1998 Isuzu Trooper, 3.5L Automatic.

How many sensors are there in this year model?

I have checked underneath the truck and saw one before the catalytic converter, (3 wires), on the drivers side. Saw another sensor on the passenger side (4 wires)...

However, when I check partsamerica.com for this it shows :
<a href="http://" target="_blank">
http://www.partsamerica.com/ProductL...artType=291&am p;PTSet=</a>A

it says 2 each required for the upstream and 2 each for the downstream...

Where are the two other sensors located?

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There are 4 O2 sensors, 2 are in front of the catalytic converters and the other 2 are just behind the catalytic converters. They are about 12 inches behind them, hard to miss actually. Take another look.

I did and saw the other two....the passenger side''s PreCAT O2 sensor was way up and had to use a flashlight to see it. then the After Cat o2 sensor on the drivers side was hiding above a metal protector tab. I noticed it when I was on the passenger side angle.

Thanks....