I recently took my Fit on a rough mountain road that I thought wouldn't be as rough as it was and hit the undercarriage on a large-ish rock trying to clear it (the car plopped down on it and I heard a bang).

Now the engine light is on and the code pulled is P0171:

Powertrain System
produced primary trouble code:

P0171 System Too Lean (Bank1)

Looking up other posts I found the quoted suggestion above of possible causes for this code and was wondering does anyone have any idea which one would be most likely given the scenario mentioned above?

Other info: I'm not sure where on the undercarriage the rock hit, just that it is probably between the exhaust pipe and the front bumper, so anything in between. The code was pulled from a scanner from Autozone.
The car drives fine with no noticeable issues. Visual inspection of the undercarriage revealed no damage that I can see (just leaned under with a flash light and checked)

 

With a fuel code, yeah, Im wondering if you knocked the exhaust loose or damaged it/an o2 sensor. You may want to get the splash guard off and grab onto the exhaust and see if you can get movement out of it, see if anything is dented or damaged.
I appreciate your searching for the code yourself and providing a list. it helped :}
Air hoses n stuff are all up around the top of the engine and light in weight/flexible by comparison. I dont think it could be knocked loose by engine motion, but if you can't find an issue with the exhaust, feel free to check intake. i feel like its gonna be an exhaust thing..

​​​​​​exhaust trails all the way to the rear bumper as you know, and all kinda moves as one piece, floating on rubber hangers everywhere except where it attaches to the engine. Although the fit's exhaust is pretty neat and well organized, i'd be more suspicious of it because of location, mounting style, rigidity and weight both at the manifold and spread out across a long distance. A long metal multi-piece tube that's held together by bolts vs. flexible rubber boots, yuh know.
I've never experienced such a fault with the fit, but have seen it on an old straight six jeep. By design, its manifold stretched out away from the cylinder head much moreso than the fit, and its center of gravity was such that it wanted to flex where the six pipes came together into one to go down to the catalytic converters. It had developed cracks, likely as a result from poor design, then secondly construction materials, and the previous owner off-roading. This was verified by the fact that there were readily available exhaust manifolds for it made by multiple manufacturers, the majority of which were labeled as having a revised design and the plainly visible addition of flexible metal duct supplementing steel tubing at specific points. Heres a pic of the revised version, and I highlighted where I recall the cracks to have been on the OEM one.



I realize this isn't that, so im kinda leaning more towards the manifold or something coming loose instead. I'm hoping that's all it is. Does that sound reasonable?

 

Thanks, yes that makes sense. The only other thing I didn't mention is that I have a K&N filter installed instead of the stock air intake. I've read that if those get loose then that can cause the code as well, so with any luck maybe the jarring jolt from the hit knocked it loose and I just need to tighten it? Other than that it does seem likely that the hit banged up the exhaust pipe.

 

update:. There is a little hose with an open end underneath the air intake(my k&n filter) that had gunk clogging it up at the open end. I cleared that and the engine light went off, so maybe that was it? Have no idea what that hose is.


Other than that car drives great, fuel consumption is normal with expected mpg, no fuel leaking under the car.... This is not the first time I've gone off road with my Fit and remain impressed at what a little tank the car is

 

Sounds like we associated some things that weren't correlated after all. I'm still really curious to see how the fit's exhaust manifold would fail if it was subjected to excess motion, or if it would in any reasonable-ish environment. But looking at how Honda designed it, and how they suspended the engine, I think they did such an awesome job isolating. I'm happy to hear that you didn't wind up having a mechanical fault.

If you want to follow up, you can upload a pic of the formerly clogged hole, indicating its location as best as possible. May be able to tell you what purpose it serves. If it doesn't run to some part of the engine, it may be a simple drain for moisture or excess filter oil, whatever.

 

Yes I think it's a drain for extra fluid/oil. I have seen drops of fluid coming out of it before.

 

If you have an automatic transmission the open end tube you are describing sounds like the vent line for the transmission. It will get slightly oily over time and weep a small amount of transmission fluid. With that said I don’t see how your check engine light code and and that vent tube are related. Did you clear the code with a scanner or disconnect battery in order to reset the pcm or cel just went away without doing anything?

 

No I did not clear the code. I cleared that little hose of gunk and several hours later the light went off. Maybe it was a gas cap related issue which is also common as I did fill up not long before I saw the light. Could be coincidence that I hit that rock not long after? Who knows , these codes sometimes could be ten different things or more and are a mystery and a PIA to diagnose accurately. I'll keep an eye out for it coming back on though because I agree that seems too easy.

 

If you don’t have a code reader/scanner or access to one I would suggest just disconnecting the negative battery terminal. That will reset the pcm but keep in mind it will take several drive cycles for all the systems to display ready. So if you need an inspection depending on your state wait until it has say 100 miles or so.
Could be a gas cap thing perhaps. If that original code returns might want to take it to a good mechanic that has smoke machine and test for exhaust or intake leaks.

 

Thanks that's good to know and I am going to be keeping an eye on things. So far so good, no problems driving and car runs great.