P0420 Code on 1999 Honda Accord EX

[4Runner03]

I have a 1999 Honda Accord EX 4DR and the CEL came on. I checked the ODB codes at Autozone and it came back with P0420 "Catalyst Efficiency Below Threshold." My question:

What is the next step in solving the issue. From what I have heard from research and mechanics is it could be the Catalytic Converter, O2 sensors, vacuum leak, and/or exhaust leak. Where should I begin? Any ideas would be greatly appreciated.

Thanks, Chris

[somick]

I did a Google search and here what I got:

http://www.google.com/search?hl=en&q...=Google+Search

It sounds like O2 sensor is at fault.

Sam

[somick]

Here you can see other points for troubleshooting:

http://www.obd-codes.com/trouble_cod...old-bank-1.php

Good luck,

Sam

[4Runner03]

Yeah I found that website also. I am now stuck with the problem of finding out whether it is the Cat converter or the o2 sensors.

Is there anyway to check if it is one or the other without having to replace one and seeing if the problem goes away?

[somick]

Your car is too young for catalytic converter. Actualy oxygen sensor is also not very old.
How many miles do you have on it?

On my son's 95 Accord LX oxygen sensor died at 140,000

Sam

[MT-2500]

Originally Posted by 4Runner03

I have a 1999 Honda Accord EX 4DR and the CEL came on. I checked the ODB codes at Autozone and it came back with P0420 "Catalyst Efficiency Below Threshold." My question:

What is the next step in solving the issue. From what I have heard from research and mechanics is it could be the Catalytic Converter, O2 sensors, vacuum leak, and/or exhaust leak. Where should I begin? Any ideas would be greatly appreciated.

Thanks, Chris

Always make sure engine is running right.
Engine miss is one main cause of a cat code.
If is bad and under 80K or 8 years the cat is under federal emmisions warranty.

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

Or a little on code testing below.

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.

[4Runner03]

Sorry forgot to mention that. It has 91K. The engine seems to be running perfectly fine. With what MT states for troubleshooting, I may just have to pony up the money and go to a reliable mechanic.

[MT-2500]

Originally Posted by 4Runner03

Sorry forgot to mention that. It has 91K. The engine seems to be running perfectly fine. With what MT states for troubleshooting, I may just have to pony up the money and go to a reliable mechanic.

Also if it is the cat.
It might be worth a call to Honda and see if they have any recalls or extended warranty on the cats.
Good luck
MT

[camaro383]

it is your Cat. that is a sign that the platinum inside the convertor is unable to do its job properly. Honda has a warrenty of 8 years/80,000 miles on exhaust. if you are a regular at the dealership...they might be willing to help you out.

[BIAR]

I agree with the above post.P0420 is a bad cat.An O2 would be a different code.Like was already said I would talk to the dealer they may help you.