tps wiring/voltage check/descrepancy '91 200 20V tq
b.benz at charter.net
Thu Sep 11 13:57:54 EDT 2003
> From: benswann at comcast.net
> You may be correct that I am chasing trivia. Also, it is amazing what omitting
> a comma will do. Statement should have said:
> No, connector unplugged, not "no connector unplugged"
> That is, I tested with the connector unplugged from the TPS. Harness
> needs to be connected to ECU in order to supply voltage through Pin 1,
Yes, voltage across the pot is supplied from the ECU across pins 1 and 2,
off hand I don't know the polarity but it doesn't matter.
> From what I gather, 5V feeds via wire/pin 1 and returns to ECU via
> pin 3 (similarly with pin 2). Pin 1&2 register a full 5V. Pin 1&3 don't.
Pin 3 is an ECU input signal from the TP, not a supply voltage and therefore
should not be tested as such. Cross out that part of the Bently voltage
test. It is meaningless and therefore suggests a useless exercise.
> Continuity test shows wires for 1&3 when combined/looped back, round-circuit
> show almost 0 resistance. Probably should run separate wire to answer
> everyones scepticism about the wires, including my own. For the moment we are
> working on verifiable assumption.
IMO, the probability that you have a wiring harness problem is nill.
> I must conclude at this time that 1) wires are good, although no harm in
> checking. 2) either ECU is bad (internal problem) or Bentley spec. is off.
> far 3 out of 3 cars that I have information on have this problem, which is why
> I am wondering if Bentley gives the fully correct procedure.
> I don't have the special VAG harnesses used, but beleive I have been deducing
> the correct wires to analyze. I am pretty sure I have been doing my test
> properly. Most of what I have been replying back on is that folks did not
> my original email throroughly and later answers back to well meaning replies
> result in further confusion such as yours. Anyway, assume I have been
> following the procedure per. Bentley. and assume wiring is good. What then
> does the low voltage mean?
It is not a low voltage! (or only re: the Bentley error.) You are reading a
leakage voltage from a high impedence input circuit that is meaningless for
> What does your voltage between pins 1&3 read?
I won't waist time measuring it.
> Maybe this is trivia, but I have not found/fixed the problem yet. I am sure
> there is a problem and I will get to the bottom of it eventually.
Keep an open mind! Apparently the only reason you have to suspect a TP
problem is the erroneus Bentley voltage test. Move on, if the TP resistance
values are OK.
> Yes to some
> degree DFI-IAB and leave well-enough alone, but when a second and/or third
> component malfunctions later on, troubleshooting gets compounded.
In this case, maybe your rational is the initial compounding factor.
>> IMO, you are persistant in your persuit of trivia.
>>> From: benswann at comcast.net
>>> No connector unplugged - as per Bentley.
>> Not per Bentley, if you are following inst. on pg 24-130-1 for the
>> measurement of V between #1 and #3. The connector is to be unplugged from
>> the TP for this as well as the supply voltage (#1 and #2) measurement. I
>> have not measured mine, but this (#3) is an ECU input signal, and therefore
>> is a trivial (high impedence) measaurement without the TP connected. Assume
>> Bentley is wrong again in this instance.
>> Of greater import are the TP resistance measurements. If you refer to the
>> schematic, pg 542, you see that the TP has a fixed resistor on either side
>> of the tapped pot resistor, so the operating voltage at #3 can never be as
>> large as is the V on #2, relative to the supply, #1. If your R values check
>> out and the pot gives a smooth change in R, don't sweat it, look elsewhere
>> for your problem.
>>>> Did you have the connector plugged in when checking the voltage?
>>>> Commonly there is a series resistor on the 5v line to protect the ECU.
>>>> I'll almost bet that you're supposed to unplug the TPS when checking
>>>> this voltage.
>>>> On Wednesday, September 10, 2003, at 02:41 PM, benswann at comcast.net
>>>>> Thanks a lot for checking. It seems like there is quite some
>>>>> variation in the
>>>>> readings. Anyone else checked theirs. Two cars I've checked have
>>>>> around 3.5V.
>>>>> Bently says voltage between pins 1 and 3 on TPS connector should be
>>>>> 5V. If not
>>>>> then bad wiring or ECU. Assuming I have correctly checked my wiring,
>>>>> then what
>>>>> causes this variation.
>>>>> Note: Wiring diagram indictes a straight thru connection between TPS
>>>>> and ECU
>>>>> on Pin 3m, so really not much else there to test.
>>>>> [From: "motogo1" <motogo1 at cox.net>
>>>>> To: "Audi 200" <200q20v at audifans.com>
>>>>> Subject: Re: Throttle position sensor/circuitry checking w/resp. to
>>>>> poor fuel
>>>>> Date: Tue, 9 Sep 2003 23:19:47 -0700
>>>>> Well, on my TPS, voltage between pins 1 and 2 is 5V..in spec per
>>>>> Between pins 1 and 3, 1.6 volts. Not even close to Bentley spec. My
>>>>> car is
>>>>> chipped with IA III+ and runs strong, with no problems. I'm going to
>>>>> have to
>>>>> check the mileage, to see what I'm getting.
>>>>> Gary Martin
>>>>> 94 UrS4
>>>>> 91 200 TQA]
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>>> 200q20v at audifans.com
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