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

[Grant]

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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>
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