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Oxygen sensors, locations?

Posted By: WARBIRD97 On: 01-04-2008 @ 23:48:21         Reply | Edit
I am presently getting code for 420, since the car has 190,000 original miles, I started replacing the oxygen sensors, the parts store gave me 4 oxygen sensors 2 before and two after catalytic converter. My problem is I can only find one sensor behind the driver side catalytic converter, No where can I find a sensor behind the passenger side catalytic converter. Is there actually one their? Is there only three oxygen sensors?

It's pretty obvious where the two front ones are,

The car is a 1997 Trans Am LT1

Posted By: Injuneer On: 12-31-2007 @ 00:09:31     Reply | Top | Edit
P0420 = Bank 1 (driver's side) catalytic converter low oxygen storage.

Yes, your car has four O2 sensors, one on each bank before the cat, and one on each bank after the cat. Since the code is specific to the drivers side after-cat O2 sensor, why would you buy 4 new sensors? The code is actually for the cat, not necessarily the sensor.

Could be a faulty after-cat sensor on the driver's side, OR could be a faulty cat on the side, OR it could be a wiring problem on that side. You can swap the after-cat O2 sensors side-to-side. If the problem follows the sensor, its a faulty sensor. If the problem stays on the driver's side, its a faulty cat or a wiring problem.


Fred - 1994 Formula - 381ci / 275-shot N2O / TH400+GV
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Posted By: WARBIRD97 On: 12-31-2007 @ 00:23:57     Reply | Top | Edit
I did eventually find the fourth one it was covered in a little dirt near the transmission mount.

I thought, I would just go ahead and change all 4 sensors because the car has 190,000 original miles. I can definitely tell a difference in performance. Before when the car would turned 5000rpm, it felt like the motor was gaining and losing power, now she just runs straight up without any hesitation.

Unfortunately the catalytic converter is dead, a new one is on order.

I must say changing all 4 O2 sensors is not fun on these cars, and definitely not cheap.

Posted By: Injuneer On: 12-31-2007 @ 14:57:28     Reply | Top | Edit
Hopefully, you bought genuine AC/Delco sensors, from one of the online discount GM parts dealers.

Posted By: WARBIRD97 On: 12-31-2007 @ 16:25:35     Reply | Top | Edit
All 4 were BOSCH, Why?? nothing bad I hope..

Posted By: 97WS6A4 On: 01-02-2008 @ 08:43:48     Reply | Top | Edit
Unfortunatly, bad yes. The bosch sensors have a horrible history of being extremely sub par and lasting only a few months if that. Sorry to drop the bad news, but the money spent on the sensors will probably be wasted.
1997 WS6 A4, Flowmaster catback, K&N drop in, drilled/slotted rotors. 14.59 at 96mph, 2.121 60'. LT4 Knock Module, TB Bypass. More to come!!!

Posted By: HBHRacing On: 01-02-2008 @ 14:48:08     Reply | Top | Edit
With the exception of known good performance parts (IE MSD wires etc etc) all electronic pieces should be replaced with OE parts. Sensors, switches etc. Always.

But the 02 sensors have zero to do with a P0420 code. There is only a slight possibility, that the front sensor is reading slow enough to look like it's switching at the same rate as the front and trigger the false code. But it's so rare that it only works in theory, and in all my years I have yet to see it.

Want to confirm the cat is dead? Look at scan values of ONLY the front and rear drivers side 02 readings (the more data you look at the slower it reads) and watch the switching pattern. The rear sensor should switch from bias voltage ( anywhere above .450V to anywhere below .450V is considered a switch) about half as fast as the front. If they are switching at the same rate, the cat is dead.
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