Replacing Catalytic Converters

[derekw7]

So my 99 Tahoe is throwing the P0430 code recently. I had the intake manifold gasket problem recently and it was replaced at around 128k miles (at about the same now). I am guessing that the cats should be replaced by now.

So here's the question: Any reason to replace the cats with something other than factory or OEM parts, like maybe with magnaflow cats? I live in CA, and I only know of Magnaflow making an OBDII, California-approved cat (about $430 for both cats from internet retailers).

Thanks

[J-Ri]

First off, I would start by replacing all the O2 sensors. I believe the reccomended replace interval is 100k, so you need them anyway. There is no replacement interval for a cat. Assuming the engine isn't running too rich, the cats should last until they rust apart.

If it does turn out to actually be the cat(s), I would go with aftermarket. We don't do exhaust work at the shop I work at, someone who does may have better advise here.

See also: "Crap!" in the "Silverado" forum.

[derekw7]

Is there way to test whether the cats are failing, as opposed to an O2 sensor issue?

[j cAT]

Originally Posted by derekw7

Is there way to test whether the cats are failing, as opposed to an O2 sensor issue?

when vehicle is put on a diagnostic machine it will chart out the o2 sensor voltages as throttle is varied. this gives a no guessing result as to what is bad, if the test were free it would be highly recommended , but this can be over 100.00 minimum to do. would you put your vehicle on this to see if your plugs were still good after 100.000mi? i don't think so. replacing the o2 sensors at 100,000mi is recommended and if not done you risk damaging the cats at 400.oo each. the o2 sensors cost 50-70.00 each. this is getting expensive so keep vehicle ,replace sensors, or buy new its up to individual i replace these o2 sensors at the 100,000 and i don't care if they will work to 150,000 mi i'm not taking a chance also gas mileage is effected..............

[J-Ri]

A 5-gas analyzer would be better. Looking at sensor voltages will only show what the O2 sensor is showing, so if it's bad, you're getting a bad reading. The 5-gas analyzer has a probe that goes in the exhaust and measures O2, CO2, CO, NoX, and hydrocarbons. But it would be just as much, if not more, than hooking up to the O2 sensors. So as j cAT said, just replace them. And replace them with GM parts. I bought 3 new O2 sensors for my Beretta and all 3 were bad, and they were a high quality aftermarket brand. If you try to take one back, I don't think you'd have a snowball's chance in hell of geting a refund. I was able to since our shop buys so many parts from this company, but someone walking in off the street would probably be stuck with it.

[MT-2500]

Originally Posted by derekw7

Is there way to test whether the cats are failing, as opposed to an O2 sensor issue?

One of the leading cause of cat codes is a cylinder miss fire or engine running rich.
How is your tune up end?

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

A little more info on cat code testing.
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.