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.

UPDATE: The pending P0171 fault after MAF sensor replacement has turned into an active fault.

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.

chapstick

OP, I'm trying to make sense of your log and find it a bit confusing since I'm used to vagcom. But from what I gather is that you have a evap leak which does not necessarily mean you have a full blown boost leak. The MAF was a feeble attempt and hopefully you didn't purchase a brand new Audi OE Maf. They are expensive, but at the same time I wouldn't buy anything less than from the makers of the that same Maf. I don't know why people go straight to the Maf - it's bit of a misnomer and Audi Mafs don't go bad easily. A well filter A4 will have a brand new condition Maf at over 100k miles plus.

My suggestion is to spend thirty dollars on a new N80 purge valve. They start to lose their seal and will give you evap codes after time. You need some wd40 patience and a very small right angle hose pick tool - home depot sells a cheap set made by husky that is a perfect fit. As for the N80, buy the Bosche model from ECS tuning. They are the makers of the Audi N80 model so Bosche is the TRUE oem of that part only cheaper. Hate the way parts manufacturers throw that term around and sell Chinese made parts. Autoparts buyers still don't have a clue about that these days.

If you do decide to try this make sure you do not break the plastic ninety degree connection that it leads to or you'll have a problem on your hands. Also have some small hose clamps ready to replace the small Audi clamps you'll be wrestling off. Be gentle and patient and use the tool and wd40 to get it off. I don't suggest you try to remove it dry - you're asking for that 90 degree hard pipe to break.

Note: if you want to check the N80 without swapping to a new one - I suggest you just change it for the better really - once you get it off suck(literally) as hard and tight-lipped and sealed around one end of the N80. If it's bad you'll notice that it just barely keep a complete seal and a barely noticeable amount of air will get through. Don't be stupid and not follow the flow direction btw. There's an arrow printed on and will point to the proper directional flow. Do not forget the orientation of the arrow when remounting the part.

Hope this answers your evap leak issue if it is one.

WifesTT

CaptainMandingo, did you replace the purge valve? Did it fix the problem?

Airbag

I don't think it has anything to do with evap , his system simply indicates not ready as he has reset the codes recently.

But op have you considered not enough gas causing your lean condition ? fuel filter or possibly dirty injectors ? just food for thought if you don't think it is unmetered air.