PO420 code on 97 tahoe

[blue chevy man]

Hi, I have a code PO420 on my 97 tahoe 4x4 with 140,000 miles. I've done the reading on the site and see that everyone pretty much says the converter is bad. Can it be anything else? I just replaced both converters with an aftermarket setup from CATCO that I purschased through summit a year and a half ago. Can it be that they've already gone bad? It's not affecting the driveability (yet) and everything else is in tip top shape. I've done a complete tune up on the tahoe. The 02 sensors are original.

Any help would be appreciated. Thanks.

[madness67203]

Originally Posted by blue chevy man

Hi, I have a code PO420 on my 97 tahoe 4x4 with 140,000 miles. I've done the reading on the site and see that everyone pretty much says the converter is bad. Can it be anything else? I just replaced both converters with an aftermarket setup from CATCO that I purschased through summit a year and a half ago. Can it be that they've already gone bad? It's not affecting the driveability (yet) and everything else is in tip top shape. I've done a complete tune up on the tahoe. The 02 sensors are original.

Any help would be appreciated. Thanks.

I had the same code with my 96 chevy astro van. I would take the after o2 out and see if it still heats up if it does. I would get the o2 simulator off of ebay that made my check engine light go out. the are like 22 bucks. It is a little black box with four wires coming out of it that u wire into the o2 harness. Or u could just try a new o2 after the cat.

[MT-2500]

Many thiungs can cause a cat code.
First check the tune upo condition.
Here is some info for cat codes.
DTC P0420, P0421, P0430 & P0431: Check Possible Cause Of Misfire DTC P0420 and P0421 indicates bank one catalyst system efficiency is minimum requirement. DTC P0430 and P0430 indicates 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(s) is not present, go to next step. If misfire code(s) 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. Ć 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 engineand 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.
Also here is a good link on cat codes.
Good luck MT

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

[blue chevy man]

Thanks for the input. I'll do some more t/s'ing to see what I come up with. About 10k ago I did a complete tune-up with cap/rotor, plugs, wires and have run some injector cleaner through it a few times since. It runs perfectly and shows no other codes except the PO420. I have checked fuel pressure and it holds according to the book. I have not checked for any exhaust leaks but don't believe I have any according to what I can hear. I will check the vaccum readings next. Is it possible that the high flow converters are tripping the code and I need one of the O2 sims or that I just have a bad post O2 on the left bank?

The vehicle also has a flowmaster muffler and dual tails from the muffler but I was getting the PO420 code prior to and after the installation of the flowmaster.

[MT-2500]

The pcm system is very senestive to what kind and how good of cats you have and also check the o2 sensors and 02 sensor readings real close.
Good Luck
MT

[blue chevy man]

Thanks MT-2500. I'm just not convinced it's the cats. I know a few people running CATCO's and they are having no troubles. I also had this system installed for a year and a half before I started getting the codes and it also started once it started to get colder outside (kansas). I'll try to get someone with a better scanner so I can monitor the readings on the O2's.

I'll keep you posted.