Ok, here is what I learned.
The van has 3 sensors, 2 are A/F Ratio Sensor, mounted on exhaust manifolds, 1 is Oxygen sensor, mounted after the Cat.
Question is, which one is bank 1 sensor 1. I called many dealers, got contradictory info, some dealers say it the one close to the radiator, some say it's the one close to the fire wall.
And, even for the same dealership, different people told me totally opposite stories - the parts guy said it's close to the fire wall, the service manager told me it's the one close to the radiator and he said he is pretty sure there are actually 4 Oxygen sensors and I have to bring my car in so they can make sure which one is bad. Yeah, right, 4 huh, you either need training on the vehicle or you are just bullshitting trying to generate some revenue (he wanted to charge me $96 for just reading the code).
Well, from what I learned from the internet, I am pretty sure bank 1 goes with cylinder #1, which is the bank close to the firewall. So that sensor is called Bank 1, Sensor 1. The bank close to the radiator is bank 2, so that A/F sensor is called Bank 2, Sensor 1. And the Oxygen Sensor after the Cat is called Bank 1, Sensor 2.
Now, comes another problem, the parts dealer listed in their computer as B1S1 is actually B2S1 on my car. The part number is 89467-41011, this one has a yellow ribbon on the electric wire. The one on my car close to the firewall (B1S1) is 89467-41021 and has a green ribbon. The dealer I bought the part from is really confused. The parts guy said either their scheme is wrong or my car has the sensor installed wrong by the factory.