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Ron Z.
Ron Z., - Honda Tech -
Category: Honda
Satisfied Customers: 17782
Experience:  18+yrs experience. State Inspector and Honda Diagnostics
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2003 Honda Accord EX: research, this seems to be very common for Honda

Customer Question

My 2003 Honda Accord EX 5 sp. came up with codes P0420 & P0141. From research, this seems to be very common for Honda, unfortunately. But from what I read, there are certain causes for dealership said maybe I got bad gas??? I plan on keeping this car for a long time, that's why I bought a Honda, so if I don't know what caused the problem, how do I know it won't happen again. And is it absolutely certain that the cat has failed and not just a problem with the sensor? Car has 85K on it. Thanks in PA with strict emmission requirements.
Submitted: 5 years ago.
Category: Honda
Expert:  Ron Z. replied 5 years ago.

Welcome to! My name is DriveFast71(Ron) and I will do my best to answer all of your questions completely and accurately.


Actually- before condemning the Catalytic Converter- there is a Technical Service Bulletin that states the problem may NOT be the converter, but a software correction for the PCM (on-board computer). The P0141 is for the internal heater for the rear oxygen sensor. The PCM uses this heater to get the sensor to normal operating temps within a matter of seconds on cold starts. Before replacing the converter, I would suggest replacing the rear oxygen sensor, and having the Dealer check your PCM to make sure it has the correct software version installed. Clear the codes and road test the vehicle.


Here's the Honda TSB:


Honda Service News July 2004


S/M Fix: DTC P0420 Troubleshooting


2003-04 Accord, 2003-04 Element


The troubleshooting procedure for DTC P0420 (catalyst system efficiency below threshold) in the 2003-04 Accord S/M and the 2003-04 Element S/M is wrong. It was written before we had the current software problem and the updated software to correct this DTC. Make this change in your copies of the appropriate S/M:


Don't replace the catalytic converter unless the software has already been updated and DTC P0420 sets again; doing so wouldn't provide a lasting repair and could result in a warranty debit.

Ron Z. and other Honda Specialists are ready to help you
Expert:  Ron Z. replied 5 years ago.
  • Remove the secondary HO2S (A), and the covers (B).
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    Customer: replied 5 years ago.
    The dealership says the techs would have checked for any service bulletins for my car. since there is no misfiring or performance issues, they cannot tell me what is wrong and why it failed. Is that accurate? It seems a bit lame, especially since warranty expired 5K miles ago

    I cannot afford for this to happen again with a $1200 repair bill. Feel like I am stuck with this since I cannot pass my emssion inspection without it. And I have no ability to do the repair myself.
    Expert:  Ron Z. replied 5 years ago.
    If they checked the TSB's then they should have also checked the PCM's current software version, seeing as that what it states to do. The above TSB is straight from Honda. Unfortunately, there is nothing a DIY'er can do himself to checkl the software version- it will require a Dealer. My best advice, seek a second opinion at another Dealership. You can replace the Oxygen Sensor yourself- this is a fairly easy job. Might be a good idea to get the P0141 squared away, clear the codes and if the P0420 comes back, have the software version checked.
    Customer: replied 5 years ago.
    Thanks for your help. I'll give it a try.
    Expert:  Ron Z. replied 5 years ago.
    Glad I could help. Have a great day!