P0430 code ?

My sons car (2000 Trans am WS6) was brought home to me running about the worst i ever heard a car run. Very rough idle and very sluggish.He had been away at school and im not real sure about the driving habits.MIL was on so i ran the codes. I ended up with about 6 diff codes, random misfires, 02 B2 below threshold etc... I started running each of them down. I have replaced all plugs, wires and found #4 coil pack bad which i also replaced. Most of the codes went away after that except the B2 after CAT sen was still popping off a code. I pulled it out to inspect and it did have quite a buildup and film on it.A very dark color and not the white tiny like some i have seen. I went ahead and replaced both pre CAT and both after Cat sensors just to have a better comfort level. The car is running fantastic now and has a ton of power with no hesitation.All of the codes were erased. I have put about 45 miles on the car since the above work and now im getting this P0430 code (Catalyist Eff below thresh B2). This is the only code now. I delted this one and ran the car again for about 10 miles and the P0430 came back again. I was able to do the Drive Cycle Monitor on my Actron code reader and i do see variances that i dont understand on the 02 sensors. I was able to copy and paste the info below. Can somebody take a look and see what ya think. I hate having a ton of info and not knowing what i have or what to do with it. Thanks for any help i can get!

ST FTRM1(%) -0.8
Global OBDII

I/M Monitors

Since DTCs Cleared

Misfire Monitor ok
Fuel System Mon ok
Comp Component ok
Catalyst Mon ok
Htd Catalyst n/a
Evap System Mon inc
Sec Air System ok
A/C Refrig Mon n/a
Oxygen Sens Mon ok
Oxygen Sens Htr inc
EGR System Mon ok

=====================

DTCs (Codes)

P0430 MOD $10

Catalyst System Efficiency Below
Threshold Bank 2

---------------------

P0430 MOD $10

Catalyst System Efficiency Below
Threshold Bank 2

PENDING

=====================

Record Data

FRAME: -1 TM: -2.4

MIL STATUS On
ABSLT TPS(%) 0.0
ENG SPEED(RPM) 669
CALC LOAD(%) 1.6
MAF(LB/M) 0.64
MAP("HG) 9.7
COOLANT(°F) 225
IAT(°F) 97
IGN ADV(°) 17.5
SECOND AIR ATMOS
ST FTRM1(%) 0.0
LT FTRM1(%) 6.3
ST FTRM2(%) 0.8
LT FTRM2(%) 5.5
VEH SPEED(MPH) 0
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD
O2S11(V) 0.760
ST FTRM11(%) 14.8
O2S12(V) 0.770
O2S21(V) 0.755
ST FTRM21(%) 9.4
O2S22(V) 0.740
OBD2 STAT CA

---------------------

The rear O2 senders simply tell the PCM if the cats are working properly and have nothing to do with how the car actually runs. It is the front O2 senders that control fueling in closed loop operation. Chances are, either the sensor has failed or the converter has actually gone bad. Can you tell if the converter rattles or are there chunks of material being dumped from the exhaust. Our cars are known to have converter issues and they were replaced under an extended warranty program that has now expired. If you need a cat, there should be lots of used ones available as most owners have upgraded to aftermarket systems or deleted them with an ORY.

The data you posted appears good -- fuel trims are ok, it's in closed loop operation, but the engine temp is a little warm at 225 degrees. Just so you know, the dash temp gauges in our cars are about useless, so don't rely on them. The Bank 2 code means passenger side converter is the one having issues. You can't tell a whole lot from the narrowband O2 sensor data -- for the front O2 senders, it should cycle up and down rapidly. Around 450 mV represents stoichiometric A/F, but the reading will bounce between about 150 mV all the way up to 800 mV or so. Not exactly sure what the rear O2 sender data stream looks like as I have never checked it.

Thanks a ton PA, I can hear a little rattle but cant find exactly where its coming from. My first thought was the B side converter, thats where the after CAT sens had some build up on it. Maybe the multy misfires from the faulty coil pack that i replaced could have trashed the converter?? It sounds like the shield is loose but its not. Jr. said it had been running rough for awhile. And thanks for the heads up on the temp, i did find that odd as to what the gauge said vs the scanner read. 225 seems a bit warm.

I think the stock cats just go bad over time on our cars. We bought our car with 71,500 on the clock and looking back at its history I saw that the cats were replaced under warranty somewhere just north of 50,000 miles. Also, not a bad idea to clean the MAF with some spray CRC MAF Cleaner while you are performing other routine maintenance.

Thanks a ton bud!!! I really appreciate you guys and this sight when I need some help from time to time. I am going to replace the B side CAT and see what i get. I will follow up after thats done and let ya know the outcome.
Thanks again!

Glad to help! Let us know how you make out with it.

Driving around misfiring for a while will kill the catalytic converters. When the motor is misfiring you're dumping raw unburnt fuel into the catalytic converter.

also....if it's rattling it's probably about to self destruct internally. Not sure if you've ever had that happen but it will plug the exhaust up most likely and make the car a real pig. Had that happen on my truck a couple years ago towing a boat back from the lake. Thought I could just limp it home but no dice.....before I pulled over I had it floored and was doing 30mph. Once the temps started climbing I pulled it over about 2 miles from the house and had my wife bring me a hacksaw. :D

Sorry guys...not to threadjack or anything, but how do you know if you have a bad cat? Just the rattling and chunks of carbon in the exhaust? Will you normally throw a code if something is wrong?

I your rear O2 senders are functional, the SES may light up and an appropriate code will be set.

^^^

That and your car will run like poo. Just like Orion described in his post above. Once a CAT clogs up it's like cutting the air supply of on the front end of the intake. The motor just can't breath or in this case exhale.