Question about 1999 Hyundai Sonata

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My engine light has come on in my HG 2003 Hyaundai. I went to have the code read, and it stated warm up calistic below thrust hold needs to be replaced. CODE PO431. Please help. I a, a female and know little about cars. Also do not make very much money. So far I have not tried to repair anything yet. Just need some avice. THANKS VERY MUCH

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I am very sorry to hear you are having this issue. The problem is that you have a plugged or partially plugged catalytic converter. The Catalytic converter is located in the exhaust system generally just after the exhaust leaves the engine. The converter is full of little balls made of palladium, titanium, and other medals. If uses these metals to hold some heat in the exhaust system and help burn off excess hydrocarbons. IT is a federally required emissions part so removing it is against the law. I would suggest that you go to a reputable exhaust dealer like Midas, or Car X and have them test the converter and replace it. This is a expensive repair, priced at Napa the original replacements are $460.00 each X 2. So it would be wise to have a muffler shop diagnose which one is the issue.

Posted on Aug 03, 2010


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Vapor Canister
See Figure 1

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If the canister is equipped with a constant purge hole, a small amount of air will pass into the canister.
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Fig. Fig. 1: Cross-section of the vapor canister

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Thermostatic Vacuum Switch
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  2. Start and continue to run the engine until the engine temperature increases above 122°F (50°C). The vacuum should drop off.
  3. Replace the switch if it fails either test.

purge valve location:


EVAP vacuum switch pic:


EVAP system diagram:

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