Hi all. Been getting an 02 sensor CEL. Codes are either P2A00, P0174, or both. Had the one it indicated replaced with an OEM part by the dealer. CEL came back on within 2 weeks.

When this first started I began smelling exhaust inside the cab when I used remote start. Shortly after that I got the first CEL. I had another dealer, then a private garage look at it. Couldn’t figure it out either. Yesterday, I took it to a reputable custom exhaust shop to check for an exhaust or vacuum leak. Mechanic said he was extremely careful/diligent but the tests reveal no leaks.

Car runs great as it always has. No loss of gas mileage or performance. No missing. No sputtering. Nothing except the CEL and the smell.

Anyone have any ideas? I’m at my wits end.

 

Changed maf, injectors, connector, manifold gasket, both upstream banks o2 sensors, plugs, motor mounts, vac hoses, and rubber filter neck. But it does run rich still. Also, did pedal dances. Not sure what else to do ...

 

that’s unreal. I don’t have much hope in figuring it out now.

 

Even changed dipstick thinking maybe getting air from there although improbable. Last thing to do is change rear 02 sensors and check voltages and grounds. Alil more info though, my maf does read higher than expected iat. Ive replaced twice with a Hitachi brand. Which is why I also changed the pigtail. But when I first bought the car it was in limp mode with abs/traction control lights bc of maf being faulty. I want to download nisscan3 but phone is too new according to play store. So yeah lol ...

 

I have fresh oil leaking from the rear valve cover gasket. It is flowing directly over the 02 sensor there that I replaced. I thought it was faint exhaust but it’s the oil burning off.

so I’m replacing both gaskets then seeing what’s up. If the light persists then vacuum leak test. If that’s good, then I’m replacing the MAF sensor.

if all that doesn’t work… I’m just driving it because it drives perfect and I’m still getting 25 mpg on freeway trips. And at least I won’t be smelling oil!

 

Mine runs well but runs rich ... get only around 200-250 miles a tank. Not sure how that compares. My instant fuel mileage avg 18 at 60mph and probably 16@ 70 mph.
Think i need to check fuel pressure, if too high the injector pulse would be too long for psi, theoretically, that should give more fuel in same time if pai was lower. Then again I have lean code and slow response on new o2 sensor; denso.
Ive worked at a dealership doing driveability back 2000-2002 but this one has me so far. Not having all tools needed doesn't help either. Used wds , Ford, test equipment then but now it's obdlink mx+
with best i can find app so far thats compatible.

 

yeah I get around 24-25 MPG on the highway. Prob 16 around town.

 

Damn, so im losing alot. I definitely can smell it rich.

 

Ok, so a couple things…

I got my leaky valve cover gaskets replaced. While doing so and putting it back together they noticed a torn Air Intake Hose Assembly (pic beliw). They surmised the leak of air after the MAF sensor could be causing the lean CEL.

Replaced it for $280 for the part from Nissan! 😏

Today, I drove it 50 miles on the freeway. First, let me correct what I said previously. While my car runs great, my MPG is down 4.5 mpg from my past normal. Guess I haven’t really had it on the freeway in a bit to notice.

secondly, my CEL came right back on after about 30 miles. So it’s not either 02 sensor, not oil getting into the sensor. Not the torn air intake assembly 😏

i think I’m just going to sell it. Not happy because I love the car but it’s evident after 4 shops no one has a damn


clue