99 astro code po420

Hi - my astro now had this code for a while, thinking that it would be linked to engine miss problems (causing some bad emmisions) the O2 sensors did not like, but after getting a handle on the cap and rotor thing - once a year like it or not, my van now runs with no missfire log, but it still does pop up with po420 code. I am aware that it is a emmision code and that it points to the left bank O2 sensor or the sensor down stream (including the cat - brrr - 1 piece y pipe assembly - not cheap). But i was wandering if there is anything else that could cause this code to be generated. Thanx for any info on this topic. Andre.

Hi - my astro now had this code for a while, thinking that it would be linked to engine miss problems (causing some bad emmisions) the O2 sensors did not like, but after getting a handle on the cap and rotor thing - once a year like it or not, my van now runs with no missfire log, but it still does pop up with po420 code. I am aware that it is a emmision code and that it points to the left bank O2 sensor or the sensor down stream (including the cat - brrr - 1 piece y pipe assembly - not cheap). But i was wandering if there is anything else that could cause this code to be generated. Thanx for any info on this topic. Andre.

A code 420 is one of the most underdtood and hard to fix codes.
But one of the main causes is a bad tune up.
Always make sure your tune up is good and engine is running good first thing.
http://www.troublecodes.net/articles/catfailure/
And here is a little info on cat codes.
Good Luck MT
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.

you are the man, that is one detailed write-up and i thank you lots for all the information given, the only code that accompanied the po420 was a multi missfire code which definitly meant that i needed new cap and rotor, which by the way did get rid of all my missfire troubles, so i am left with 420. I did clear it, and it took about a day to return. Although i did notice that the van is sometimes really sluggish, feels really underpowered, i figure that i would give a fuel filter a try. Trouble is that it really is not telling me anything else, i have the obd2 explorer running on the laptop to see if i can capture what its trying to do. Once again thanks lots for your info.

you are the man, that is one detailed write-up and i thank you lots for all the information given, the only code that accompanied the po420 was a multi missfire code which definitly meant that i needed new cap and rotor, which by the way did get rid of all my missfire troubles, so i am left with 420. I did clear it, and it took about a day to return. Although i did notice that the van is sometimes really sluggish, feels really underpowered, i figure that i would give a fuel filter a try. Trouble is that it really is not telling me anything else, i have the obd2 explorer running on the laptop to see if i can capture what its trying to do. Once again thanks lots for your info.

Glad it helped explain it.
If you are losing power do the vacume test or have the back pressure checked.
The cat may be stopping up.
If under 80K or 8 years the cat is under federal emmision warntary.
Good luck
MT

Good Luck