P0420 -100.6% ST<FT 3

Asked by Apr 28, 2015 at 11:10 AM about the 2000 Honda Odyssey EX

Question type: Maintenance & Repair

I have a 2000 honda odyssey that has thrown a p0420 code.
My ODB when checking details related to code gave me the
throttle position @15% rpm 1426
MAP sensor
STFT1 -7.7%
LTFT1 -1%
STFT3 -100.6%
LTFT3 -100.6%

8 Answers

Also, gas mileage has dropped dramatically over the past 6 fill ups. 127 miles to my last fill up.


P0420 is a catalyst below efficiency code, it looks like your fuel trims are messed up, when was your last good tune up? Check you O2 sensors, see if they are switching properly and their voltage outputs are within specs.

I actually just had a tune up Friday. I wont be able to check the sensors until tomorrow. I am going to reset via battery and take a ride and check the fuel trim again. My CEL went off on its own so that info was my most recent Freeze frame since my last CEL and repair. I am a very new to working on cars. When my last car threw this code and my o2 sensors were bad it would idle funny and misfire. However my ONLY indication of a problem outside of freeze frame was filling up today after 127 miles for a full tank.

Check engine light came on for about 60 miles and went of as I pulled into my dads driveway to pick up the code reader.


Well at least you have a recent code now. Is the scanner capable of live data?

His is not, but I am at a friends getting it checked now. I'll post results as soon as I have them

My live codes showed no faulty o2 sensors. Front or rear. I Ran a can of sea foam thru the tank, seems to have increased my gas mileage back up to 221 a tank. On my tune up I just realized they did an oil change, visual check of hoses and fluids made sure nothing was mixing or leaking where it shouldn't be. My next culprit is ugly plugs. If I am headed the wrong direction please let me know. Even after sea foam and pcv replacement the issue it self is still existant. Now I have ruled out my o2 sensors it only makes sense to change the plugs. Idk. Any reccomendations and insight would be much appreciated. Ft3 was -89st -78.7Lt


If it went in for a tune up but only got an oil change but was charged for a tune up I'd be hoppin mad. I would have to say that you are headed in the right direction, check the air flow sensor and throttle body, make they are clean also. Just remember it still could be a catalyst failure, but you're engine needs to be operating properly before you can condem the cats.

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