Help with a code 420 on 2000 GLE

My Service Engine Soon light came on and Auto Zone read it as a code 420. The guy there said it was likely a catalytic converter going bad, said it would probably lose power as the weather warms up.

There aren't any real obvious symptoms. The only thing I can even barely notice is that it may not be idling as smooth as usual. It still has good power and acceleration and has 108K miles.

Anyone had one of these codes before? I'd appreciate any input. Thanks

My Service Engine Soon light came on ...

First reset computer(s) by taking batt off for ½hour. If error returns, start by voltage check, proceed by cleaning O2 sensor connectors. Cont., after readin http://www.cardomain.com/ride/748507/14

Also test O2 sensors with multimeter as FSM tells, replace if faulty.

...read also pages 10,15, 21 ...pick the info that fits u model.

Some say the cat has 8yr warranty. I dont know if its true and from which model... Check out from various sources, stealerships may (?) not want to know about that.

.

Thanks, Nahk.

Code 420 can be any number of things besides bad cat or 02.
First thing is check the tune up end.
Like 108K may be time for a tune up.

Cats carry a 80K and or 8 year manf. warranty and are replaced free of charge by dealers if in that frame.

Here is a link for 420/430 codes.
http://www.troublecodes.net/articles/catfailure/

Also some info on 420 code.
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.

Let us know how it goes MT

I've had that code set on my 2000 Max SE twice. It turned out to be nothing both times. There was no noticible difference in the way the car drove.

The first time I had it the dealer cleared it for me becase the car was within the 36000 mile warranty.

The second time it happened I just let it go and it went away 3 or 400 miles down the road. I believe it the car doesn't keep resetting it on you, ie. if it's a one time event, some mechanism clears it automatially whether it be ignitioin cycles or whatever.

Thanks for everyone's help. My light went out by itself so I guess that's good.

FSM explains that some events cause immediate service light. Others need multiple occurrence before light comes on. On some, auto-clear will come after repetitious runs w/o errors. Those 'runs' must contain certain 'elements': time, rpm, speed etc. As/if requirements are met, lamp goes off.

Theres a detailed logic chart of the setting events, drive 'map'. Fun to read those confuzean pages...

Had the same code on 2001 Max SE. Dealer put new pre-cat, and O2 sens's in bank one. If not under warranty would have been over $1k. Just one among many codes this car has puked up.