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

Al Adler adlere at sourcecodecorp.com
Sun Nov 28 11:02:59 EST 2004

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.

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
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