on the growing sophistication of cars....

Huw Powell audi at humanspeakers.com
Tue Mar 10 13:18:06 PDT 2015

There's actually a corollary to this in auto wiring diagnostics - 
checking for 12v power to ground with a voltmeter won't tell the whole 
story because of the very high impedance/miniscule current draw of the 

Testing with a test light or a spare parking light bulb will not only 
verify the presence of power, but the ability to deliver some current 
through the connections, wiring, and any grounds involved.

- Huw

On 3/8/2015 5:35 PM, Dave wrote:
> to close this out.  i checked a bunch of batteries directly using a voltmeter and they all registered over 3 volts.  using the 100ohm resistor across the the cell yielded markedly different results, in some cases barely about half (around 2 volts).
> the end result was 6 batteries thrown out.
> +1 for this method. i wish i'd known about it before.
> dave
> '08 rs6 avant
> '12 vw passat alltrak
>> On 25/02/2015, at 6:25 pm, PSD <psdooley at verizon.net> wrote:
>> Thank you for sharing that.
>> A note on those little button cells- test for voltage with a resistor across
>> the DVM leads, like 100-200 ohms.  If not, they can show much higher voltage
>> than what they actually have, kind of like a surface charge.
>> http://www.candlepowerforums.com/vb/showthread.php?311628-What-CR2032-open-c
>> ircuit-voltage-is-considered-quot-dead-quot
>> -----Original Message-----
>> From: quattro [mailto:quattro-bounces at audifans.com] On Behalf Of Dave Eaton
>> Sent: Tuesday, February 24, 2015 3:44 PM
>> To: quattro at audifans.com
>> Subject: on the growing sophistication of cars....
>> my wagon has ³advanced key² which means that it provides keyless entry.
>> which can be surprisingly handy.  so last month, after a long holiday away
>> the keyless bit wasn¹t working.  so i swapped the battery out of the remote
>> with a new battery.  still no joy.  use my other keys and get intermittent
>> results.  replace the battery in the other unit.  still intermittent at
>> best.  sometimes even the remote locking/unlocking functions would not work
>> until i had pressed the remote 6-7 times.
>> if i take it to the dealer, i them become a hostage to their diagnosis, and
>> this is stuff i should be able to figure out myself.  sigh.
>> i access vag-com.  i am seeing multiple 955/966 errors but they are recorded
>> as intermittent.
>> access elsawin.  try to understand the interface of advanced key with normal
>> remote lock/unlock as the failure mode is influencing both. there are 3
>> aerials one in each rear door and one in the trunk.  there is a reader unit
>> under the dash and a precessing unit under the centre console.  to get
>> access to all that gubbins would not be the work of a moment.  check out the
>> wiring diagrams, there is a common ground or 2 but nothing obvious that
>> would contribute to the failure mode that i am seeing short of a fundamental
>> system failure.  there is some talk on the internet of how a faulty door
>> aerial could cause the others to stop working.  could be door wiring.  the
>> failure occurs irrespective of which side of the car i am accessing.
>> mentally prepare myself for $500 labour and $500 parts bill from the dealer.
>> with vag-com i run control element diagnostics on the start module and note
>> that all tests pass with not faults logged.
>> i finally follow a hunch and and replace both remote batteries again with
>> new ones from the supermarket.
>> it all works like a charm.  $6.
>> and a bad batch of cr2032 batteries that is now in the trash.
>> dave
>> ¹08 rs6 avant
>> ¹12 vw passat alltrak
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