2007 Volkswagen Passat Intermittent Charging Alternator

MITCHELL BACON

MEMBER
2007 VOLKSWAGEN PASSAT
4 CYL
2WD
AUTOMATIC
42,000 MILES

I have a 2007 VW Passat 2.0T with an alternator charging problem. It charges intermittently or not at all. It does not charge the battery fully. The alternator has been replace, however it did not fix the problem. Wiring harness has been check and was found to have good continuity. The mechanic suspects that either the Vehicle System Control Module or the Engine Control Module is faulty. I understand electronic very well; however without schematics for the two modules, I am not able to determine how the two Control units function with the alternator to properly charge the battery and supply vehicle operating power. From a high level wiring diagram we can see there are two wires that appear to be routed to the alternator field windings. Can you provide any suggestion of what could be the problem and/or an explanation of how the two unit work to maintain proper charging. B.T.W. The generator warning lamp has never turned on (even though the batter voltage has drop below 10 volts).

Thanks,

Mitch

1 Reply

MATHIASO

MECHANIC
1,209 POSTS

Hello Mitchell Bacon

Have the alternator been tested before it is replaced?
The generator lamp have never been turn on? If no, the problem may be some place else.
What about the battery drain, or a dead cell in that battery.
Does the charging problem occurs while driving? Or after the car park overnight?
When do you notice 10 volts drop for the battery?
Have the battery been load tested? Or replaced and then discharged again?

Thank you.