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Thread: HONDA SEZ:troubleshooting OBD II code DTC P0420

  1. #1
    Senior Member HondaSUV Elder 'Curly Q Links''s Avatar
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    Default HONDA SEZ:troubleshooting OBD II code DTC P0420

    Before Checking a Catalytic Converter DTC Oct '98 Honda Service News

    Before you troubleshoot an OBD II vehicle that stores DTC P0420 (67) (catalyst system efficiency below threshold), run these quick checks:

    1. Check for a leak in the exhaust system. If you find one, repair it, clear the DTC, and test-drive the vehicle.
    • If the DTC doesn’t come back, return the vehicle to the customer.
    • If the DTC returns, go to step 2.

    2. Connect the PGM Tester, and test-drive the vehicle while an assistant monitors the voltage signal from the secondary oxygen sensor (HO2S S2). After the catalyst reaches operating temperature, the HO2S S2 voltage should stay between 0.5 and 0.8 V at steady cruising speed. During deceleration, the voltage should be steady at 0.1 V or less.
    • If the voltage readings are OK, clear the DTC, and return the vehicle to the customer.
    • At cruising speed, if the voltage fluctuates or stays below 5 V, go to step 3.

    3. Measure the inlet and outlet external temperatures of the catalytic converter with a (laser) thermometer capable of reading up to 500F.
    • If the outlet temperature is more than 100F hotter than the inlet temperature, the converter is OK; clear the DTC, and return the vehicle to the customer.
    • If the outlet temperature is less than 100F hotter than the inlet temperature, replace the converter.


    ---------------------

    Curly suggests: If the catalytic reaction is OK, the computer is getting wrong info from your O2 sensors, often the secondary one. Do not replace it with Bosch. You can test / clean your O2 sensors with a common blow torch. You'll know right away whether to order a new one. 'propane torch method' is the keyword phrase to search.

    Last edited by 'Curly Q Links'; 03-10-2013 at 06:58 PM. Reason: clarity
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  2. #2
    Member HondaSUV Senior in training John Bennett's Avatar
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    I see PGM Testers and OBDII code readers for $50 - $120.

    If I'm going to invest that much money in an electronic tool, I think I would like to get on of those things that connects to a laptop computer because I think they will do more tests and monitoring.

    Curly, do you know anything about the laptop computer connectors and software? Do you recommend any one over another?
    Current Vehicles: 2000 CR-V, 1993 Accord, 2012 CR-V, 2003 Pilot

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    Junior Member HondaSUV junior in training mlane's Avatar
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    I don't know about the ones that connect to laptops, but I knew I didn't want to keep a computer turned on in the car. I ended up buying an ultra gauge http://www.ultra-gauge.com/ultragauge/index.htm. So far, I'm pretty happy with it. I can monitor the o2 sensors while driving.
    2001 CR-V LX AWD
    2004 VT1100C

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    Junior Member HondaSUV junior in training yankee dog's Avatar
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    I have vag com software that is for VW's (that I no longer own), however they do have some "generic functions" and I was able to visualize both o2 sensors functioning during various driving conditions on my laptop.

    The wave forms they produced were pretty interesting to see. Seemed text book function on the old sensors and very similiar readings on the new sensors. I compared my data with what I found on the net as far as what the voltages should be.

    Same P0420 code with old sensors and new sensors, similiar wave forms on the lap top. So my conclusion? Catalyst in the cat was all used up, or the cars computer had a higher standard than others for when a catalyst code was thrown.

    My solution was a $6 spark plug non fouler till I have an extra couple of hundred for a new cat. YD
    2000 CRV SE Clover Green, 140,000 miles and counting

  5. #5
    Member HondaSUV Senior in training John Bennett's Avatar
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    Thumbs up

    Quote Originally Posted by mlane View Post
    I ended up buying an ultra gauge http://www.ultra-gauge.com/ultragauge/index.htm.
    Cool beans! I know very little about automobile computer diagnostics. Sadly, this 2000 CRV is the first car I've owned that was new enough to have them.

    Last week I added a 2003 Honda Pilot to my family fleet of five Hondas. Now that I have two cars with On-Board Diagnostics, I want to learn more about this technology.


    Quote Originally Posted by yankee dog View Post
    I have vag com software
    I will check out the Vag Com software. I'm toying with the idea of installing a "Car Computer" in my 'new' Honda Pilot.

    I use a small Acer Revo computer hooked up to my bedroom television to play movies across my home network from my big computer in the living room. I love it.

    These little Acer computers run off 12 volts. They can be purchased on Ebay for $50.

    I think it would be cool to set one up in my Pilot that:

    * records video from webcams mounted in the front and rear of the car
    * displays continuous OBD-II information
    * plays my country music and metal MP3 files to the car stereo
    * does GPS navigation
    * serves as a back-up camera



    I could use that OBD connector when working on other cars I get in the future (my daughters are looking for new Hondas).

    I have a lot of learning to do.
    Current Vehicles: 2000 CR-V, 1993 Accord, 2012 CR-V, 2003 Pilot

  6. #6
    Junior Member HondaSUV junior in training yankee dog's Avatar
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    You don't want the vag com for a non VW vehicle. The only reason I used it was I had it left over from another vehicle that is now gone.

    You want to make sure you have the proper protocol for your vehicle. My 2000 honda uses ISO 9141, and so does chrysler and most european models.


    Get the software that covers the most protocols as it will make your software more versatile (cover more vehicles).

    Usually it is software and a certian data cable. Sometimes with certian types of dongle, based on who makes the software. Just do a little homework before you purchase and you should be good. Aloso get one that provides long term updates (for free preferred), so you can keep current with your software. YD

    BTW that acer is cool, gotta get me one!


    Quote Originally Posted by John Bennett View Post
    Cool beans! I know very little about automobile computer diagnostics. Sadly, this 2000 CRV is the first car I've owned that was new enough to have them.

    Last week I added a 2003 Honda Pilot to my family fleet of five Hondas. Now that I have two cars with On-Board Diagnostics, I want to learn more about this technology.




    I will check out the Vag Com software. I'm toying with the idea of installing a "Car Computer" in my 'new' Honda Pilot.

    I use a small Acer Revo computer hooked up to my bedroom television to play movies across my home network from my big computer in the living room. I love it.

    These little Acer computers run off 12 volts. They can be purchased on Ebay for $50.

    I think it would be cool to set one up in my Pilot that:

    * records video from webcams mounted in the front and rear of the car
    * displays continuous OBD-II information
    * plays my country music and metal MP3 files to the car stereo
    * does GPS navigation
    * serves as a back-up camera



    I could use that OBD connector when working on other cars I get in the future (my daughters are looking for new Hondas).

    I have a lot of learning to do.
    2000 CRV SE Clover Green, 140,000 miles and counting

  7. #7
    Member HondaSUV Senior in training John Bennett's Avatar
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    I will watch out for the thing about software updates and the most generic cable. Thanks for the newbie advice!
    Current Vehicles: 2000 CR-V, 1993 Accord, 2012 CR-V, 2003 Pilot

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    Senior Member HondaSUV Mentor
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    Surfing the internet, I came up with this:

    http://forum.e46fanatics.com/showthread.php?t=486937

    They talk about adding a spark plug non fouler to the downstream o2 sensor to get rid of the p420. What do you guys think?
    03 CR-V EX AT (England Built) 208k+ miles
    03 Element EX AT (Japan Built) 188k+ miles

    http://www.youtube.com/ajchien

  9. #9
    Senior Member HondaSUV Elder 'Curly Q Links''s Avatar
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    Quote Originally Posted by ajchien View Post
    Surfing the internet, I came up with this:

    http://forum.e46fanatics.com/showthread.php?t=486937

    They talk about adding a spark plug non fouler to the downstream o2 sensor to get rid of the p420. What do you guys think?
    Most importantly it's illegal, and there's two or three reasons why they made it that way.

    If a person can't get their vehicle to run right, preventing the diagnostic system from reporting the problem is not the cure.

    .
    '97 CR-V. . . . . . '00 CR-V SE (leather) . . . '98 Odyssey V-Tec ! !
    --------------------
    First, read the Owner's Manual, then SEARCH, your Internet is STILL WAY faster than mine.
    --------------------

  10. #10
    Senior Member HondaSUV Mentor
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    A year after reading this thread, I've got the p0420 also.

    Maybe half a year ago, I got the p0134. Cleared, came back a month later, and then I replaced the front o2 sensor. Fixed.

    Maybe 2 months ago, I got the p0420 during a rainstorm. I went through the steps above. No exhaust leaks. Secondary O2 sensor voltage checks out fine. 0 at deceleration, 0.64V at cruising speed. So I stopped. Yesterday during a rainstorm, p0420 came back. Checked the secondary o2 sensor voltage again today. It's fine again.

    So now what? Do I check the pre and post cat temp? Since the voltages are ok, I'm presuming the temp is ok. Is this an intermittently faulty secondary o2 sensor? If it is an intermittently faulty secondary o2 sensor, why don't I have a specific code for the secondary sensor?


    Thanks for reading!
    03 CR-V EX AT (England Built) 208k+ miles
    03 Element EX AT (Japan Built) 188k+ miles

    http://www.youtube.com/ajchien

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