99 Suburban 5.7 OBDII code P0430

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#1
??? Catalyst Efficiency Below Threshold (Bank 2) had within the last 11 mos replaced the Catalytic converters on this Suburban and now show this code. I think I have 2 Oxygen Sensors post the converters, how can I figure out which of the 2 are bad?
Thanks in advance for any guidance...
 
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#2
Code does not say replace or the cat or o2 sensors are bad.

How is the tune up.
Engine miss or runing rich is the leading cause of cat code?

http://www.troublecodes.net/articles/catfailure/

A little info on cat codes.
:)

DTC P0420, P0421, and P0430 & P0431: Check Possible Cause Of Misfire DTC P0420 and P0421 indicate bank one catalyst system efficiency is minimum requirement. DTC P0430 and P0430 indicate bank 2-catalyst system efficiency is minimum requirement. Possible causes are as follows: Use of leaded fuel. Oil contamination. Cylinder misfire. Fuel pressure too high. HO2S sensor improperly connected. Damaged exhaust system component. Faulty ECT sensor. Faulty HO2S. Ensure ignition timing is correct. Retrieve all Continuous Memory DTCs. If misfire code is not present, go to next step. If misfire code is present, isolate cylinder and repair as necessary. Check HO2S Monitor DTCs If DTCs P0136, P0138, P0140, P0141, P0156, P0158, P0160, or P0161 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. Check ECT Sensor DTCs If DTCs P0117, P0118, P0125 or P1117 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. If any codes except P0420, P0421, P0430 and/or P0430 were present in step 1), service as necessary before continuing. If no codes except P0420 and/or P0430 were present in step 1), go to next step. Check Rear HO2S Wiring Harness Turn ignition off. Ensure HO2S wiring harness is correctly routed and connectors are tight. Repair or replace as necessary. If wiring harness and connectors are okay, go to next step. Check Fuel Pressure Turn ignition off. Release fuel pressure. Install fuel pressure gauge. Start engine and allow to idle. Note fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to CIRCUIT TEST HC. Check For Exhaust System Leaks If exhaust system leaks, it may cause catalyst monitor efficiency test to fail. Inspect exhaust system for cracks, loose connections or punctures. Repair or replace as necessary. If exhaust system is okay, go to next step. Check For Exhaust System Restrictions Inspect exhaust system for collapsed areas, dents or excessive bending. Repair or replace as necessary. If exhaust system is okay, go to next step. Check Manifold Vacuum Install tachometer. Connect vacuum gauge to intake manifold vacuum source. Start engine and raise engine speed to 2000 RPM. Manifold vacuum should rise to more than 16 in. Hg. If manifold vacuum is okay, go to next step. If manifold vacuum is low, go to step 11). Leave tachometer and vacuum gauge connected. Start engine and raise engine speed to 2000 RPM. On a non- restricted system, manifold vacuum should quickly rise to normal range as increased RPM is maintained. On a restricted system, manifold vacuum will slowly rise to normal range as increased RPM is maintained. If manifold vacuum is okay, no indication of exhaust leak or restriction has been detected and testing is complete. If manifold vacuum is low or slow to respond, go to next step. Leave tachometer and vacuum gauge connected. Remove exhaust pipe from exhaust manifold. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is downstream from exhaust manifold. Reconnect exhaust pipe to exhaust manifold and go to next step. If manifold vacuum is still low or slow to respond, fault is in exhaust manifold or intake manifold gasket. Repair or replace as necessary and repeat QUICK TEST. Leave tachometer and vacuum gauge connected. Disconnect muffler/tailpipe assembly from rear of catalytic converter. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is in muffler/tailpipe assembly. Repair or replace as necessary and test-drive vehicle to verify elimination of symptom. If manifold vacuum is still not okay, fault is in catalytic converter. Repair or replace as necessary. Check tailpipe/muffler assembly for debris from catalytic converter. Test drive vehicle to verify elimination of symptom.
 
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#3
Crunch,
Obviously my diagnostic work is just beginning, you make an excellent point that the code doesn't isolate the problem to the O2 sensors. Since the only code that I'm able to retrieve are 4 separate P0430 codes 2 Bank 1s and 2 Bank 2s I will probably will need to look at the Fuel pressure since the harness and exhaust system itself seems free from obvious leaks and structural damage. I only A$$umed that since I didn't change the sensors when the Catalytic converter was changed that It would be that. I need to slow down and finish my root cause analyses before throwing more dollars at it.
I certainly appreciate the reply and will post the results of my finished diagnostic journey. Being "Old School/Shade Tree" and still trying to keep the family mobile, sometimes I feel like I'm in over my head, but that hasn't stop me yet.
Thanks again, you guys are great!!!
Bobby
 
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#6
I'm not sure what brand they are but they are the stainless with the 2 separate converters which came to about $400.00 vs the $850.00 the parts store or the $1,000.00+ the dealership was asking. To answer why the "Service Engine" light came on with a similar code before and wouldn't go off. That fixed it for 10 mos. Just this weekend the new code popped up , which I was able to clear yesterday afternoon, since I drove it last night roughly 75 miles the code has not reappeared. The code appeared this weekend as I was exiting the interstate after 5 miles of 70 mph. Again if it reappears I'll look for a miss fire code and start drilling from there. Last night I again had the opportunity for Interstate travel and no code popped up. My fingers are crossed.
Thanks again.
 
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#7
My (bad) experience on the newer 2002-up GM's tells me only the oem catalysts will work and not set the cat. codes. I am unsure if this applies to your 99 truck, but I suspect a smaller,cheaper catalyst won't do the job, not for long anyway. What causes this is the Oxygen storage capacity is just too weak on the smaller aftermarket cats. I can tell you Walker paid me two separate labor and parts claims for innefficient cats. I went OEM and had no more problems.