I had a nasty reaction to Lucas Ethanol treatment in my '11 Sport AT back in 2016. It may have been caused by a combo of fuel additives. I never got a Check Engine Light (CEL) / Error Codes but it put out a 'cloud' behind me, and noticed other cars would hang back when they normally would have been on my butt.

I had the misfortune of getting a whiff of this noxious cloud and it instantly 'stopped' me from finishing the breathe (involuntary response).

Not exactly sure of the origin of the orange colored material but it was a little 'gritty' and I used 0000 steel wool & WD40 to remove.

As far as I can tell, there haven't been any nasty side effects / no codes / 40k miles later but I'm not using that Lucas stuff again.

 

@fuego34 thanks for following up and posting updates. My CEL came on shortly after filling up at Costco. The P0420 code was set so I started researching what I needed to do. I'm going to follow your lead and burn through the gas and fill up at a different location next time. Then see if I still have trouble.
I did go ahead and buy a UV thermometer to check the temperature in front and in back of the converter. But mainly just because I wanted one of those thermometers to play with.

Thanks again

 

If you have an OBD2 reader/scanner with graphing abilities (amazon has some for around $30-$40)... test the two O2 sensors to graph their output voltages.

There is one before the cat, and a second one after it. They work together to help monitor fuel levels to the injectors.

The front O2 sensor should vary in voltage up and down once it has warmed up properly. It will always do this if it's working correctly (ie, toggling between lean and rich, over and over). If the cat is doing it's job, the rear O2's voltage shouldn't vary a whole lot... it should be pretty steady.

If the rear O2 sensor is going up and down like the front one, the cat may be bad/clogged/faulty.

There could also be a gasket leak between the engine header and cat where they connect (allowing outside air into the exhaust pipe), which would also trigger the 420 code. The gasket can get damaged if your exhaust hits a speed bump or a blown out tire/debris on the road.

This connection is just before the cat (2009 Fit for reference). It's similar for other gens.




Yes, it could be due to bad fuel, but considering how old the first and second gen Fits are, you may need to replace the cat. I would check with a mechanic before you go that route, that way they can do a full O2 sensor/system test with a much more detailed OBD2 reader/scanner.

Btw, if the rear O2 sensor is bad/dead (which would also throw the same 420 code), it would also not vary voltage (wrongly suggesting that the cat is working).

This may help some of you if you have a newer lower mileage Fit.... after a quick google search, in the US, Honda has an emission warranty for their cars... 7 years/70,000 mile's (whichever comes first). For Canada it's 3 years/60,000 km's (but I've also heard some shops say it's actually 8 years/130,000 km's for the cat itself). Anyway, if you fall under either of those things, the repair and parts are supposedly covered, but you have to get it diagnosed first (which costs a minimum of one hour shop rate).

Anyway, here is a good video explaining how to test/read O2 sensor voltages.

 

@PULOVR Really nice post! It's a pleasant surprise to see detailed information regarding diagnosis of emissions systems.

I'd forgotten to check and see if the code is still stored, but I believe I got the 0420 myself in late November. I do recall its reading out as o2 sensors picking up a lean condition at bank 1 on my Innova scanner.
Went ahead and adjusted valves, cleaned spark plug threads and re-torqued, and put some fuel cleaner directly into the injectors, brushed off their nozzles with a toothbrush.
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It wasn't the correct way to address the situation (in that emissions systems weren't tested or even inspected,) but did resolve the issue. I did check over the air filter, vacuum lines, and throttle body. Pretty much everything I could bang out in a hurry and for free.

Wanted to mention for others who may encounter this fault, that the cause of a code claiming issue with air/fuel ratio could be emissions damage or component/sensor wear/failure, bad gas, or engine stuff like dirty intake parts, spark plug troubles, vacuum woes, injector nastification, valve goopery/maladjustment.. If for example, exhaust valves don't open enough to let out the exhaust you could get a hot cylinder, and a hot cylinder may burn lean. Or if intake valves don't close good enough, you may get too much air! Air could even leak around the threads of spark plugs if they're loose. One or all of these things could contribute to an engine's development of a lean condition. So! if one should run through their own method of diagnosis and hit a wall there's likely more stuff to check out!
Additionally, the more stuff you go over and clean up, the better your car will run when the fault is finally resolved.

 

I may be new to the Honda Fit, but not to Honda cars and their associated chat forums (around two decades worth). ;-)

Anyway, it's just too bad that this forum has died down so much over the years (from what I can see), and that there are many threads with unanswered questions, and/or photos that have disappeared... photos that would really help answer some of the questions I and others may have.

 

This forum was slowing down before I got my GE. I'm pleased to say that hasn't impacted ownership for me yet.. The service manual for this car is outstanding.

The enthusiast in me has mellowed 😂 poverty being a key motivator.
When I can afford to have fun again, I'm getting a KTM 690. It will serve as my hobby and cause of death.

Tell yuh what. I may tackle the window motor/regulator assembly replacement soon. Maybe I can do a write-up for that. I'll have one window to screw up on and another to do show and tell!

Right now it's drum brakes on the tacoma, and good god it sucks Springs on those things are TOUGH! Then.. ford escape, wheel bearings.. tacoma, cylinder head, then fit.. and the freakin taco needs window assemblies too.

We may lack content presently, but the members here are class acts. When there's answers, they're typically pretty solid.

Edit: Also, it's a pleasure to have you here, dude!! I've been wrenching for a while now myself. uh.. not too long, started late. like 09. But am pretty darned active here!
​​​​​​​I wish my toyota problems could be addressed in this forum, as I'd much rather deal with you gents. That things manual is awful.