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Hi,
I’ve been getting a P0420 for some time now on my 2002 Toyota Sienna on and off but lately resetting the system will not make the code go away for long. I set up a custom list on my Actron ODBII scanner and took the car for a ride with the 3 o2 sensors. I am getting a constant 3.2 ish volt reading on my two upstream Air Fuel sensors while the downstream gives me a steady reading if about 0.6 V (which sometimes dips to 0.2 V). As it is it a Sienna, it has 2 warm up Cats that the upstream sensors are plugged into, and the downstream o2 sensor is of course after the third in-line exhaust cat. I have developed a small leak in the flange between the exhaust and the exhaust cat, if thisi has anything to do with the downstream reading.
Has anyone seen anything like this before? Are there any other tests I can perform?
Thanks!
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3.2V might be normal for those upstream sensors. They might be A/F or wide band O2 sensors. I don’t have enough experience with them except to say that you don’t look for or try to manipulate the signal voltage the same way you would that downstream O2. The only decent method I’ve ever found with them is to enrich or lean out the fuel mix and watch fuel trims for appropriate responses. I’m a little confused with where you’re saying that exhaust leak is at. But, if the leak is in front of any one of the O2 sensors, it could potentially cause theP0420 code. If the leak is well behind the O2’s, then it shouldn’t cause the code.
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