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Niran gomes

P0420 Hyundai Sonata H-matic

Question

hi,

as you may have already seen in the description, i am having a p0420 engine code for a catalyst efficiency in bank 1 (4 cylinder engine). one problem ive noticed  is that sometimes after a rather short trip of say about 5-10km i do get a very strong smell from the exhaust, strong to the point my eyes tear( or at least i smell it.)  plus i always have to top off engine oil every 3-4 weeks or so with about 400ml - 500ml of oil. (using sae 40 caltex.) are these problems somehow related to the p0420?

i will check the spark plug ends tomorrow for oil.

the engine definitely is running as it should, and it runs very smooth except for very very rare occasions with small random misfires, new plugs would do i guess. i mean if the engine is burning oil, it should run rough and idle different right?

as per the code, how should i go about diagnosing it.

please do leave your ideas on this....

   

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9 answers to this question

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Half a litre of oil being burnt per month is not normal. What's the mileage of the car? 

My advise would be to fix the oil burning problem because in your case, I believe it is contributing to the P0420. From what you have described, it could be oil clogging up your catalytic converter (explains the exhaust smell) , or a gasket leak. 

Even after the engine is fixed, you might continue to get the error code depending on the condition of the catalytic converter and downstream Oxygen sensor. 

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A quick search says one cause can be oil contamination that causes the P0420 code to come up. But a more specific search says that in Sonatas, mostly oxygen sensor (O2) malfunction can cause this code to come up. Let's wait for the experts to have a proper say in this.

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On 1/4/2020 at 7:23 AM, Davy said:

Half a litre of oil being burnt per month is not normal. What's the mileage of the car? 

192,000km's

But it sure does not run so, it runs super smooth for that milage,(one reason i got it at 185000.) And again, about the oil burning problem, shouldn't the engine run really rough and shouldn't i see a bluish smoke out the exhaust? I see none of these signs except the smell... And i did happen to pull-out two sparkplugs out, cylinder 1 and 3 and the ends look normal. I don't see any signs of oil. Which kinda brings out the obvious question, am i leaking oi? 

No I'm not. I see a little bit of damp ness on the timing belt cover and that's pretty much it no puddles of oil underneath... Doesn't explain the 500ml per month. 

This is a rather unusual problem i guess, i feel like replacing the cat-con just for the sake of it, but the oil consumption?  And code..

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On 1/3/2020 at 9:45 PM, □AVANTE□ said:

mostly oxygen sensor (O2) malfunction can cause this code to come up. 

You mean faculty 02 sensor making the engine not run right (to rich)  and there by making the Cat-con go bad?

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Posted (edited)
4 hours ago, Niran gomes said:

You mean faculty 02 sensor making the engine not run right (to rich)  and there by making the Cat-con go bad?

Yes. If it did run too rich it could explain the nasty smell too. Did you note the fuel consumption? Also make sure to clean out any carbon deposits. Have you got it checked with a mechanic or expert?

Edited by □AVANTE□

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10 minutes ago, □AVANTE□ said:

Did you note the fuel consumption

yes, that i did a few days back.....then again i didn't mind it all the much....

 

12 minutes ago, □AVANTE□ said:

checked with a mechanic or expert?

no i haven't, thats the best way to go about it,  but i just wanted to get a small idea as to what to expect once i take it to the mech.

btw, on side note, can i get an emissions test done in order to get a better idea about the issue im having? i mean if i upload the data can the experts hear get a better idea? if so i can get it done within the next 24 hours.

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Posted (edited)
56 minutes ago, Niran gomes said:

btw, on side note, can i get an emissions test done in order to get a better idea about the issue im having? i mean if i upload the data can the experts hear get a better idea? if so i can get it done within the next 24 hours.

That wouldn't hurt. I sure as heck am not experienced to diagnose much using a emission report but there are experts here who could. 

But

it seems this could be narrowed down to one of these:

*Leaky gasket/valve stem seal (this is common and I have heard people mistake this for bigger problems)

OR

*Faulty O2 sensor

Take it to a mech and hope for the best. But something tells me the first one might be more likely. Since the Sonata are equipped with engines upwards of 2000cc, that could answer why you lose half a liter per month. What could have happened is this issue has existed for a while and has now ruined the catalytic converter and it might now need replacement like @Davy said.

This similar case happened to our swift and since its a 1.3L unit, oil consumption was there but way less than 500ml per month. But the smoke and smell was there for a long time of course. Changed the gasket, stem seals & oil after a week and is running clean!

 

Edited by □AVANTE□

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4 hours ago, □AVANTE□ said:

Leaky gasket/valve stem seal (this is common and I have heard people mistake this for bigger problems)

Okay, so before solving the trouble code... I've got to address the oil issue. I'll take it to the mech tomorrow. It's koreanLK i hope they'll do a good diagnosis of the problem., 

Just to further clarify, shouldn't a oil burning issue show it self with a oily spark plug end? Or rather a wet spark plug? And a head gasket issue showing itself again with a bubbling radiator and possibly engine oil in it? 

The engine is running super super smooth.... 

It might be my lack of knowledge probably. I'll get it checked anyway and let you guys know about the diagnosis.

 

Thank you for your valuable share of knowledge.

 

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16 hours ago, Niran gomes said:

Okay, so before solving the trouble code... I've got to address the oil issue. I'll take it to the mech tomorrow. It's koreanLK i hope they'll do a good diagnosis of the problem., 

Just to further clarify, shouldn't a oil burning issue show it self with a oily spark plug end? Or rather a wet spark plug? And a head gasket issue showing itself again with a bubbling radiator and possibly engine oil in it? 

The engine is running super super smooth.... 

It might be my lack of knowledge probably. I'll get it checked anyway and let you guys know about the diagnosis.

 

Thank you for your valuable share of knowledge.

 

You are right about the symptoms. It seems the gasket is fine then. I'm not sure about the spark plugs as I never checked mine during the issue. 

Get it checked, and let us know how it goes!

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