2012 Honda Fit 120k miles.

Never had any issues, Changed tires few times and Breaks once. Have done regular oil changes, changed atf few times also replaced coolant at 100k. Had this car since new.

With covid-19 around it really isn't getting much use. I found cheap fuel and decided to fill up. The next day got a permanent code P0420.
I get this is a code for the catalytic converter but I am very much confused at which one and which sensor.

-------
engine -> header -> [1st cat + upstream o2 sensor] -> [2nd cat + downstream o2 sensor] -> muffler
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So, do I change both cats and sensors? Am I just throwing parts at it?

I was going to change the spark plugs during the lockdown and could easily get to the upstream sensor on 1st cat, is that worth it?

please advise

 

What kind of fuel did you fill up with (a name brand fuel like Mobil, Chevron,etc). My Fit will trip the same code if I use cheaper/non-name brand fuel. I switched to Mobil and it's been off for the last 4k miles.

 

This is a non brand, grocery store that has a fuel station. The thing is I've gotten fuel there for that last 6 years and never any issues.

 

Probably not a fuel issue, IMO. Don’t just throw parts at this and hope for the best. That code can be hard to chase down. Either you or a mechanic needs to do some testing. A couple of simple things you can do is when the car is cold try to shake or hit the cat converter and if it rattles interior parts have broken loose. If cat is clogged just take downstream O2 sensor out and see if driving performance improves. If it does need to replace the cat. Mechanic can also place a test gauge in downstream cat port and check for high pressure reading. Also check cat in and out temperatures, Outlet should be about 100 degrees higher. This link might help perhaps..
https://www.obdadvisor.com/p0420/

 

According to the '09-'12 factory shop manual "poor quality fuel may cause this DTC".. The question they ask is if there are any other trouble codes stored along with the P0420 code? Some additional codes they refer to are P0137, P0138, P0141, P0300, P0301-P0304. If more codes are stored, post them up here.

Since you state there has not been any problems to date with your car, you have had the car since new, and the miles on the car are low, I wouldn't start throwing parts at the car right now. Figure out a way to remove the suspected tainted gas or just drive the car and use up the gas.When you refill the tank, make sure to use some known quality gas. The rule of thumb for gas purchasing is to buy a brand name gas and from a station that pumps a lot of gas and stay away from the no-name brand gas and from a station that is less frequented and where the gas stays in the underground tanks longer. I would even go back to the station you last filled up at and ask if anyone else has complained about bad gas. The gas supplier could have advised the station of a problem with a gas delivery. Just a thought.

When you re-fill the tank, drive on the gas for a short time and delete the trouble code and see if it comes back on. By the way, you don't have to run any higher octane gas than what the owner's manual calls for to solve this problem. These engines were designed to burn 87 octane, and several sources state burning 89 or 91 octane is a waste of money.

 

It’s going to be a while before all the gas use used up with COVID-19.

I’m just getting p0420 code.

since I really can’t find a mechanic right away I’m just going to ride this out for little longer.

was looking for something I could do at home but it’s just guesswork. On top of that it’s hard to get under this thing, I’m just spoiled working on my truck where I don’t have to lift it go work on it 😄

I’ll circle back and update. Thanks all + stay safe.

 

I drove the car about 40 miles/day for ~3 days to run errands. The light went away.
Again it sat for 7 days with rain under quarantine. Just had to do a grocery store run and P0420 again.
Does sitting for extended time have anything to do with this?

Here are some images from my reader see if you guys can better interpret from these images.


Yup P0420

$21 Catalyst Monitor Bank 1, is this pointing to the upstream sensor?

Yup can't pass the test

Yup

Sensor only?

Heated Catalyst? Secondary Air System?


Any Thoughts?

 

I still stand by what I posted in post #5 here. It's still very possible that you still have bad gas in your car. You still haven't done much else since you originally posted here about the problem, and you're probably down to close to a half tank of gas now. So why not burn the rest of the tank and put some good gas back in it? That's the cheapest possible fix! We're in a shelter in place here in California also, but no one is going to penalize you for driving your car- so do it!

You can also look for a link on this forum for an original Honda Service Manual. Look up your trouble code in the service manual and follow the sequence of steps to diagnose your trouble code. As you read, you'll also probably read where the factory service manual states that the code could be the result of bad gas.

I wouldn't waste your money on costly sensors or catalytic converters until you rule out the inexpensive possibilities like bad gas. Good luck!

 

I agree with 56chevydan. Could be fuel.

I would do this to troubleshoot:
- Run the fuel down low.
- Dump a full can of SeaFoam in the fuel tank (yeah, the bottle says 1/3 can but we're troubleshooting)
- Fill up with a few gallons of premium (maybe two or three) from a good gas station
- Then drive it like you stole it.
- Wait for the fuel to run down low and fill back up with premium.
- If the CEL doesn't come back on, fill up next time with your fuel of choice and see if the code comes back.

If the code comes back on, those sensors are pretty cheap. Like under $50 since it's the secondary, downstream sensor. The Wideband upstream sensor is the expensive one. This secondary sensor is almost an on/off kinda thing. It reads rich and lean conditions and nothing in between. You can grab a generic one from Amazon. It doesn't need to be a Bosch, Denso, or an expensive name brand. This one isn't that important except for this CEL.

To replace the sensor:
- Rent the oxygen sensor removal tool from your local auto parts store
- Jack the car up on JACK STANDS (not a floor jack)
- Get a wrench that has good grip and see if you can remove the sensor. This thing might be baked on pretty good so having a wrench with a cheater bar might be helpful. You can try and use pb blaster but a propane torch might be more effective. This is why you need jack stands because you'll be moving the car trying to get this off.
- Replace the sensor. You may need to remove the windshield cowling to reach the wiring harness. I think it sits behind the throttle body and above the primary cat.
- Use some anti-sieze on the new sensor (should come with a tiny packet). Otherwise you can get a little packet at the register by the checkout counter of your autoparts store.
- Install the new sensor and make it tight plus a quarter turn if you can.

Hope this helps.

 

Yup this is exactly what I will do and update back.
I did originally plan to change the plugs, that is the only thing this car didn't get, I'm thinking of still doing this.

 

I am probably way off base, but did you check the gas cap? Reason I'm saying that is cuz my wife has a Toyota Camry & when the gas cap didn't fit like it was supposed to, we had a code that came on. Replaced the gas cap & that was it. Happened 2X. Has been OK for a long time.

 

1 can of sea foam before filling up with Shell V-power Nitro+

permanent code cleared after 50mi. about 80 miles driven so far

 

Thanks for the follow up, hopefully your cel stays off.

 

200 miles no cel. and car is driving normal, doesn't feel like is under powered. I will keep updating because I find this fascinating for some reason.

 

Be careful with additives like seafoam, they have been reported to damage O2 sensors and catalytic converters...

 

My car dash poped a check engiene light i drove right into a garage where we diagnosed a P0420. the first Mechanic said this could be a result of bad fuel. However the light din't go even after i added some premium fuel.
then i googled possible solutions and bumped into this forum. i got the most helpfull tips like cleaning the catalytic converter rather than buying the unit.
I cleaned my converter with the help of a mechanic friend and when we fixed it back the light was gone.
i would advise you to look for a profesional mechanic rather than doing it for yourself because the muffler settings in the Cat may are very sensinsive.
I wouldn't know the cost of this service abroad butin Nairobi it would cost you between 6 - 10 dolars or 1000 ksh

 

Hi, guys.

I got the P0420 for a while, i change and read the o2 sensor, change the spark plug, it doesnt change anything.

Finally i adjust the value gap, it look good and the p0420 gone.

had you heard the value sound?

 

Nope, at least not that I know of. Still going strong, no issues.

 

I got that code too, also PO302 cylinder 2 misfire. Im theorizing a misfire could dump raw fuel into the cat and cause the code; so Im in the middle of replacing the coil(s). just in here to see if anyone else has any ideas before I spend the money for the coils

 

Update. no code no nothing.
Recently notice if I drive this car for along time I can hear a low hum a bit of shaking. This happens every now and then and I can't figure out what this is. Spark plugs or timing related stuff?