A clue to P0420 on 2002 Sienna in Mexico

Maintenance/Repairs
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1

I have had P0420 problems, usually in Mexico, with my 2002 Sienna. At times there is a failure, then it cleans up again. Strange.

Recently, it happened again, but this time there may be a possible clue.

It last failed, I think, last summer, and since then has worked perfectly.

I was driving to Tehuacan on a shopping trip and stopped at a convenient Pemex to fill up. Alas, they did not have Premium, so I had them put in 4 or 5 gallons of regular (Magna).

I drove maybe 35 miles to Sam’s Club, shut off, then moved the car to Aurrera (mini-Walmart), and went down town looking for a charger for my wireless phone. I drove the mile or two back to Sam’s Club, to pick up my pictures, then went home. A few minutes later, the Check Engine Light came on. P0420.

I drove back to my village, next day went and filled up with Premium. I turned off the P0420 and it hasn’t come on again, though I took a 200+ mile trip to Cordoba for a special birthday party.

It may be coincidence, but that CEL definitely came on soon after putting regular (Magna) in the tank. And, stayed off when I burned Premium again.

Here is something I learned last year. A cousin had told me that they sometimes have problems with regular, but never Premium. I thought that was weird, but bumped into a URL which told how Mexico gets its gasoline.

They send crude oil to Houston, then buy gasoline back from the Houston refineries. The premium gets its additives put in at Houston, the regular gets additives added in Vera Cruz when the gasoline gets back to Mexico.

Ah! Ha!

My current theory is that somehow they mess up the additives in regular, but not in Premium. I have no idea how this could cause a CEL, probably from a dirty cat. But, it was certainly an amazing coincidence if it wasn’t the gasoline. Any ideas or contrary opinions?

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@irlandes Yes, you may be right. Mexico has limited reliable refining capacity since the government syphons off nearly all of Pemex’s profits. I would not trust a PEMEX refinery to always put the right additives in. So, I would stick to Premium to ensure quality fuel.

I do like Pemex stations which are usually clean and attractive. The behind the scenes processing activities as something else entirely!

P.S. Not all the oil imported from Mexico is returned as gasoline. Most is used by the US market. This has given some posters the idea that the US is now a NET exporter of crude oil and products. It’s still a net importer to the tune of at least 5 million barrels per day.

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@irlandes: I don’t know if you have any emissions regulations in Mexico where you reside. If you don’t want to invest a lot of money in a 12 yr old vehicle with 200K+ miles on it, one option is to insert a spark plug non-fouler between the downstream O2 sensor and the converter.

It’s a very simple quick low cost procedure and the OBDII diags will be happy.
Just search for “spark plug non fouler trick”.

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One of the problems with the CEL system is that it’s not really “problem specific” when it comes to faults. My brother spent a lot of money trying to get rid of the pesky P0420 and a couple of other codes. The car ran good but the CEL bothered him so he spent good money trying to get rid of it. The money was spent but the repair shop did not fix the problem. I finally took a look at the little car and the first thing that I found was a very dirty air filter. I changed the air filter and cleared the codes. The CEL never came back on.

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They do have them, JoeMario, but as a temporary imported car it need not be tested. I don’t know if it would actually fail or not. It usually runs with no CEL, which is why i noticed it so promptly this time.s

The cousin takes his Yukon to be tested, and they always tell him it failed, so he pays $40 and then it passes. I have been suspicious, and last year, they told him it failed but made him fix it. So, my theory is they are not accepting bribery to pass a bad one, but faking a failure followed by a bribe, if you understand me. So, when it really failed, they wouldn’t take a bribe to let a bad one go.

Docnick is right on both things. The US only sends back part of the crude shipped to them. Sorry I did not make that clear. And, I do try to buy Premium, this was caused by a rare delay in their latest shipment. Still working fine and has since I think June.

And, they do take most of the GROSS sales, not net sales. You know from what happens in the USA, the politicians buy votes with that money, and the person who stops it is gone next election. They were really sweating it several years ago, since existing wells were running out and no money kept for further exploration. They are looking into permitting outside investment again. Or, maybe they have already done it, I am not clear.