2004 Tacoma Cat Converter Has 2 Sensors?

I bought a used '04 Double Cab Tacoma about 4 months ago. I'm now replacing what seems to be a defective front Catalytic Converter. The one on my truck now - the one that is bad - has TWO O2 sensors about three inches apart, both on the pipe BEFORE the converter. Is this odd? The Walker Cat I bought from Advanced Auto has only one port for a sensor...the upstream AF sensor (I think that's the right one).

I'm wondering if this cat converter (the broken one on my truck) has been modified to accept a second O2 sensor. Is that common?

Any help is much appreciated. I don't know if it is okay to just install the new Walker converter with only one senor without risking screwing something up.

 

I have a 04 double cab V6 and only one O2 sensor in front of the front cat. The FSM also shows just one in front of the first cat.

Do you have wiring for both front O2 sensors? That is the only think that may be a problem changing back to one sensor. What to do with the wiring for the other sensor?

Does one set of wiring look different from the rest? In other words, can you tell which is the original wiring?

 

Thanks for the reply.
Yes, there is a separate wiring harness from the additional O2 sensor.

These are the two sensors in front of the front Cat:
1.

$98 Denso Air/Fuel Sensor - 234-5002

http://www.amazon.com/gp/product/B00199FDAS/ref=oh_details_o01_s00_i00
2. http://shop.advanceautoparts.com/we...t-denso_20471798-p?searchTerm=air+fuel+sensor

I'm guessing the extra AF/O2 sensor has something to do with the aftermarket AF gauge that is mounted inside my cab, next to my shifter. It must be this that the wiring from the second sensor under the truck is going to.

My next assumption is that if I replace the existing Cat with the new Walker one (that only has the single sensor port), and remove the aftermarket wiring and AF gauge, I should be good to go.

Any opinions/thoughts on that?

 

The

$146 234-9001 Upstream Air Fuel Ratio Oxygen Sensor with 10.6” 4-Wire Harness, for Auto Trans Equipped Vehicles

234-9001 (your second link) is the Denso replacement for bank 1 sensor 1. That is the normal one.

I would try to trace/follow the aftermarket AF wiring to see where it goes. If it just runs to the gauge, then you are good to just yank the whole kit and kaboodle out of there.

If it connects to a wiring harness to get to a computer, then be more careful. Make sure once you disconnect it from the wiring harness that you seal it up. Don't just use electrical tape. Liquid tape for electrical works well and then if you want you can wrap electrical tape if desired.

If you have to take wires apart and have open ends, before connecting them, slide some shrink wrap on and then after connecting the wires back together, heat the shrink wrap over the connection.

Hopefully, it just runs to the gauge by your shifter. That will be easier.

BTW, if you ever have to replace the 234-9001, RockAuto is much cheaper than your link.

 

Bruce - thanks a ton on the advice. I'm pretty sure there's a wiring harness of sorts from the sensor to the gauge...but I need to take a closer look. But that's what I'd suspected.

Also thanks for the tip on RockAuto...just ordered the senor for 1/2 price of what I paid at Advance Auto - glad I kept my receipt

Have a good one...again, I appreciate your reply. It was really helpful!
Ken