Hi. I have been getting a P0420 code about catalytic converter for a while on my fabia 2003 1.2 HTP 64hp AZQ.

Now it was time to inspect my car and it passed the emissions, only clearing the light.

So it seems that cat is working just fine, but the yellow light is quite annoying and  I want to get it away. There is somekind of spacers to oxygen sensors that should help. Like this: https://tinyurl.com/y858d4up

So, does post cat oxygen sensor affect to fuel mixture etc. on my car?

Sorry about grammar fails, not used to using english.

The post car sensor is only a monitoring sensor to check that the emissions are within spec.  The pre car sensor is a controlling sensor.

But if the engine ECU decides (from the relative values of pre- and post-cat oxygen readings) that the catalyst isn't doing well enough, it will adjust the mixture to attempt to bring the calculated emissions back to where it wants them to be.

 

Which country are you in, and which gases are tested in your emissions test? What were the figures/numbers it produced for each measured type?

Edited 29 April, 20206 yr by Wino

Just replace the rear sensor, they're cheap.

2 hours ago, Wino said:

But if the engine ECU decides (from the relative values of pre- and post-cat oxygen readings) that the catalyst isn't doing well enough, it will adjust the mixture to attempt to bring the calculated emissions back to where it wants them to be.

 

Which country are you in, and which gases are tested in your emissions test? What were the figures/numbers it produced for each measured type?

I'm from Finland and on the paper it says:

CO% 0,05: (limit. 0,2)

HC ppm: 20 (limit. 100)

Lambda: 1,01 (should be between 0,97-1,03)

These numbers are measured at 2500 rpm and for me these look good. 

37 minutes ago, sepulchrave said:

Just replace the rear sensor, they're cheap.

It might be it. But not sure because I've tried to put few litre RE85 to full tank and the light will turn off after a while. Also the reading on the OBD scanner also looks good. 

Yes, no problem or marginality about the measured emissions.

Part number of the rear sensor seems to be 03C 906 262 according to this page: https://skoda.7zap.com/en/cz/fabia/fab/2003-225/9/906-906000/#12  5th line of item 12s

 

I'm not convinced that'll help unless there's some indication that it isn't working correctly, with a specific fault code pointing to it, but maybe it's the cheapest thing to try.

 

Does the car do mostly short/urban journeys? If so, maybe it just needs more vigorous 'exercise' to burn the soot out of the system a bit?  

3 minutes ago, Wino said:

Yes, no problem or marginality about the measured emissions.

Part number of the rear sensor seems to be 03C 906 262 according to this page: https://skoda.7zap.com/en/cz/fabia/fab/2003-225/9/906-906000/#12  5th line of item 12s

 

I'm not convinced that'll help unless there's some indication that it isn't working correctly, with a specific fault code pointing to it, but maybe it's the cheapest thing to try.

 

Does the car do mostly short/urban journeys? If so, maybe it just needs more vigorous 'exercise' to burn the soot out of the system a bit?  

It's like 50/50 urban and motorway driving. But maybe I try to burn some carbon away and buy a new sensor.

The only sensor which will throw that cat code is rear lambda, since the emissions look good on the inspection sheet the cat is obviously lighting up and doing its job so the probe is probably duff, since it's not a wideband device the output will look plausible until it breaks.

Worth trying, yep.

How many km has the car covered?

 

 

Just now, Wino said:

Worth trying, yep.

How many km has the car covered?

 

 

Now about 216000 km

Probably a fair lifespan for that sensor.