is there a gasket between the two connectors of the cats? The nuts are rusted shut and so will likely need to cut it off. Other option is to completely weld/seal together the two gaskets…
Also wondering if this is the reason for my p0420, don’t want to go down a rabbit hole for no reason.
