Engine Light on, error Code P420

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Thread: Engine Light on, error Code P420

  1. #1
    crv|oc Rank: Member
    Join Date
    Jan 2009

    Unhappy Engine Light on, error Code P420

    I have a 2000 Honda crv, the engine light went on and I was told it needed a new Catalytic converter, It was replaced & things were good, when the light came on again they replaced both sensors in front of and behind the converter. I drove the car for one day and the light went back on, now I'm told more sensors need to be replaced. This is getting expensive, I think they're replacing parts hoping to find the problem. The error code is P420 if this helps. Does anyone know what's wrong?

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  3. #2
    cim is offline
    crv|oc Rank: Member
    Join Date
    Dec 2008
    The P0420 code is for low efficiency of the catalytic converter. This is basically set once the ECU performs a catalytic converter check and determines that the cat efficiency is low by looking at the seconday oxygen sensor output (after the cat) while inducing a rich condition for a small interval (during the cat monitoring test required by OBDII).

    Are there any other DTCs set? You should check for any other codes set (especially the secondary ho2s P0137/P0137/P0141) and resolve those before further diagnosis on P0420. I would also check the exhaust manifold, pipe and converter and look for any cracks or leaks which may through off this test or led to the cat failing.

    Also, what type of converter did you replace the old one with? Many aftermarket parts simply do not have enough catalyst to create a store of oxygen sufficient to pass the cat efficiency test (note that all manufactures set the level of this by their own specification and for the converter they designed for). You can get an idea of how close the value is to the threshold by looking at mode $6 data from a diagnostic tool and see what the current measured value was and the minimum threshold to set the P0420 code.

  4. #3
    crv|oc Rank: Member
    Join Date
    Jan 2009

    Check engine light

    Thank you for your input, it's a big help, the garage keeps replacing the sensor after the converter hoping to fix the problem. I'll give them a copy of your input. I think I messed up, till now the CRV has always been serviced at Honda but they wanted $2000.00 to repair it, a local garage did it for $750 but it hasn't worked out, guess I made a $750 mistake.

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  6. #4
    Join Date
    Dec 2008
    Before Checking a Catalytic
    Converter DTC
    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
    • 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 thermometer capable
    of reading up to 500°F.
    • If the outlet temperature is more than 100°F hotter
    than the inlet temperature, the converter is OK;
    clear the DTC, and return the vehicle to the
    • If the outlet temperature is less than 100°F hotter
    than the inlet temperature, replace the converter.

    This info comes directly from the service manual. Obviously your mechanic hoped that jumping to the end would solve the problem.

  7. #5
    MECP Audio Expert illegal's Avatar
    Join Date
    Feb 2008
    Northern Va.
    I bet the cat that was installed is junk. The dealer wanted so much money because the cat is that much more expensive. There is always a way to "fix" the problem with a o2 extender as well, but I'm sure the other guys on the forum wont appreciate me telling you about that.

  8. #6
    crv|oc Rank: Member
    Join Date
    Jan 2011
    I got the P420 .. no other codes stored ...

    It pass the emissions test .. I belive than the cat is good!

    I reset the EMC but 40 miles after the light comes on! ... then I reset the EMC again .. and 40 miles the light comes on

    I went to other emission test .. and it pass! ... Then I unplug both sensor and clean the conectors with electronic contact cleaner .. plug and reset the EMC

    ... No more P420

  9. #7
    crv|oc Rank: Member
    Join Date
    Dec 2016


    I have a 2001 CRV when I bought it I didn't know the engine light wasn't lit. I took it on a trip 7 days after I bought it and broke down on the return trip. It turned out to be the catalitic converter, It just so happened that I left my car in a parking lot of a auto service place (great luck). Because it was 5 1/2 hours from where I live I came home in a rental car. I decided to give them an opportunity to see what was wrong with the car, to my surprise they called me in two days, I got a great repair using Honda parts, and a great price from some really nice people in VA. I wish I had the name of the shop and the town right now, I would totally give them a lot of praise. Anyway, it has been running great, I went to the emissions test and they told me they couldn't test my car b/c the engine light is not on. Flashback to Va, the mechanic there noticed that the engine light was not on and told me some people turn them off to sell a car with it on. So now I have to find out if it, was in fact, tampered with. I have to keep paying for and receiving emissions tests, that my car can't pass, every month until I get it fixed or pay $450.00 to try to fix it AAAAHHAHHHA. Can someone tell me how to check the bulb? I am going to check the fuse first.


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