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

Al Adler adlere at sourcecodecorp.com
Sun Nov 28 13:25:32 EST 2004

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 

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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>>>>>> http://www.audifans.com/mailman/listinfo/biturbos4
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