[V6-12v] Low voltmeter readings
urq222 at ymail.com
Mon Jun 15 09:22:56 PDT 2009
.... is this a bona fide change in behavior? Do you have a recollection that the voltmeter did not do this before? You say the reading appears correct when the fan is not running, that would tend to indicate that the alternator is OK.
On many of the older Audis the ground reference for the voltmeter came from the circuit that also supported the blower for interior heating/cooling ... turning on the fan would cause the voltage measurement to drop due to the blower current in the ground causing a voltage drop in the ground line itself. Those cars had a manual blower switch and you could watch the voltage measurement change as the blower was set to various speeds. This could also affect other gauges on the console ... in fact I just observed this today driving the urq ... the coolant temp was pegged with the blower on high ...
Put a voltmeter on the battery terminals and see if they show similar symptoms. If you can see the voltage drop at the battery, it may be that the grounding wire from the block to the frame of the car is loose or breaking, making it so that the alternator cannot supply full rated current to recharge the battery. It may also be that the battery is on its way out (as was suggested in another response).
Low readings when the cooling fans come on (less than 12v). Drops from
where it should be though no measurements taken.
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