1999 sienna O2 sensors

[tanddy57]

Are all three O2 sensors the same type? I bought Denso brand O2 sensors from RockAuto and was told that they are the same. Changed all three but the Code P0420 still exists. Need advise before I change Catalytic Converter. Van has 179 K miles. Thanks in advance for any advise.

[SiennaCruza]

Only the bank 1 and bank 2 sensors are the same but the post cat sensor is different.

Denso would be the Toyota OEM brand. did you check MAF, Plugs, cables, ignition coils, as well?

[Potter]

I had a P0420 and cured it, seemingly, by pouring a jug of fuel injector cleaner from Costco (with Techron) into a half tank on two consecutive half fillups. Sounds nuts, I know, but saw it somewhere online and, knock on a keyboard, it worked.

Took it though state inspection a month early, which is when it went out, and it sometimes sneaks back on every now and then but most of the time is not present. I bought a scanner to check it's status, and for the fun of it sometimes check and the green light is on meaning it's good to go.

I almost bought a new converter, so glad this stuff heated the system enough to clear whatever was affecting the converter.