This is probably a dumb question but I have some confusion about the
O2 sensors on my 2002 Grand Caravan.  The books and articles I have
read say that since the early 1990's there are four O2 sensors for V6
engines.  One for each Bank before the catalytic converter and one
after.

In searching for the sensor, I can only find two.  Doidge has cleverly
placed the one I can find before the catalytic converter between the
engine and the firewall in order to make it as difficult as possible
to get to.  I did read an article saying that there is one in the
crossovedr pipe.  Unfortunately the front exhaust manifold and the
crossover are covered with a shield and I can't see much without
removing it.

Can someone tell me for certain how many O2 sensors there are and are
they located between the firewall and engine and at the catalytic
converter.

Thanks
Dick Finn