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Old 09-27-2017, 04:21 AM   #1
ThinkPad
 
Drives: Yaris XP9 1.3 '06
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P0420 error (Catalyst System Efficiency Below Threshold )

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.
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Old 09-27-2017, 03:06 PM   #2
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Quote:
Originally Posted by ThinkPad View Post
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.
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Old 09-27-2017, 07:08 PM   #3
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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?
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Old 09-27-2017, 08:23 PM   #4
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proper fix is likely a cat replacement. Cheap fix is using an O2 defouler in the O2 bung
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Old 09-27-2017, 08:37 PM   #5
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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 -_-
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Old 09-27-2017, 09:03 PM   #6
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2 in total, and wideband pre cat and a typical O2 sensor post cat.

Its the post cat one that is triggering the code
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Old 09-27-2017, 09:22 PM   #7
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Is the post cat one the downstream? Sorry, a car noob here lol
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Old 09-27-2017, 09:52 PM   #8
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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.
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Old 09-27-2017, 10:36 PM   #9
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How do i check my air fuel ratio?
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Old 09-28-2017, 08:12 AM   #10
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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.
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Old 09-28-2017, 03:24 PM   #11
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I also have an obd2 scanner, how can I tell if the air fuel ratio is good? Yes please send me the pic, thanks!
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Old 09-28-2017, 03:42 PM   #12
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easy fix P0420

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.
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Old 09-28-2017, 03:59 PM   #13
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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.
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Old 09-28-2017, 09:23 PM   #14
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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.

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).

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Old 09-29-2017, 08:23 PM   #15
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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.

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Old 10-02-2017, 08:09 PM   #16
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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.
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Old 10-02-2017, 08:13 PM   #17
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2 should do it
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Old 10-02-2017, 10:04 PM   #18
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2 should do it
You're probably right.
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