P0171 - System Too Lean (Bank 1)

[nasdamus]

Looking for some thoughts. 2003 V6. Keep getting a P0171 code. I pulled the MAF and cleaned it, same with the TB. Came back on after 10 miles. I checked all the vacuum hoses, all seems fine. I replaced the MAF with a known working extra i had, came back after 15 miles. Replaced the air filter (had to anyways), ran some Techron Fuel System Cleaner through a full tank of Shell gasoline. Took a little while to come back on but eventually did (maybe 45 miles).

5,000 miles ago I did replace all spark plugs as well as the PCV valve.

2.5 years ago (20,000 miles ago) i replaced the B1S1 o2 sensor (was getting a P2238 code) with a Denso 234-9047.

Any thoughts on what i should try next? Been searching around and checked most suggestions. I'm currently getting a real rough idle at stop, not stalling out but close.

 

[paperchasin]

Need more information, but I'm leaning towards a fuel system problem. Are you able to get fuel trim (both short and long term) info? Preferably for both idle and 2500RPM conditions.

 

[fullboogie]

Bad O2 sensor - change it.

 

[Hyfyer1]

I have the same 4Runner, and I'm currently getting P0171 & P0174....checked Vacuum hoses for leaks...all good. All O2 sensor were replaced 3000 miles ago, MAF & TB are fine....The vehicle intermediately bogged on upon acceleration.....Saw A video on this saying it could possibly be a clogged cat, putting excessive exhaust pressure on the engine. So I pulled my cats and noticed one was clogged, I cleaned it and now it got worse. The vehicle just has no pick up when pressing the gas. (Yes I replaced the Fuel Pump a few months ago) I'm going to drill out my cat to see if it remedy's the situation...I'll let you know.

 

[celicaben]

i'm having the same issues along with a misfire on cylinders 2-6, also getting "system too lean", and engine sounds like it's running on half the cylinders and bucks when starting out from a stop. i've replaced:
1. plugs
2. wires
3. coil packs and boots
4. pcv valve and gasket
5. mass air flow sensor
6. air filter (k&n cold air intake already installed, engine ran flawless on this for 10 years now)
7. put injector cleaner via fuel tank 4 times now each on a full tank of reliable gas.
8. o2 sensors (both done 10 k miles ago no issues yet there or codes)
what should i do next? i'm thinking its in the throttle body sensor and the idle air control unit. am i right or is it the injectors at this point? PLEASE HELP I NEED TO GET THIS FIXED ASAP

 

[pjku79]

Anyone resolve this? I'm having the same problem on a v8. Figure it might carry over.

 

[djpope09]

i'm having the same issues along with a misfire on cylinders 2-6, also getting "system too lean", and engine sounds like it's running on half the cylinders and bucks when starting out from a stop. i've replaced:
1. plugs
2. wires
3. coil packs and boots
4. pcv valve and gasket
5. mass air flow sensor
6. air filter (k&n cold air intake already installed, engine ran flawless on this for 10 years now)
7. put injector cleaner via fuel tank 4 times now each on a full tank of reliable gas.
8. o2 sensors (both done 10 k miles ago no issues yet there or codes)
what should i do next? i'm thinking its in the throttle body sensor and the idle air control unit. am i right or is it the injectors at this point? PLEASE HELP I NEED TO GET THIS FIXED ASAP

Did you ever solve this? I'm getting the fault and misfire on cylinder 1. I don't want to start throwing parts at it if I can help it.

 

[UrbanRunner651]

Was getting the code off and on for a couple months. Tracked it down to a crack in the header manifold. Replaced both sides with some JBA shorties and haven't had a problem since.

 

[djpope09]

Was getting the code off and on for a couple months. Tracked it down to a crack in the header manifold. Replaced both sides with some JBA shorties and haven't had a problem since.

How did you find the leak in the manifold? Was it pretty obvious?

Could you provide a link for the headers you bought?

 

[UrbanRunner651]

link?

On sale at URD, probably cheaper elsewhere or if you wait until black friday. Different coating options available.
https://www.urdusa.com/jba-headers-2035sjs-tacoma-05-11-v6-fj-cruiser-07-09-03-09-4runner-v6-tundra-05-06-v6-silver-ceramic/

I could hear a ticking/exhaust sound that wasn't normal inside the bay and eventually the crack grew large enough I could see it just from looking. It was a shitty weld on an aftermarket header for me but the codes are a pretty good indicator of a leak. You can use a cheap stethoscope without the end on it to listen to areas of the manifold and identify the leak. Or just bring it in to a shop for a quote and they'll find it for you.

 

[Jan777]

to summarize, the causes can be:

1. cracked header manifold
2. defect O2 sensor

Anything I miss?

I have the same symptoms and guess its the manifold, but before starting works I collect all the possible causes!

 

[djpope09]

1. cracked header manifold
2. defect O2 sensor

Anything I miss?

I have the same symptoms and guess its the manifold, but before starting works I collect all the possible causes!

I don't want to muddy the waters, but I'll add that I got this code after having a misfire on cylinder 1. It was misfiring bad enough to cause the too lean code. If you don't have a misfire I think your list is correct.

 

[earthrealm]

hmmm, lemme examine my manifold, as mine is only bank 2 , p0174

 

[81runner]

A lean bank on only one side can be down stream sensors, or it could be fouling injectors.

 

[earthrealm]

A lean bank on only one side can be down stream sensors, or it could be fouling injectors.

I THINK A CRACK IN THE MANIFOLD of that bank could also throw the CEL. lemme look at my oxygen sensor readings again , last time i checked, they looked fairly normal/within range

 

[earthrealm]

Need more information, but I'm leaning towards a fuel system problem. Are you able to get fuel trim (both short and long term) info? Preferably for both idle and 2500RPM conditions.

See my trims below


Freeze frame report generated by Torque for Android
=========================================================

Vehicle VIN: JTEBU14XXXXXXXXX
Vehicle Manufacturer: Toyota
Vehicle Calibration ID: 33535000

Freeze frame information:
------------------
Fuel Status = 0 byte
Engine Load = 15.686 %
Engine Coolant Temperature = 185 °F
Fuel Trim Bank 1 Short Term = -0.781 %
Fuel Trim Bank 1 Long Term = 12.5 %
Fuel Trim Bank 2 Short Term = -1.562 %
Fuel Trim Bank 2 Long Term = 38.281 %
Engine RPM = 613.25 rpm
Speed (OBD) = 10.563 mph
Timing Advance = 18 °
Intake Air Temperature = 111.2 °F
Mass Air Flow Rate = 3.98 g/s
Throttle Position(Manifold) = 16.078 %
Run time since engine start = 126 s
O2 Sensor1 Equivalence Ratio = 1.024
O2 Sensor5 Equivalence Ratio = 1.021
Distance travelled since codes cleared = 1.243 miles
Barometric pressure (from vehicle) = 14.504 psi
Catalyst Temperature (Bank 1,Sensor 1) = 869.72 °F
Catalyst Temperature (Bank 2,Sensor 1) = 869.72 °F
Catalyst Temperature (Bank 1,Sensor 2) = 264.2 °F
Catalyst Temperature (Bank 2,Sensor 2) = 264.2 °F
Voltage (Control Module) = 12.968 V
Engine Load(Absolute) = 16.078 %
Commanded Equivalence Ratio(lambda) = 1.005
Relative Throttle Position = 0 %
Absolute Throttle Position B = 47.451 %
Accelerator PedalPosition D = 16.078 %
Accelerator PedalPosition E = 32.157 %


End of report.