I saw this code in OBD2 scanner on Skoda Fabia 1.2 2006 64hk petrol.

It doesn't matter to me except that the car failed the inspection and I'm not allowed to drive it any more.

The problem was too high CO value. They said the other greenhouse gases and lambda value where OK!

Now in OBD I compared the lambda sensors pre & post cat, and the chart looks good I guess, this is a test drive, slight hills, warm engine, country side 80km/h, 2500rpm. enter image description here

Now I guess I can say the sensors are fine (they're recording) and the catalyst is doing its job.

HC and NOx values are within range.

CO was 0.0 last year, now it is 0.4, while the limit is 0.2

Lambda value is 0.99 where 1 is perfect and limits are 0.97-1.03. 0.99 means a bit rich fuel mixture.

Spark timing advance (TA) is around 26 (is that normal?)

Intake manifold pressure (MAP) average 55 (min-max 22-100)

Oil, oil filter, air filter are recently replaced. Spark plugs are replaced but I doubt that I installed ones with smaller gap.

The car specs says 0.9mm gap, and I installed 0.7mm. Can that be an issue?

I can't put my finger on whats wrong. I added K-sprit to the fuel, it is sort of injection engine cleaner and will take to inspection again this week.

What else can affect CO value? the fuel consumption is slightly higher than usual, but not a great deal.

No other error codes and no lamps are lit.

  • Can you supply the gas readings from the tailpipe test? And the pre and post O2 sensor chart from you car? If it looks like the one you referenced and the catalyst was full warmed up the catalyst has probably worn out. Nov 25 '16 at 23:47
  • @FredWilson The pre/post sensor chart are as reference, except on idle, they look good. The emission test says CO: 0.4 where 0.2 is max accepted. and lambda is 0.99 where 0.97-1.03 are the range, means the fuel mix is a bit fat but not so bad.
    – Aus
    Nov 27 '16 at 1:21
  • I didn't doubt the catalyst because HC level is normal, I guess this should be high too if the cat is broken, right? The oil looks dark even after I replaced it, I will change it again tomorrow just in case I did something wrong.
    – Aus
    Nov 27 '16 at 1:25
  • The HC can be low with high CO and still be a bad catalyst. It depends on what gasses the engine is feeding the catalyst and it what amounts and the average mixture. Catalysts use different processes to reduce fuels and NOx. It is actually quite an interesting set of processes. This is why I was asking for the numbers and O2 graphs. The oil quality will not matter to the catalyst. Nov 27 '16 at 2:35
  • @fredwilson Thank you for uor answer. It is good to know what affects what. It is a bit of magic (chemistry) in catalysts. And there goes a 500$.
    – Aus
    Nov 27 '16 at 15:14

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