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

David Kavanagh dak at rochester.rr.com
Sun Nov 28 13:32:22 EST 2004

Thanks. I did check for boost leaks (see this : 
I ended up replacing the leaking valve cover gasket. I haven't tried to 
re-pressurize the system since. I also wonder if it is really valid to 
pressurize at the point I did. I mean, the part between teh MAF and the 
turbo intake is generally under vacuum. Still, 10 psi can't be a bad 
thing to test with. If it leaks at that pressure, chances are I'd have a 
vacuum leak when running!
Thanks for the tip on CEL wrt. unplugging the MAF. My apponitment is on 
the 9th of December, so I do have time to drive it around.


Thus Spoke Al Adler:

> Yeah, if your fuel trims are that bad and the MAF is reading that low 
> it really does look like a MAF, especially since your're gettting the 
> multiplicative version of the Trim code - if you get the additive 
> version, its more likely a boost leak. One thing about the trim codes, 
> you'll need to drive a decent number of miles and cycle the car on and 
> off a few times to get the CEL to come back on after your experiment. 
> I made that mistake of clearing the codes and then not driving enough 
> myself and then took it to the dealer, they just said the MAF was 
> still ok. As soon as I got it home, the CEL was back and I just ended 
> up replacing the MAF myself instead of the time and hassel for the 
> dealer.
> As the other guy says do take a look for boost leaks. Given that 
> you'll be driving at altitude even a small one could be a problem for 
> the turbos and these cars should probably be checked for leaks at 
> every oil change. Given how shot your MAF sounds, you may actually 
> have both problems and the MAF is just covering the leak. I would wait 
> on the sensors until you see how the MAF pans out; some of them could 
> be side effects.
> Good luck
> David Kavanagh wrote:
>> 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!
>> David
>> 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
>>>>>>> _______________________________________________
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>>>>>>> Biturbos4 at www.audifans.com
>>>>>>> http://www.audifans.com/mailman/listinfo/biturbos4
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