CricketThomas

I recently got a 2006 accord with 140k, with all maintence done at a Honda dealership. So 12 days ago I finally get a chance to put some gas in it since it was given to me with about 15 gallons of premium fuel in it. I fill it about 4/5 full with 87 at the cheapest gas station in town (college student), I only tighten it to one click. I drive back and everything is just fine. I don't drive much all weekend and then Monday I take a short trip and after hitting the large grooves in a bridge the check engine light comes on, I freak out and take it to autozone where it spits out P0420, they clear it for me and i did some research and tightened the gas cap. The next (Tuesday) morning the light comes back on, Wednesday afternoon I start it after it sits for about 8 hours and the light is gone. Today, after I have about 1/4 tank, I hit the grooves of the bridge and about 40 seconds later I notice the light is on (unless it came on way before, (**** roads) I swerve pot holes all day). So I decide to go get some gas and get mid grade 89 octane and fill it and make it click about 4 times. Light is still on and I don't know if the car needs a new cat (not making any noises, car idles at 650 ish when warm) or O2 sensors.

The gas cap wiggles very little (maybe a 1/2 centimeter when wiggled) but it tightens fine.

So what do you guys think? Thank you for reading.

ekb16

iTrader: (1)

p0420 is a cat converter code replacing the cat should take care of it

CricketThomas

That wasn't helpful at all.

DCFIVER

LoL, what do you want us to tell you? Get a new gas cap?


He's likely right. Connect scan tool, monitor the fuel trim parameters, if they check out,replace the cat.


Period.

Japa

But...thats what the P0420 code means....

Could also be an O2 sensor...I'd probably start with replacing that first.

jonsey1886

P0420 can be thrown by any number of things:

Loose gas cap
Kinked/pinched wires from 1 or more Oxygen (O2) sensors
Failed O2 sensor
Loose/Damaged O2 sensor (you mentioned hitting a groove/pothole recently)
Clogged Catalytic converter
Damaged vacuum lines inside the engine compartment
INCORRECT FUEL GRADE IN TANK
Severely degraded spark plugs or Coil On Plug coils that aren't properly burning all the fuel.
Impurities in your fuel system (i.e. sugar in the gas, water in the gas, etc)

Start by finding the O2 sensors and ensure they are tightly secured and not visibly damaged. Then check the wires for visible kinks, pinching, tears, and other damage.

Tools needed:
Service Jack (NOT THE SPARE TIRE JACK)
Jack Stands
Ratchet w/ sockets in size 8mm, 10mm, 12mm, and 14mm
Specially sized O2 sensor socket for ratchet or an O2 sensor wrench
Flashlight or other light source
Needle-nose pliers or pocket screwdriver to remove any plastic clips holding the splash shield(s) under your car on

Estimated time: 1-2 hours

DCFIVER

These will NOT set a P0420.

These are unlikley to set a P0420


Otherwise the rest of your advice is fine for a DIYer who has time to waste......

CricketThomas

Thank you for the info, I'm going to check the service records and peak under the car to look at the o2 sensor. Do you think connecting and reconnecting the one located right under the center of the car connected to the Cat would have any effect(or re-securing it if loose) Also, since I posted this, the light went away. Then one morning it returned (tuesday), I hit grooves in the road (it stretches across the entire road, old college town) and it the next thing i know it was on. So maybe its a loose gas cap, (I smell no gas from when the cap is tight on the car) or maybe one off the O2 sensors is loose and gets jolted every time? Both times, the check engine light went away after driving 60 miles. I don't think it was me putting 89 in there, my family member put 87 in it since 2006, and her husband put top notch fuel in it whenever he drove it. I own a service jack, but i don't know how confident i should be when i put it under the jack point to resecure the O2 sensor (if its loose). i also checked the pressure coming from the tail pipe compared to 3 other cars (very large margin of error prob) and the pressure seemed normal.

And from what i can remember the O2 sensor has a small kink in the black plastic wire area under the car, i noticed that a while ago.

I think also think that my gas mileage is deteriorating, i filled up 10 days ago, drove 99 miles and the tank is nearly at 3/4!

DCFIVER

Stop wasting your time and save your money for a new cat.


A loose gas cap wlil not,in any way, shape or form,EVER set a P0420 code. I dont know where that moronic nonsense came from. But its false. The gas cap is not part of the monitor criteria.

Bad gas (not cheap gas,but rather gas with some abnormal crap inside) can push the cat to its catalyst limit and possibly set a code.


The code will set once the cat falls below 99% efficiency,meaning the window for code setting is very tight, and the light will come and go until the failure reaches beyond the threshold.

Modern mid to late OBD2 vehicles have strict criteria when it comes to a cat code. The PCM will test,retest, and then test again the oxygen sensor prior to setting a cat code.


Your O2s are fine. You need a scan tool to ensure the vehicle is in proper fuel control as this will affect the catalyst function. If it is in fuel control,replace the cat.

TyGuy88

I hate to be another bearer of bad news but DCFIVER is right. P0420 is due to catalyst below threshold. We see them all the time. The converter is going to need replaced and I wouldn't waste money on the cheap aftermarket ones. I have seen way too many go bad again after a year or two.

Easy Duzit

I know this thread is a few months old but I'm in the same boat. High mileage 06 Accord 4cyl (321k mi). Car is in good shape for all the miles and has never missed a scheduled maintenance but the CE light started coming on about 18 months ago. I drive a lot as a courier so when the check engine light first came on I finished my day (about another 150 mi) and next day brought it my mechanic. He's Honda certified and I've used him 20+ years so I trust him completely. On the way over to his shop the light went out. Told him it went out on the way over and when he checked the codes, he gave me the news and told me how much it would cost. He also said that I shouldn't worry about it until the CE light goes on and stays on, or if the cat starts making a rattling noise, that would also be bad.
I asked him if it could be the O2 sensor and he basically said on that year and model it's almost definitely not the O2 sensor. He told me a new cat comes with the sensors already attached and iirc he also said they're not made to be removed on this model (or maybe just that it's difficult to remove the sensor). So here I am 18 months and 80k miles later and the ce light still goes on for a bit and then turns off. It used to only go on every few months then eventually every few weeks. Lately I might go a few tanks of gas with no ce light, or it might pop on for a couple of hundred miles or so before turning off. Sometimes it doesn't come on for a week or so, (1000 miles +/- ). Is it possible that after so many miles it still has life left in it? My mechanic doubled down and still says I don't have to worry until the ce light comes on (0420 code) and stays on. Other then this one problem with the on again, off again 0420 code, the car has only once had an unexpected problem (when the starter gave up the ghost). Kind of hoping to get to 400k mi since it still runs great and has no leaks whatsoever but I really don't want to spend that much on a car with so many miles. I have to add about 1/2 qt of oil every 3000 mi. and my mech was impressed that I'm not adding more. So basically it's in good shape but what are my chances of hitting 400k?

-Easy Duzit

CricketThomas

thanks for the info, mine has been off lately for about a month or 45 days. It may have been the summer to winter fuel transition. I have also switched from off brand gas to the shell or Costco which are top tier brands.

jonsey1886

If you have access to a scan tool and/or DVOM you can check to see if the sensors are going or if it is indeed the cat. After determining which it is yes, you can remove and replace O2 sensors in that model, should you so choose.

2006 HONDA ACCORD 2.4L L4 Oxygen (O2) Sensor | RockAuto

Just make sure to use the correct sensors for your emissions setup-i.e. if you have a Cali or New York cat, you need to have 02s compatible with that emissions standard. They should be denoted in that link as either Federal or California.

Replacement cats can also be ordered

2006 HONDA ACCORD 2.4L L4 Catalytic Converter | RockAuto

And yes sorry about spreading the gas cap myth. It was something my local mechanic told me and now that I'm studying for my ASE (A1-A8) exams I know how false it is.