So my check engine light keeps coming on and the code p0420(catalyst system efficiency below threshold) comes on, and on my navigation i have more codes which are p0171, p0174...any help on which parts need to be replaced?

 

the codes indicate a bad cat which can kill the o2 sensors.

so, you'll need to investigate the catalytic converter to see if it is bad. if bad, replace.

then see if o2 sensors fix themselves after cat replacement, if cat is bad.

if 02 sensors are still bad, replace.

 

Is it worth trying to replace the 02 sensors first? Im getting tired of this crap, its salvaged so the dealer wont inspect it so now i have to figure it all out by myself...and i also have u0155 any idea what that could be?:/

 

uh oh.
I googled u0155 and its saying the PCM/ECU.

when you reset the codes via battery terminal pull, which light comes on first!?
i'm betting its the p0420 which then throws the o2 sensors off.
so, replacing the 02 sensors first, wont fix the problems and will result in bad 02 sensors again

 

Yeah the p0420 comes on...so heres the problem...when my check engine light comes on i scan it and it gives me only 1 code which is p0420, then on thr navi it has some codes in the system but it doesnt show those codes on the obd2 scanner..are those the codes that the previous owner already fixed?

 

so, why was it salvaged?
water damage? or an accident?

 

I bought it after it was hit. It had a small front right damage..just a fender bender and replaced the wheel and bumper..so it wasn't anything Crazy, but all these damn codes i find in the navigatio "diagnostic info" area-_-

 

The p0171, p0174 are bank 1 and 2 are to lean. Most of the time that would be some type of air leak on the input or something in the intake. The p0420 can indicate that downstream cat is bad, or it could be an O2 sensor, or it could be an upstream o2 sensor or many other issues. But if you do and a intake leak and the ecu can not correct the air/fuel ratio and puts up the code you could burn out the CAT from the higher temps of being to lean.

I would first try to find my issue with the Po171 and po174

 

U0155 code Lost communication with Instrument panel cluster

 

the 02 sensors are connected to the cat.
so the cat is the main problem, not the 02 sensors, Arta.

 

I think there are three problems. CAT P0420, running lean p0171, p0174, and some type instrument cluster problem U0155. I have no idea on the U0155.

May concern is the cause and affect. I agree the cat sounds like it's defective, or maybe an O2 is not reading correctly, but has enough reading to test okay. But p0171, p0174 are saying lean, most likely an intake air leak. When an engine is running lean you are running hot and can burn up internal parts of the engine. My thoughts are that it has an intake leak and this may have burnt out the CAT. I would not change the CAT until I fixed the p0171, p0174, or you could burn out the new CAT, which the after market CAT manufactures don't cover under warranty. A defective CAT will not change the trim to the point, but will not change the trim to the point that you get a p0171, p0174.

My experience with catalyst system efficiency issues is fix the other issues first. Then figure out the CAT code.

The U0155 I don't think is related to the other two issues.

 

i got similar codes on my ol d99 Accord. kept trying to play funny games because i did'nt wnat to drop 600 bucks on a new cat.. finally ended up doing it and all the codes went away. I personally wouldn't bother wiht o2 sensors because if it does end up being the cat, then you're out 150$ for the o2 sensor..

 

I agree and would start with the cat unfortunately.

If you want to clear the codes stored in the nav, then follow this - https://acurazine.com/forums/audio-b...ed-nav-822769/

If the problem still exists, new/same codes will come back to the nav.

 

did you use an after market CAT or OEM?

 

OEM. Aftermarket has known issues with reliability with Hondas. they don't last very long.

 

My car had the p0420 light come on and off. Sometimes it wouldnt come on for a month and sometimes it would stay on for a month straight. I asked my mechanic about the spark plug defouler trick, bought the part and he installed it. It's been more than a year (20k+miles) and the p0420 code has NOT come back up again. Ask your mechanic about the defouler trick. Google it and show him what to do if he doesnt know..and if he doesnt know what youre talking about than you have a bad mechanic!

 

Theres a TSB for p0171 and p0174 reprograms the ECU

http://techinfo.honda.com/rjanisis/pubs/SB/B08-043.pdf



3G GARAGE
https://acurazine.com/forums/third-g...-016-a-613659/

 

defouler is a trick, not a fix. mechanics are taught to fix things. a band-aid is not a fix, and in some places (like CA) it won't pass emissions either..

 

^which points to the CAT.
Solved in post #2.

 

 

meow.