P0420 on low-mileage 2000 Sienna

[CatNine]

I've read through the messages on this board, and I'm still confused about my P0420 problem. My 2000 Sienna has 78K, and we use it sparingly. The CEL came on 3 years ago, at 68K, and at the time the P0420 was accompanied by several other codes. I replaced the O2 sensor (B1S1) and found that the car started running rough almost immediately. Took it to the shop where they replaced both B1S1 and B2S1 sensors and told me that I actually have A/F sensors (they used Denso A/F replacements). The CEL came back on in a few hundred miles afterwards. This time P0420 showed up by itself. Last week I replaced the downstream O2 sensor (B1S2) with a universal one. The P0420 returned shortly after.

At this point I'm not sure what else can be done other than the catalytic converter. Everything I read here seems to point that way. Also what exactly is the difference between the A/F sensors and the O2 sensors? Are they only on California spec cars? I'm in NY state, but I did get the car used, could I have gotten a Cal car?

C

[Potter]

There's a sticker on the underside of the hood that shows what the car should have in the way of sensors. I don't recall how the codes break down, but it shows how many and what type of sensors the car has. You'll find decoding posted on this site somewhere, or google. It's reads 2AF 10 with some other seemingly useless numbers or something like that. They all mean something.

I had a P0420 and read somewhere about running fuel injector cleaning with Techron (mentioned only because that name was mentioned) on a few tanks of gas. It's makes the engine run hotter and may burn out contaminants in the converter enough to clear the code. Regular use of the product is not recommended. It worked for me, although the code is now intermittent.

Have also read that sensors should be the same brand, ie all Denso, for best compatibility.

Frustrating and expensive code, good luck.

[CatNine]

Originally Posted by Potter

There's a sticker on the underside of the hood that shows what the car should have in the way of sensors. I don't recall how the codes break down, but it shows how many and what type of sensors the car has. You'll find decoding posted on this site somewhere, or google. It's reads 2AF 10 with some other seemingly useless numbers or something like that. They all mean something.

Thanks, found them and indeed the car has the 2A/F on the emissions sticker. A friend of mine suggested changing the plugs, which I did, and reset everything. We'll see what happens.

[chuck's sienna]

Universal O2 sensors do not work well in Toyotas. The PO420 code is a strange one to me, and I tried everything to get rid of it. Finally I took the instrument cluster out and removed the stupid TPS bulb and the check engine light bulb; now it's fixed my way. BTW, a check engine light means "check emissions".

[Potter]

Removing the bulb may not be the best thing to do... the codes that can be displayed cover a wide range of malfunctions.

And if you need to get by a state emissions test, well, you won't.

[chuck's sienna]

Thanks yes I just passed Maryland's test last month as I got the light to go out for about a week using fuel additives. The test is every two years and my Sienna will be gone by then as it has 257,000 miles. If it starts running bad I'll scan it at home to see what's up. I sell scan tools for a living, among other tools as well.

[CatNine]

Originally Posted by chuck's sienna

Universal O2 sensors do not work well in Toyotas. The PO420 code is a strange one to me, and I tried everything to get rid of it. Finally I took the instrument cluster out and removed the stupid TPS bulb and the check engine light bulb; now it's fixed my way. BTW, a check engine light means "check emissions".

I'd love to do that, but we've got annual testing here in NY, so light or no light, the code will still be there. How do you know that universal O2 sensors don't work well in Toyotas? Should I try to get a Denso O2 sensor instead?

BTW, the misery continues: After I replaced the plugs, the CEL came back on almost immediately. The P0420 was joined by the P1130 (AF s1b1) code. I wanted to see if I possibly disconnected something while trying to change the rear 3 plugs, which were a bear to get at. So I tried to remove the sensor and swap it out with the s1b2. But it was frozen, despite 2 days of spraying with PB, and many attempts with various sockets and wrenches. It seems ridiculous that a Denso sensor should go before it's even 10,000 miles old. Any ideas here?

[ShawnM]

Low milage is probably worse for the catalytic converter. Short distance and infrequent driving never allows the converter to reach its normal operating temperature range and burn off the crud inside it. Fuel additives or a seafoam type treatment and a good blast down the highway may help flush it out again, but it depends on how bad it is. Most newer cars use air fuel ratio sensors now because they allow for more acurate fuel control. Think of it as going from a regular tv to a HD tv.

[Potter]

Originally Posted by chuck's sienna

Thanks yes I just passed Maryland's test last month as I got the light to go out for about a week using fuel additives.

Can you share which fuel additive worked for you? I got by inspection using Costo's fuel injection cleaner, I think it was made by Chevron. But the light came back on later the same day as we took it through inspection, and it's been sporadic ever since.

[chuck's sienna]

Just stick with the factory sensors, I don't know why the universal ones don't work. For a fuel additive I don't remember the brand, it was a common fuel system cleaner. Not ten miles from the emission test the light came back on.

[Potter]

Funny that the light would come back on for both of us just after passing inspection.

Wonder what the action is that causes it to go off while the cleaner is running through the car.

Have you noticed anything of concern driving with the light on, 0420 code active? I haven't.

[chuck's sienna]

Nope, been on for four years! Gas mileage runs 26 to 28 mpg so I know it's a happy engine!