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

David Kavanagh dak at rochester.rr.com
Sun Nov 28 10:24:00 EST 2004

Is it really OK to just unplug the MAF? I've heard differing opinions.


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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