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Discussion Starter #1
I just got a 2019 Frontier SV 4wd and it's my first 4x4. I went out for some very light wheeling, kept it in 2wd, and only used 4wd if I got stuck in 2wd which was only twice. I went through some mud/water but nothing like I see others doing online with their Frontiers so I didn't have much concern.

Well on the drive home it started a hard upshift and downshift going from 1st to 2nd to 3rd and back down, I couldn't get it above 40mph, and it was also hunting for idle. I was hoping I just got a sensor wet and just let it sit for 24 hours. Well after 24 hours it runs like normal, shifts perfectly, and is like nothing happened. No SES light came on the dash, but I had three pending codes: P0172 Fuel Sys-RIch B1; P0175 Fuel Rich-Sys B2; and P0101 Mass or Volume Air Flow Sensor "A" Circuit Range/Performance.

One of the main reasons I got a 4wd was for wheeling, but now I'm nervous to go off road if I can barely run it through some puddles without the truck going into limp mode.

What could I have possibly gotten wet to cause the issues described above? How can I prevent this from happening again?
 

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172/175 means that the ECM leaned the fuel mixture as much as permitted but the engine is still running too rich. I've seen it be caused by either leaking fuel injectors or a MAF sensor. Since you have both 172 and 175, I doubt that one fuel injector in each bank is leaking. And either way, they're pending fault codes; nothing is confirmed. I'd consider removing the MAF sensor and cleaning it with MAF sensor cleaner.

Correlation does not always equal causation. Heck, I've plowed my basically-stock Frontier through mud and muddy puddles that were up to the rockers and haven't had an issue. Engine compartment got sprayed with muddy water.
 

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Would a wet air filter result in the ECM leaning out the fuel mixture? Less air would require less fuel.
 
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Do you have a cold air intake? Do you have an oiled drop in filter?
 

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Discussion Starter #5 (Edited)
No cold air intake, regular paper filter, and the air filter was clean/dry. The engine compartment was surprisingly clean.
 
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