[Biturbos4] HELP!!! Troubleshooting DTCs w/ EPC light

David Kavanagh dak at rochester.rr.com
Sun Nov 28 11:15:26 EST 2004

yes, I have the problematic Bosch unit (no yellow dot). It reads about 
107 (not 200), so my fuel trim is pegged at 25% and I get a constant 
CEL. I get these codes (only);
17536 - Fuel Trim: Bank 1 (Mult): System too Lean
           P1128 - 35-00 - -
17538 - Fuel Trim: Bank 2 (Mult): System too Lean
           P1130 - 35-00 - -

I have an appointment to get the local dealer to replace the MAF (since 
it is still under waranty). I'd just unplug to make extra sure of the 
problem. I don't want to get there and have them say "that isn't the 
problem, open your wallet".
So, I could reset the codes (which also resets fuel trim), then turn the 
ignition off, then uplug, then go for a test drive... if it feels 
better, it confirms the diagnosis. If still feels really crappy, then I 
don't know... codes at that point should show now signal from MAF (I 
assume)... sounds like a plan!


Thus Spoke Al Adler:

> Well, I've heard of it being done many times in the Audiworld list 
> without any direct consequences other than a CEL. Some people even do 
> drag runs with and without to see which is better. I've done it 
> breifly myself, the problem that I had is the connector was half 
> broken so when I reconnected I had an intermittent short that caused 
> havoc until corrected so I would take care getting the connector on 
> and off. Also the ECU is then using the MAP sensor and O2 sensors to 
> control the mixture so those sensors should be working. In your case 
> IIRC, the B1S1 and B2S1 sensors would be important to be working, I 
> think the seemingly failing B1S2 sensor would be less important since 
> its primary purpose is to monitor cat efficiency.  All in all I don't 
> think a short test on the MAF would hurt anything, and the refurbished 
> Bosch MAF's for the 2000's are below a $100 many places, including 
> even the dealer so its a good part to check first since the bosch 
> MAF's are very problematic.
> Al
> David Kavanagh wrote:
>> Is it really OK to just unplug the MAF? I've heard differing opinions.
>> David
>> Thus Spoke Al Adler:
>>> Two things - fuel trim codes can indicate a bad MAF. One thing to 
>>> try is to unplug the MAF and see if the car drives better. Secondly, 
>>> I believe B1 is the passenger side - I have a B1 S1 sensor on its 
>>> way out so I have done some research on the issue. Still, consult a 
>>> more qualified source before yanking parts. I would also check the 
>>> o2 and egt wiring, as was already mentioned. You seem to have a lot 
>>> of codes from the rear of the engine so maybe they'res some damage 
>>> back there.
>>> Grant wrote:
>>>> Ahh, something I have some experience with  ( I was about to write 
>>>> "know something about, but that may be overstating the case a 
>>>> bit....).
>>>> Let's start with EPC and what it is. EPC is "electronic pedal 
>>>> control".  The 00+ S4s are "fly by wire" cars which transmit pedal 
>>>> angle (from a sensor) to a throttle body stepping motor which in 
>>>> turn controls the butterfly angle and opening.  The EPC light 
>>>> indicates that your problem is within this system.  I've had the 
>>>> same gremlin and, at least, had the "pleasure" of chasing lots of 
>>>> false problems.
>>>> Given the above, I'd speculate that a large number of your codes 
>>>> (all the O2 and mixture stuff) are related to a different problem 
>>>> (probably O2 sensor).  But the last code:
>>>>> "17579 - Angle Sensor 2 for Throttle Actuator (G188) Implausible 
>>>>> Signal
>>>>>            P1171 - 35-10 - - - Intermittent"
>>>> Is exactly the one that I got (and occasionally continue to get).  
>>>> What it means is that the sensor sends back a butterfly angle that 
>>>> seems impossible given the throttle position, load, etc.  It can 
>>>> actually be either the pedal sensor or the throttle motor.  I never 
>>>> found out *for sure* the source of the problem, but I'd bet heavily 
>>>> on the following culprit, and I bet it will affect all of us sooner 
>>>> or later:
>>>> The scenario:
>>>> The throttle body is dirty.  The butterfly, as it wipes back and 
>>>> forth, slowly builds up a ridge of dirt in the throttle body, which 
>>>> the butterfly subsequently "catches" on - either in the forward or 
>>>> reverse direction.  I speculate ( as does on of Audi's regional 
>>>> training techs) that this is partially caused by a limited throttle 
>>>> angle in normal driving.  (e.g.: the car is very powerful and/or 
>>>> I'm a wussy).  If the butterfly rarely gets past this point, a 
>>>> ridge of fairly hard dirt builds up and you're on your way to 
>>>> trouble.  I got to the point where this happened daily, or at least 
>>>> weekly.
>>>> A new TB, Audi's suggestion (gee, thanks Audi) was $1000 + install, 
>>>> which made me hesitate and figure all the above out.  I did talk to 
>>>> several audi techs, but the only real proof I have is that I made 
>>>> the problem go away on my car and one other.
>>>> The solution has two parts:
>>>> 1) Move the butterfly through its motion several times.  In 
>>>> general, you get to have fun doing this part (yes, I mean go out 
>>>> and stomp on it - but the goal is butterfly motion, not engine 
>>>> revving, so high loads at low revs are actually best).  Make sure 
>>>> you move the butterfly through its motion and back several times, 
>>>> and do this on occasion just to keep it "swept out".
>>>> 2) If you can, get some gummout into the TB and clean it. The 
>>>> trouble here is getting access to the TB.  You need to remove the 
>>>> two snorkels that come up from he intercoolers, and one of them is 
>>>> a bear to get out, due to a snap-fit in a plastic track.  I'd hate 
>>>> to break something in there (maybe have your local, friendly garage 
>>>> do it).  If you decide to do it, you might look at the "throttle 
>>>> body boot replacement" instructions posted on the tech part of 
>>>> AudiWorld as a sort-of guide to removal.
>>>> I've had one recurrence after ~ a year, whcih was quickly exorcized 
>>>> by a deep exploration of pedal travel later that day.  Feel free to 
>>>> email me with questions, and don't panic.  Very likely its not 
>>>> $1000, but rather 2 hours, gummout, and a heavy right foot.
>>>> Grant
>>>> On Nov 27, 2004, at 9:39 PM, Adam Jansen wrote:
>>>>> As I was driving over the Cascades to visit family for the 
>>>>> holiday, the EPC light comes on the the power cuts out (not fun 
>>>>> coming up Snoqualmie Pass!)
>>>>> I dont have my Bently or family albumn with me, but luckily I did 
>>>>> have the laptop and pulled these codes:
>>>>> 17526 - Oxygen (Lambda) Sensor Heating: B1 S2: Open Circuit
>>>>>            P1118 - 35-00 - -
>>>>> 17522 - Oxygen (Lambda) Sensor: B1 S2: Internal Resistance too High
>>>>>            P1114 - 35-00 - -
>>>>> 16524 - Oxygen (Lambda) Sensor B1 S2: No Activity
>>>>>            P0140 - 35-00 - -
>>>>> 17866 - Exhaust Gas Temp Sensor 2 (G236): Short to Ground
>>>>>            P1458 - 35-10 - - - Intermittent
>>>>> 17536 - Fuel Trim: Bank 1 (Mult): System too Lean
>>>>>            P1128 - 35-00 - -
>>>>> 17538 - Fuel Trim: Bank 2 (Mult): System too Lean
>>>>>            P1130 - 35-00 - -
>>>>> 17579 - Angle Sensor 2 for Throttle Actuator (G188) Implausible 
>>>>> Signal
>>>>>            P1171 - 35-10 - - - Intermittent
>>>>> I am replacing the O2 sensor in the morning (driver's side rear 
>>>>> correct?) but I am worried about the Throttle Actuator and the 
>>>>> System running lean!
>>>>> I stopped when the light came on and then started off again as the 
>>>>> light turned off... it seems that the EPC light with the above 
>>>>> codes (expect the O2 sensors readings) come on only after the 
>>>>> engine has been running on the highway for 30-45 mins, which just 
>>>>> adds to the frustration of trying to fix it!
>>>>> ANY help would be appreciated!
>>>>> Thanks
>>>>> Adam
>>>>> 00 S4
>>>>> Spokane, WA but current stuck in Olympia and hesitant to crawl 
>>>>> over the cascades under limited power
>>>>> _______________________________________________
>>>>> Biturbos4 mailing list
>>>>> Biturbos4 at www.audifans.com
>>>>> http://www.audifans.com/mailman/listinfo/biturbos4
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