P0420 error (Catalyst System Efficiency Below Threshold )

[ThinkPad]

So,

Since a while we are seeing the check engine light pop up sometimes on our Yaris 2006 (1.3 engine 2SZ-FE) with manual transmission.

When connecting the OBD-reader, it sees a P0420 error, which stands for "Catalyst System Efficiency Below Threshold Bank 1".

I saw this for the first time about three months ago. Had some issues with the rear muffler, but that one was replaced for a original one by the dealer. New muffler sits under the car for about a month now, but i saw the P0420 again last week. I have resetted it and it will stay of for a few weeks/month.

However, what is the cause of this and how can i solve it more permanently?
I am afraid of replacing the catalytic converter, as that part is $$$$ expensive and i read that sometimes it won't even solve the problem as Toyota's are quite trigger happy for this P0420 error?

Is there someone who has dealt with this error before? Car runs fine otherwise, no issues. Mileage (see signature icon) is also fine.

[06YarisRS]

So,

Since a while we are seeing the check engine light pop up sometimes on our Yaris 2006 (1.3 engine 2SZ-FE) with manual transmission.

When connecting the OBD-reader, it sees a P0420 error, which stands for "Catalyst System Efficiency Below Threshold Bank 1".

I saw this for the first time about three months ago. Had some issues with the rear muffler, but that one was replaced for a original one by the dealer. New muffler sits under the car for about a month now, but i saw the P0420 again last week. I have resetted it and it will stay of for a few weeks/month.

However, what is the cause of this and how can i solve it more permanently?
I am afraid of replacing the catalytic converter, as that part is $$$$ expensive and i read that sometimes it won't even solve the problem as Toyota's are quite trigger happy for this P0420 error?

Is there someone who has dealt with this error before? Car runs fine otherwise, no issues. Mileage (see signature icon) is also fine.

I will be watching this thread. I replaced the downstream 02 sensor as I had a P0137 code (Oxygen sensor circuit low voltage B1S2). I also had zero voltage from the sensor. After the sensor was replaced that code disappeared and I had appropriate voltages from the sensor 0.1 - 0.9 volts. Fast forward a few hours and now I have the P0420 code, just like you. I do know that I have a small exhaust leak but it is well after the post-cat sensor. I am waiting to hear what others have to say. I'm also wondering why I didn't see the P0420 code earlier and wondering if it has to do with the inexpensive sensor I put in. My air fuel ratios are great, so I don't think it's doing any harm, but I hate MILs.

EDIT: The downstream 02 sensor should have a steady voltage unlike the upstream sensor which fluctuates between 0.1 and 0.9. My downstream sensor was fluctuating. I may have a bad cat. I will try the antifouler and post back.

[ex-x-fire]

The senior tech at work said he never got rid of the code P0420 (on any car) by replacing the o2 sensors. If the tune up is good & the fuel pressure is in spec, I'd be looking at a cat.
How many miles are on the car?

[tmontague]

proper fix is likely a cat replacement. Cheap fix is using an O2 defouler in the O2 bung

[kiimboy]

I'm just curious how many o2 sensors does a yaris have? I have a 2009 toyota yaris, 4 cyl, sedan. I also have the annoying p0420 -_-

[tmontague]

2 in total, and wideband pre cat and a typical O2 sensor post cat.

Its the post cat one that is triggering the code

[kiimboy]

Is the post cat one the downstream? Sorry, a car noob here lol

[06YarisRS]

Is the post cat one the downstream? Sorry, a car noob here lol

Yes, the post cat is the downstream 02 sensor. I am going the plug defouler route since my air fuel ratios are solid. I picked a kit up this evening.

[kiimboy]

How do i check my air fuel ratio?

[06YarisRS]

How do i check my air fuel ratio?

I'm using my OBD 2 bluetooth adapter, Torque Pro app on my android phone. Among many other sensors monitored are both commanded AFR and measured AFR. I am in Niagara Falls now but when I return home in a couple of days, I could send you a pic if interested.

[kiimboy]

I also have an obd2 scanner, how can I tell if the air fuel ratio is good? Yes please send me the pic, thanks!

[esse10]

Don't go off buying a new cat or O2 sensors just yet sometimes all it needs is a little cleaning of the carbon buildup. Here is something you can try and I am almost 90% sure will fix that P0420 code from coming back. Get a can of
SEAFOAM at your local parts store and spray a little at a time to the car's intake while it's Idling. DO NOT, put too much or you'll lock your engine up.
spray about 4 Oz with a spray bottle or let the vacuum suck it into the intake with a clear poly tubing just use a tapered edge end. Good luck.

[komichal]

Get yourself a can of OXICAT and pour it into the gas tank.
I think that one can actually suffice to two tanks.
Thats the first aid for cat/O2 issues.
So far I was lucky and had no P0420 on my 2007 Yaris but a friend of mine had it on his Skoda car and OXICAT helped him.

[06YarisRS]

I also have an obd2 scanner, how can I tell if the air fuel ratio is good? Yes please send me the pic, thanks!

Here is a pic from my phone. Of course since the car is in New Brunswick and I am in Toronto, the connection would probably be a bit shaky. :laugh:

I will post a pic tomorrow while connected and engine running.

The commanded (c) and measured (m) under normal conditions both hover around 14.7:1. Let off on the gas and it's around 18:1 (lean), push the pedal and briefly you'll see the fuel component increase a bit (rich).

https://i.imgur.com/QdUU21G.jpg

[06YarisRS]

Here is the AFRs with engine running. I think I was crusiing on the highway at about 120 km/h.

I gotta say, I'm super impressed with this little engine and trans combo. This car barely slows down a hill. At around 2900 - 3000 RPM, where it seems very comfortable, it just sings up long hills without any additional input on the accelerator. This was with my wife, two kids in the car and probably 60 - 80 pounds of packages in the hatch. It flies right along without any big production or complaining on behalf of the powertrain.

https://i.imgur.com/4yYtbcn.jpg

[06YarisRS]

Going on two days and no more MIL. At first, I installed one sparkplug defouler and still got the P0420. I screwed on another taking the sensor ever farther back from the stream. So far so good. Monitoring my downstream sensor, I now see steady voltages. Fingers will remain crossed for a bit.

[tmontague]

2 should do it

[06YarisRS]

2 should do it

You're probably right.

[ThinkPad]

Bit of a late reply. I ordered a set of 'defoulers' (link (https://www.aliexpress.com/item/Car-Exhaust-O2-Oxygen-Sensor-Test-Pipe-Extension-Extender-Adapter-Spacer-M18-X-1-5-Bung/32851931768.html)).

I can't get the O2 sensor off, it seems very stuck. Strange thing is that the sensor before the cat was easy to get loose (just for trying, nothing else as the defouler needs to be placed on the second sensor). So i'm sure the direction (lefty loose) is correct. I unclipped the connector, put the wire through the ring spanner, put the ring spanner on the nut. Tried hammering on the end of the spanner, but no movement :(

Also i'm not sure if i have enough free space between the sensor and other parts (transmission, manual in my case) for the defouler(s) to fit. Seems quite tight space.

Does anyone have pictures of the defouler(s) fitted on his/her Yaris?

[ThinkPad]

We still have a P0420 error message on our Yaris 2006 sometimes. It only appears when you drive at a constant speed of around 80-100kph it seems.

Have tried before to place a 'defouler' but i couldn't get the second lambda sensor loosened. But it also won't fit i guess, as the sensor is mounted at a weird angle which doesn't give much room for the defouler.

Have recently let Torque log via OBD during a 20 minute highway ride. I filtered the output in Excel at engine rpm> = 3000 so that I only have the highway piece.

Both sensors (upstream & downstream) in one graph:
https://tweakers.net/ext/f/YUvUsiRCDqlhohrXLTORuZGy/thumb.jpg (https://tweakers.net/ext/f/YUvUsiRCDqlhohrXLTORuZGy/full.jpg)
(Click for big picture)

Both sensors separately:
https://tweakers.net/ext/f/298L4drT8p7dcPJoK5U5AKua/thumb.jpg (https://tweakers.net/ext/f/298L4drT8p7dcPJoK5U5AKua/full.jpg)
(Click for big picture)

When I look at the combined graph, I think: hmmm the 2nd sensors fluctuates a lot. But if I look at the graph of downstream separately, then I think: it is not too bad, value is fairly constant.

Is there someone who can say something about the condition of the catalytic converter?

[ThinkPad]

Nobody?

[ThinkPad]

After driving for some years with this error and clearing the Check Engine Light (CEL) regularly, I ended up replacing the secondary O2-sensor (the one behind the catalytic converter).
I used a Denso DOX-0109 sensor for which i paid around €48/$55. This version you re-use the connector from the old sensor. A ready to install sensor was about double the price of this Denso.

Placing the new sensor was easy, but removing the old one was a real pain. It was very, very stuck because of rust (due to salt used on the roads in winter here). I removed the exhaust from under the car, otherwise i could not put enough force on the sensor to remove it, even when using lots of penetrating oil. In the removal process the thread got stripped, but luckily a friend of mine had a thread cutter for M18x1,5. After that was done, the placement of the new sensor was easy. Copper grease was supplied with the new sensor to prevent it getting stuck again.

I have driven around 700km/434mi since, and the CEL hasn't turned on anymore, whereas normally it would light up within 50km/30mi after clearing the CEL.

When looking at Torque, i can see that the sensors now show normal behaviour. The first sensor shows a waveform, the second one shows roughly a flat horizontal line around 0.5 - 0.6V when drving at a constant speed. Before, the second sensor was mimicking the first one. I would really have thought the catalytic converter was shot, but so far it just seemed to be a faulty sensor. The car mileage is 154k km/95k miles.

By the way, i ended up not using the 'spark plug defouler', as the angle of the sensor is quite bad, with the defouler in between the sensor would not fit between the exhaust pipe and gearbox.

[komichal]

Same error here - P0420, always came back after a few days after cleaning.
I also decided to change the post-cat O2 sensor before doing anything with the cat. I used the Denso direct fit - costs more but saves time with soldering etc.

As ThinkPad mentions - removing the sensor is not that easy but at the same time it went better than I expected considering all the salty roads here during winter. I just poured some WD40 on it the day before. On the day D when I arrived home I jacked the front part of the car up a bit, sprayed it again with WD40, I used the O2 sensor hexa-socket, put it on the ratchet, put 1m pipe on the ratchet and PULLED. It was tough even on the 1m pipe but it suddenly CLICKED and I was able to unscrew it with ratchet only.

I also changed the upper O2 sensor, again with the particular Denso direct fit type. If the bottom O2 sensor was tired then the upper one must have been on its way too. The upper one was easy to unscrew - no need to use the pipe, just the ratchet with the socket and it went nicely.

This was half a year ago. No P0420 since then.
Fair to say - I have not noticed anything with the new pre-cat O2 sensor - no better engine run, no consumption improved. But actually I do not care that much. That P0420 is gone.

[komichal]

Tadah! A year and a bit passed away and my P0420 is back.
Will try OXICAT first to see if it helps. I do not think it makes sense to replace the downstream O2 sensor again... may end up with a new cat... or maybe just the defoulers...