Hi scotty,
i have a p0420 code on my honda accord 2005 2.4 EX edition with 100k miles and manual tranny, car runs fine, no stumping, no jerking nothing, vtec kicks in exactly where it should come. On idle its smooth and steady around 700 rpm, when i go around the car i dont smell anything wrong with exhaust smoke that could indicate that cc is done and need to be replaced. I was scanning my car with live diagnostic option on my cheap obdII reader and i saw a short fuel trim is around 10% on idle ,and when i step on gas it goes down to 5-7% but when i let the gas it comes back at 10-11% again. I suspect its upstream O2 sensor (A/F) and the reading is wrong about cc.
Some diagnostic numbers:
o2s12 at idle 0.06-0.09v/ at adding gas its around 0.8-0.9v
o2s11 at idle -0.02-0.09mA (this is where i think its the problem is)
lambda11 0.970-1.02 (i suspect this is normal)
I would really appreciate another opinion, especially from someone who knows about honda's
Thank you.
P0420 is usually the CC. Usually.
When my O2 sensor went bad on my 1999 Honda Accord, there was another code that tripped. I don't remember the exact code number, but it wasn't P0420.
You could try switching the upstream and downstream sensors, and see if the data moves. If it moves, it probably a bad sensor(s). If it stays the about the same, it is probably a bad cat. The cat would need to be replaced.
I'd like to hear other thoughts on this...
Thy for reply, i heard that when cc is bad it would smell really bad especially coming from exhaust, the guy i bought that car from said cc was tested and it was fine, he recommended me to pour some additives in gas so it clears it out (the car was sitting in storage house for 10 years)...idk have u ever add additives in gasoline? and if u did which one u used (its aluminum engine)
on topic of o2 sensors i heard if heater is broken it will trip code for o2 sensor but if its clogged or wiring is bad it would trip 420 code...
I’ve never tried the cleaner thing. @yaser below has a good suggestion from Scotty, that is worth a try.
Scotty has some recommendations before replacing the Cat: use high quality gas, clean it with some paint thinner, remove the car and soak in dish washer detergent,...
