OK Folks, the codes were there before the tranny was worked on. I've done some additional research looking for a replacement direct fit cat in case I need it and came across Eastern Catalytic's website. They have some great info there. Apparently a healthy cat will have a varying O2
sensor voltage on the upstream side and a STEADY voltage on the downstream side like PawPaw advised. My doenstream side seems high on bank 2. Bank 1 downstream is switching high & low which indicates a bad cat. Still have the code for Bank 2 Sensor 2 Circuit malfunction and an evap
system large leak code which I believe is from the fuel filler neck which is rusted and I've patched with RTV several times. Time to buy a new one - are the sedan & wagon fillers the same? I'm having a herd time finding one specific to model at Rock Auto Parts. Same with the direct fit cat - the DOHC
engine has the AX4N trans yet the parts list AX4S trans. Any help here?
Thanks to all with their answers thus far
A couple of notes:
Beware of thinking the downstream sensor has a steady state voltage.
It does not. It varys depending on driving conditions in a more gentile
rolling manner. If you have a OBD2 Live scan tool, you can observe
Now if you see the same sharp transitions you see on sensor 1, that
usually means the cat is dead.
A word of caution here. If your harness has been damaged and
you have no connection to the secondary sensor, you may still
see a phantom voltage/waveform on the scan tool.
ON my 97, i have the bank one sensor 2 disconnected. On my scan tool,
i am seeing a sharper transition waveform on it. Obviously, its not
the sensor since no sensor is connected. Its a phantom voltage induced
into the wire harness. The key thing here is the level. This phantom
voltage only shows about .3V peak level on the scan gage. Thats part
of the clue that its not what it appears to be.
If your secondary sensors wiring has been damaged, and your reading
a low peak value on the post cat sensor, don't be so fast in condemning
Did you have any cat issues before the trannie work? if not, there may
be your smoking gun of cause and affect.
Be my guest if you want to replace your cats, but its an expensive
and potentially nasty job to do yourself if you have 15year old fasteners
and studs rusted so they won't move.
The aftermarket cats are marginal at best in many cases. And the OEM
level ones will make you think twice if its worth doing on an older car.
If i were you, i would make sure you covered all your diagnostic bases
before you bought cats.
It can be hard enough to remove the post cat O2
sensors. I have broke
and trashed at least two working on my bulls. You have little room to
work on the one under the floor pan even with the special bent handle
sensor remover you can buy. Sometimes, you need to heat them up
with a torch to get them to break loose before your strip the hex head
on the sensor