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Hey guys – My daughter’s 99 Accord is showing the P0420 error, which indicates a probable bad Cat. In the past 6 months (+/-) it has come on two other times. Each time I’ve reset it and it stays off for another 2 – 3 months. My hunch is that the cat is probably border line? Maybe it’s an O2 sensor? I’ve watched Eric’s videos and others, and thinking it’d be best to go buy one of those infrared thermometers to check temp before and after cat. Am I damaging the car by clearing the error code? My theory was if something were truly failing and not be intermittent or borderline, that the CEL would trip on again much quicker than 3 months later. Thanks in advance for any replies. Also, this car has 238,000 miles on it. I just recently replaced all the motor mounts as they were broken. The transmission is really starting to slip bad in the first two gears, especially when cold, and I think I’ll need to replace the PS pump sooner than later, but need to confirm leak sources when weather gets better. Point is if I have to replace the CAT, maybe an aftermarket would be sufficient? Just now sure how much longer I can milk this car’s life but so far it’s doing great. Has zero body damage so it’s actually in really great condition.
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Your not hurting the car by resetting the code. We have had alot of posts for p0420
after an aftermarket cat was installed and never got rid of the code.[quote=”mx4cc904″ post=158449]Hey guys – My daughter’s 99 Accord is showing the P0420 error, which indicates a probable bad Cat. The transmission is really starting to slip bad in the first two gears, especially when cold, and I think I’ll need to replace the PS pump sooner than later, but need to confirm leak sources when weather gets better. Point is if I have to replace the CAT, maybe an aftermarket would be sufficient? Just now sure how much longer I can milk this car’s life but so far it’s doing great. Has zero body damage so it’s actually in really great condition.[/quote]
P0420 can be caused by a number of things from a loose gas cap to a vacuum leak to a bad O2 sensor. On my 98 Civic I had to replace both O2 sensors & and the gas cap which fixed the issue. Doesn’t mean your cat is bad. If you want a new one check out RockAuto.com for lower prices on OEM parts.
Check the O2 sensors per the FSM (link is http://www.hondahookup.com/forums/downloads.php?s=8256d3d0947a0ba1a897843ee82991cd&do=cat&id=4 ), check the gasket on the gas cap, check for vacuum leaks, pirate air problems, leaking IM or EM gaskets, etc
RE: The transmission run a can of SEAFOAM TransTune through the transmission and run the car at highway speeds for at least 10 minutes. While you’re doing that stop at the dealer & buy honda auto trans fluid (ATF-DW-1) or ebay/google for DW-1 transmission fluid if you’d rather. Auto trans takes 2.6 quarts and be prepared for the TransTune to kick a lot of sludge free. The older Honda formulation (ATF-Z1) was found to have a nasty property of sludging up after a few years so Honda changed it in 2010. Did this suggestion to mine about 2 months back & shifts wonderfully now at 196k.
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