2UZ p0174 hell

[soundmanlpte]

Been having a hell of a time tracking down an issue with these codes:

P0174: Bank 2 upstream lean
P0171: Bank 1 upstream lean
P2197: O2 Sensor Signal Stuck Lean Bank 2 Sensor 1

The Story:

This started about a year ago. Check engine light hit with P0174. But after I got gas, it didn't come back. I thought maybe some bad gas?

After 9 months or so, it came back with horrible exhaust smell and rough idle. So I changed the AF + O2 sensors on the passenger side (bank 2). That fixed it for a few weeks.

Then it came back, but this time it was P0171, bank 1. I thought, well maybe I should do the sensors on the driver's side. So I replaced both sensors there as well.

Same story, fine for a few weeks, then back to P0174. I've since tried cleaning the MAF, replacing the PCV valve, and running Seafood through the gas tank with no luck.

I do have a Scangauge. I punched in fuel trims. Short/Long hang around -3-8 until it gets fully warmed up, then it's like +20/45 respectively.

I think I'm down to injectors, fuel pump, or a vacuum leak. Is there anyway to narrow it down before tackling an expensive and time consuming repair?

 

[xtremewlr]

Some quick research on those codes gave me the following common issues to check for:
Vacuum leaks (Intake Manifold Gaskets, vacuum hoses, PCV hoses, etc.)
Mass Airflow Sensor (MAF)
Plugged Fuel Filter or weak Fuel Pump
Plugged or dirty Fuel Injectors

Vacuum leak should be fairly easy to check for. Just verify all vacuum related hoses under the hood are in good condition and not cracked or hard. Anything suspect should be replaced. There aren't a ton of vacuum hoses so that should be pretty easy. You should also verify that they are no intake manifold leaks at the mating surface from manifold to heads.

Otherwise, you are down to fuel pump or injector issues and should have the fuel pressure checked. It could be as simple as a failing/failed fuel pressure regulator, located on the passenger side next to the intake manifold on the fuel rail feeding the injectors and has a vacuum source going to it. Or a failing/failed fuel pump, clogged pump sock or injectors that are clogged and in need of a proper cleaning which involves removing and replacing or sending them off for a rebuild.

 

[soundmanlpte]

Thanks for the response. Would getting the fuel pressure checked help narrow down the issue? If fuel pressure is low, does that eliminate injectors as the cause?

 

[xtremewlr]

Thanks for the response. Would getting the fuel pressure checked help narrow down the issue? If fuel pressure is low, does that eliminate injectors as the cause?

Yes, it could potentially narrow down the issue. When you have that checked, they should be able to point you more closely to either a fuel pump related issue or injectors or potentially both.

 

[earthrealm]

intermittent p0174 4th gen 4runner

Been having a hell of a time tracking down an issue with these codes:

P0174: Bank 2 upstream lean
P0171: Bank 1 upstream lean
P2197: O2 Sensor Signal Stuck Lean Bank 2 Sensor 1

The Story:

This started about a year ago. Check engine light hit with P0174. But after I got gas, it didn't come back. I thought maybe some bad gas?

After 9 months or so, it came back with horrible exhaust smell and rough idle. So I changed the AF + O2 sensors on the passenger side (bank 2). That fixed it for a few weeks.

Then it came back, but this time it was P0171, bank 1. I thought, well maybe I should do the sensors on the driver's side. So I replaced both sensors there as well.

Same story, fine for a few weeks, then back to P0174. I've since tried cleaning the MAF, replacing the PCV valve, and running Seafood through the gas tank with no luck.

I do have a Scangauge. I punched in fuel trims. Short/Long hang around -3-8 until it gets fully warmed up, then it's like +20/45 respectively.

I think I'm down to injectors, fuel pump, or a vacuum leak. Is there anyway to narrow it down before tackling an expensive and time consuming repair?

any update on how you resolved this?...i have same intermittent p0174 and p0230 - which is fuel pump related, my full tank mpg has reduced to about 290 highway miles