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

Michael Benno mbenno at yahoo.com
Sun Nov 28 21:42:13 EST 2004

Please keep us informed of what you find out. 
I personally agree with Grant, that your problem lies with the EPC system (Throttle Plate). Incorrect position could be causing mixture condionts that would cause your O2 sensors and EGT senors to be throwing codes.
Maybe this will help. I pull this from the self study guides. If your running condition sounds like either of these then you may be in an emergency running mode. HTH...
Mike Benno
A6 2.7t

Self-diagnosis/emergency running

If a fault occurs in the accelerator position sender or the wiring, two emergency running programs can be run depending on fault type.

Emergency running program 1: If an accelerator position sender fails:

• Accelerator position limited to a defined value.
• If a full load is predefined, the power output is increased slowly.
• In the case of implausible signals between G79 and G185, the lower value is used.


The idling speed position must be learnt once by the intact sender.
• The signal supplied by brake light switch for brake pedal switch F47 indicates the idling speed.
• Comfort functions (CCS) are prohibited.
• The fault lamp for electric throttle control K132comes on.

Note: At idling speed, the accelerator position senders G79 and G185 are not diagnosed. If the plug of the accelerator position sender drops off, no fault is stored in the control unit. The fault lamp for electric throttle control K132 does not come on. The engine runs at idling speed and does not respond to the accelerator pedal.

Emergency running program 2: If both accelerator position senders fail, driver input recognition is not possible:

• The engine only runs at idling speed.
• The fault lamp for electric throttle control K132 comes on.

Safety function: For safety reasons, the throttle valve is closed as far as a defined angular position when both the accelerator pedal and the brake pedal are depressed. If the brake is pressed first followed by the accelerator pedal, the driver input (torque request) is executed.

David Kavanagh <dak at rochester.rr.com> wrote:
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
>>>>>>> _______________________________________________
>>>>>>> Biturbos4 mailing list
>>>>>>> Biturbos4 at www.audifans.com
>>>>>>> http://www.audifans.com/mailman/listinfo/biturbos4
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