Code P0420

lchhung

Hi All,
Last year, my Yaris 2008 1L, was burning oil with 1.5L oil/1000 km, and I also got code P0420 at this time, and smoke came out like... in a chimney. I changed piston rings, gaskets... and oil burning was solved, no more blue smoke. So, hoped no more P0420.

However, anytime when I drive on highway with speed about 90-110 kh/h for about 100 miles or more, the engine light comes on with code P0420. The code never appears when I drive in city or high speed at short time.

Because of that, last October, I volunteered to do a NCT test to see how my car emission is, and passed all without any issue.

But, why this P0420 is still there anytime when I drive on highway at high speed in a long time? Do you think the problem is with the Cat or O2 sensor ? I cleaned post-O2 sensor but nothing improved. I have not cleaned pre-O2 sensor as it is too tight to take out now. I also clean the CAT by putting in in water with soak over night and watering it but no improvement.

Air filler, spark plugs are new, MAP sensor was cleaned.

Any suggestion?

rex-x

you need a new cat

nd

It's common on the older toyotas at least and doesn't effect passing emmisions.

So you can just ignore it or if the engine light is annoying you you can smooth out the post cat o2 sensor signal so the ecu doesn't trigger the engine light and code with a resistor and capacitor. I've done it on 2 toyotas and it worked.

https://www.youtube.com/watch?v=qHD7T7EhuzI

Toyotafanboi

Id agree with that.

Mams older 1.0 Yaris had P0420 and check engine light on for literally maybe 3-4 years. Passed NCT emissions every time, no problem.

Same with my Celica, I had P0420 for around a year and passed NCT emissions also.

I wouldn't usually say to ignore a fault but you can probably ignore that one.

lchhung

Perfect suggestion. Many thanks! I will try this weekend by putting a resistor and capacitor. Did you try NCT with this modification ? I was wondering it could fail NCT if NCT tester recognised these stuffs connected to O2 sensor ^_^. My NCT due is Oct/2019.

I dont want a new Cat as I got a quote with Toyota dealership, 500EUR for OEM.

nd wrote: »

It's common on the older toyotas at least and doesn't effect passing emmisions.

So you can just ignore it or if the engine light is annoying you you can smooth out the post cat o2 sensor signal so the ecu doesn't trigger the engine light and code with a resistor and capacitor. I've done it on 2 toyotas and it worked.

https://www.youtube.com/watch?v=qHD7T7EhuzI

nd

Yep. No that's no problem for the nct.

lchhung

nd wrote: »

Yep. No that's no problem for the nct.

Many thanks for great suggestion.

Have a great Christmas,

ofcork

I had that code on an avensis for a few years like others no problem with nct either main dealer wanted 800 for a cat.

toyotafan

ofcork wrote: »

I had that code on an avensis for a few years like others no problem with nct either main dealer wanted 800 for a cat.

What did you do finally? €800 seemed tobe crazy. I also fixed code P0420 with a 1Mohm resistor + 1microF capacitor for my Corrola 2004. Works perfect.

ofcork

Stupid money alright kept the car for over 7 years before trading it in late 2014 for a 12 avensis.

lchhung

@. Tested both front (old one) and rear (new one) sensors. I got results as shown in the attached image. Road test was performed on highway, no more code. Hope this will solve my P0420 code problem.

Test results showed when engine was fully warm up.

1. Front sensor voltage changed from 0.1 to 0.7 Volt at 3000 RPM.

2. New rear sensor voltage changed in between 0.55 -0.75 V.

I think both are OK now.

O2 sensor test reference by NTK: https://ngkntk.co.uk/wp-content/uploads/2011/04/5883-Lambda-Sensor-Pocket-Guide.pdf

DOX-0150 sensor: https://www.amazon.de/gp/product/B00CVZ1NEO/ref=ox_sc_sfl_title_3?ie=UTF8&psc=1&smid=A3JWKAKR8XB7XF