Charging system nightmare - DFM alternator
Posted to Technical Discussion Forum on 1/16/2014
7 Replies
It is a very weird problem. At least to me.
This 2008 TFSI Passat has the charging lamp ON. Every time
engine is turned on alternator will not charge. But, after
accelerating engine to about 1800 / 2000 rpm it starts to
charge normally and continuously. Even at idle speed. But
charging lamp (red battery symbol) will never not go OFF.
There is no codes on ECM memory.
I used a known good alternator on car and problem continues
exactly the same. Assembled car alternator on other Passat
and alternator/regulator are working normally.
My doubt about DFM alternators equipped cars:
-The signal DFM to ECM has something to charging control or
is just used by PCM to measure alternator load in order to
control idle, engine load???
-What problem would prevent alternator to charge after
engine start, while in idle. And why it starts charging
after accelerating engine to 1800 rpm?
- In the case of the Passat what kind of information is used
to turn the charging lamp OFF? In other works: what control
module will ask instrument panel to turn charging lamp OFF?
ECM, J519 power supply unit???
I made a Erwin subscription but found no explanation about
the DFM + L alternator charging system logic.
Thanks
Mauro Brisola Owner/Engineer Multi Marcas Curitiba, Brazil
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