Toyota Repair: Toyota Sienna engine light, sensor signals, auto parts store

Question
I have a 2001, Toyota Sienna with a 3.0 L V-6 engine. It has 133,00 miles.

My probelm is I have gotten three different diagnosis from three sources for my engine light being on.

The dealer first said it was my Cat, but they tested in front and back and got the same readings. Then, they suggested blowing the fuel injectors, which they did. This worked for a month, then the light came back.

I had it tested by a friend, and he got a code 1135, which indicated "main O2 sensor malfunction".

I had it checked at an auto parts store, and they got code 1135, but said it was "pedal; positioning sensor" in thier book.

I checked with the dealer again. This time, they said it was code P0402 "needs updated ECU". That costs $1,100.00.

Can you help me nail down what the real problem is here? Thank you.

Answer
The engine ECU compares the 02 sensor signals to each other as well as making corrections to the fuel injection durattion.
If the two readings are the same, then the Cat coverter isnt doing anything. Then you get a p0420 code.
If you got a p01135 code then you need to change the o2 sensor.
Auto parts store is wrong.

Start with the o2 sensor, its cheapest and you need it anyway.

Mike