New User: 2006 Audi A4 2.0T Fault Code P0171

[CapitanMandingo]

Hi all, I'm new to the forum. I have searched/read the threads on what to do about this code, but I was hoping I could get some back-up on my troubleshooting process.

CEL came on a week ago; rough idle, long starting time, etc. Used the BAFX OBD2 scanner and Torque App to pull fault code P0171 (System Too Lean Bank 1).

Put a new MAF sensor in, as it seemed the tests were showing O2 sensors good. After installing MAF, CEL went away, but after a few miles of driving, I got a PENDING P0171 fault with no CEL.

I have used the Torque App real-time data to look at vacuum (as I assumed this reading would help indicate if I had leaks). I am showing 23-25" of vacuum at idle, drops to around 5" with a quick throttle, then quickly rises back to 23-25" vacuum. So, I assume there isn't a significant leak. I also don't notice any obviously cracked hoses.

Since I have installed a new MAF, my next thought is a possible faulty before-Cat O2 sensor. My little knowledge of the O2 sensors is that there is one before the Cat and one after. I thought the before Cat O2 sensor gave loop feedback to fuel/air mixture system and the after Cat determined emissions/efficiency of Cat.

I also have a screenshot of a graph of O2 Sensor Volts for Bank 1 Sensor 1 and Bank 1 Sensor 2 that I will attach. NOTE: O2 Volts Bank 1 Sensor 1 seems to not be plotting?

I really appreciate any help I get. Thank you.


Data from Torque App is as follows:

Fault log report generated by Torque for Android
=================================================

Vehicle VIN:
Vehicle Manufacturer:
Vehicle Calibration ID:

Current Fault Log
------------------
ECU reports no current faults

Pending Fault Log
------------------
P0171: System too Lean (Bank 1)

Historic Fault Log
------------------
ECU reports no historic faults
Other discovered fault codes
(possibly pending, current or manufacturer specific)
----------------------------------------------------
ECU reports no other fault codes logged

End of report.

Mode $06 report generated by Torque for Android
================================================

Vehicle VIN:
Vehicle Manufacturer: Audi
Vehicle Calibration ID: 8E0

Test report:
------------------
MID:$01 TID:$83
- O2 Bank 1 Sensor 1
Max: 1.99882 Min: 0.3499
Test result value: 1.05725
PASS
----
MID:$02 TID:$07
Minimum sensor Voltage for test cycle(calculated) - O2 Bank 1 Sensor 2
Max: 0.44969V Min: 0V
Test result value: 0V
PASS
----
MID:$02 TID:$08
Maximum sensor Voltage for test cycle(calculated) - O2 Bank 1 Sensor 2
Max: 1.29906V Min: 0.44969V
Test result value: 0.86449V
PASS
----
MID:$02 TID:$81
- O2 Bank 1 Sensor 2
Max: 0.64514V Min: 0V
Test result value: 0.63538V
PASS
----
MID:$02 TID:$82
- O2 Bank 1 Sensor 2
Max: 1.29906V Min: 0.64514V
Test result value: 0.6549V
PASS
----
MID:$02 TID:$83
- O2 Bank 1 Sensor 2
Test incomplete or dependant test failed
--
MID:$21 TID:$84
- Catalyst Monitor Bank 1
Test incomplete or dependant test failed
--
MID:$3b TID:$82
- EVAP Monitor (0.090")
Test incomplete or dependant test failed
--
MID:$3c TID:$81
- EVAP Monitor (0.040")
Test incomplete or dependant test failed
--
MID:$3d TID:$80
- EVAP Monitor (0.020")
Test incomplete or dependant test failed
--
MID:$3d TID:$86
- EVAP Monitor (0.020")
Max: 0.07167 Min: 0.06954
Test result value: 0.07167
PASS
----
MID:$41 TID:$85
- O2 Heater Monitor Bank 1 - Sensor 1
Max: 1,239.90002°C Min: 754.90002°C
Test result value: 819.90002°C
PASS
----
MID:$42 TID:$81
- O2 Heater Monitor Bank 1 - Sensor 2


Screenshot of 02 Voltages and Equivalence.

http://imgur.com/rxCdgGF

[80sGuy]

I got the same code two months ago after replacing a brand new air filter and pollen filter. Code went away after a couple of days driving. Tests turned out fine from my Autel I/M Readiness. Usually the computer will store the code until you erase it. So long as you don't get a check engine light you'll be fine.

[CapitanMandingo]

I got the same code two months ago after replacing a brand new air filter and pollen filter. Code went away after a couple of days driving. Tests turned out fine from my Autel I/M Readiness. Usually the computer will store the code until you erase it. So long as you don't get a check engine light you'll be fine.

Thank you for your feedback. The only issue I see is that after I replaced the MAF, I was connected to the OBD2 port and scanning for faults. It initially returned zero faults, and only after some driving did it give the pending P0171 fault. So, I don't think the code reader is seeing an old code, though it may be.

[Sanjman]

Thank you for your feedback. The only issue I see is that after I replaced the MAF, I was connected to the OBD2 port and scanning for faults. It initially returned zero faults, and only after some driving did it give the pending P0171 fault. So, I don't think the code reader is seeing an old code, though it may be.

Your vacuum numbers sound like mine and I'm thinking we both may have a leak somewhere. I think it's time for a smoke test. I have everything I need to do it just haven't had the time :(

But others have replaced a PCV that had a leak, fuel filter, and many many have found a cracked hose. Also double check the n80 valve and the houses around it. Also look for oil spots / leaks.

Lots of shops take some carb cleaner spray and spray it on various hoses, to see if the motor responds to taking in the spray

[Eyal]

About the syatem too lean error, I would recommend N80 replace... solved my problem.