P0402 code

SONATABYALEX

MEMBER
2006 HYUNDAI SONATA
2.4L
4 CYL
2WD
AUTOMATIC
182,000 MILES

Above shown by obd2 scanner at auto part store. Want to verify that the catalytic converter is actually clogged up and not functioning.

Wednesday, April 3rd, 2019 AT 12:51 PM

5 Replies

JOETECHPRO

MECHANIC
705 POSTS

Hey SonatabyAlex,

Can you confirm is the code P0402?

Reason I ask is that P0402 is for excessive flow from the EGR.
P0420 is a catalytic converter efficiency code.

Regards, Joe

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Wednesday, April 3rd, 2019 AT 6:03 PM

SONATABYALEX

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3 POSTS

HI Joe,
I'm sorry, made a typo error. The actual OBD2 code is P0420 Hyundai - warm up catalyst efficiency below threshold Bank 1; this was from print out from AutoZone in January'19. After switching gasoline brand, the "check engine" light was off. Then two weeks ago in March, the light came back on. I tried the CRC brand injection cleaner, but the "check engine" light will not go out.
The car will start up without any issues. The engine runs smooth while in idle. Once in a while, I will notice the RPM's to fluctuate a slight bit. On the road, the acceleration is very good, ever since the injection cleaner, without any hesitation. There are no rattling noises coming from below. Transmission shifts smoothly [had the Hyundai dealer replace the transmission oil, too]. And gas mileage has not deteriorated.
Please pinpoint what is causing the "check engine" light to remain on, as I don't want to be replacing various parts as an experiment.

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Friday, April 5th, 2019 AT 8:44 AM

JOETECHPRO

MECHANIC
705 POSTS

Hey SonatabyAlex,

If you have only the P0420 code and no other Engine management related codes you will need to:

Check to ensure there are no exhaust leaks.
Check the O2/AFR sensors are reading correctly. The before catalyst should be switching from around 0.15V-0.85V. The after catalyst should be a steady reading around 0.6-0.7V. If this after catalyst sensor reading is not steady it indicates an inefficient cat.

If you have no exhaust leaks and sensible O2/AFR sensor readings then you will need to replace the catalytic converter.

Catalytic converters do degrade with age and with the mileage you have it is not unusual to need a replacement catalytic converter. There are catalytic converter cleaning products that you add as a fuel additive you could try but you may still end up having to replace the converter anyway.

Hope that helps.

Regards, Joe

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Friday, April 5th, 2019 AT 10:36 AM

SONATABYALEX

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3 POSTS

Where would I check for exhaust leaks? At the tailpipe? Is this a visual check?
The car has 182,000 miles.
How much should I expect to spend on new catalytic converter?

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Friday, April 5th, 2019 AT 8:17 PM

JOETECHPRO

MECHANIC
705 POSTS

Hey SONATABYALEX,

The main area you are looking for leaks is before the catalytic converter or just after.

It is easier with the vehicle on a hoist so you can listen and access the areas with the engine running.

Catalytic converters vary in price by quite a bit.

From $200 up to $800 depending on quality.

You do get what you pay for generally and depending on if you are expecting to keep the car long term it may be worth sticking with Hyundai parts/ a reputable OEM manufacturer.

Hope that helps, worth a bit of a search to see which parts people have had good experiences with. I would advise to stick to mid-upper price range parts from a well known manufacturer.

Regards, joe