P0420 on 2005 Sienna

[BearZDefect]

Friend has OBD code P0420 on their 2005 Sienna.

Reading suggests this is triggered by the upstream oxygen sensor bank 1 output being too similar to the downstream sensor output.


1. Assuming the wires are ok, is it safe to assume that the bank 1 upstream oxygen sensor is malfunctioning? If the downstream sensor or cat malfunctioned I imagine it would not specifically point to bank 1.


2. Is bank 1 the front of the engine?


Thanks!

 

[DrDusty86]

Miles?
In my experience when a Japanese car throws a P0420, the cat is toast, However, on Fords, Dodges, and Chevys it tends to be the upstream o2 sensor.

 

[bepperb]

Could be the upstream, downstream or cat. I think replacing the sensors will be a lot cheaper. I would start with the upstream bank 1 sensor if you don't want to pay someone to look at the realtime output of the sensors and make a more educated guess.

I believe bank 1 on the 3.3 is the firewall side. This might help:

http://www.toyotanation.com/forum/274-2n...eplacement.html

The 3.3 isn't as sludge prone as the 3.0 but the rear bank was the one that was a problem on the 3.0. Do you have high oil consumption?

 

[Quest]

mainly upstream (wideband O2 sensor) failure.

I've done my wifey's (04 camry LE) 3 yrs ago...been fine since.

Did my BIL's 02corolla (a year ago), all fixed up (no more P420).

I wouldn't haphazardly jump into conclusions that cat is toast. Afterall: with mild oil burning issues on my BIL's corolla (his own fault, irratic OCI in earlier days), cat still good and so is downstream O2 sensors.

Q.

 

[hypervish]

Originally Posted By: Quest
mainly upstream (wideband O2 sensor) failure.

I've done my wifey's (04 camry LE) 3 yrs ago...been fine since.

Did my BIL's 02corolla (a year ago), all fixed up (no more P420).

I wouldn't haphazardly jump into conclusions that cat is toast. Afterall: with mild oil burning issues on my BIL's corolla (his own fault, irratic OCI in earlier days), cat still good and so is downstream O2 sensors.

Q.


x2, usually it's an 02 sensor failure. Replace it and it should be good!

 

[DutchBrad]

My mechanic friend told me the P420 is set by the rear O2 sensor - behind the converter. That is on my 2003 Sienna. The cat efficiency falls over time, and when below 95% it sets the CEL on. He said the computer compares the emissions before and after the cat, and when the cat starts to loose effectiveness, it turns on that CEL. We don't have emissions testing here in West MI, so the light goes on and then I turn it off with my Scangauge.... I am not going to fix it. If you google P420 you will find it is a VERY common issues on many cars.

 

[Vikas]

Google Three Words:-

O2 Sensor Extension

 

[HTSS_TR]

Originally Posted By: BearZDefect
Friend has OBD code P0420 on their 2005 Sienna.

Reading suggests this is triggered by the upstream oxygen sensor bank 1 output being too similar to the downstream sensor output.

1. Assuming the wires are ok, is it safe to assume that the bank 1 upstream oxygen sensor is malfunctioning? If the downstream sensor or cat malfunctioned I imagine it would not specifically point to bank 1.

2. Is bank 1 the front of the engine?

Thanks!

Contact a Toyota dealer, Federal Emission Warranty is up yo 8 years/80k miles.
http://www.epa.gov/obd/420f09048.htm

 

[BearZDefect]

Thanks to everyone for the replies.

Sorry I did not provide some important information in the OP.

1. Total mileage is about 150k miles, well past any warranty.

2. This particular 3MZ does not consume a significant amount of oil.


As already pointed out, the upstream oxygen sensors are wideband sensors. They aren't cheap, so the idea of replacing one only to find it wasn't the problem isn't as attractive as it would be with a $50 oxygen sensor.

On the other hand, taking it to a shop would probably cost significantly over $300 if it is only that one upstream sensor. I won't even ponder the price of an OEM cat.

 

[artificialist]

Originally Posted By: DutchBrad
My mechanic friend told me the P420 is set by the rear O2 sensor - behind the converter. That is on my 2003 Sienna. The cat efficiency falls over time, and when below 95% it sets the CEL on. He said the computer compares the emissions before and after the cat, and when the cat starts to loose effectiveness, it turns on that CEL. We don't have emissions testing here in West MI, so the light goes on and then I turn it off with my Scangauge.... I am not going to fix it. If you google P420 you will find it is a VERY common issues on many cars.

The reason P0420 doesn't always mean a failed cat is because O2 sensors tend to react more slowly as they age. P0420 is set when the upstream sensor voltage is similar to downstream voltage, so if the upstream sensor is slow to react, but the downstream sensor reacts normally, it looks like a failed cat to the ECU.

This is why it is difficult to know if you have a failed cat or sensor. You could end up having to replace the upstream sensor(s), downstream sensor(s), and cat(s). That will get very expensive.

If there is no smog testing where you live, leave it all alone. If there is smog testing, you need to calculate how much your new parts are going to cost, and how much more life you will get from you van when you do all that stuff.

 

[Pete]

Denso replacement sensors are well priced on Amazon.com. You can determine the correct sensors at Densoaftermarket.com.

After replacing all 3 sensors on my 2002 Sienna, I've been fine (the van/cat have 175,000 miles).