Smart 450 sometimes not charging

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Joined: Sun Jul 06, 2014 2:40 pm

Smart 450 sometimes not charging

Post by terbo » Tue May 23, 2017 11:39 am


Friend of mine has a (Mercedes) Smart 450 that sometimes doesn´t charge.
His Garage put in a new alternator, but same thing happens.
The alternator has a Big Wire to Battery and one to ground, and one small
one called PH-IN coming from the Engine ECU - Pin 47.

I yesterday took a peak at this wire, it has connection, without problems,
we even connected a sperate wire just in case, but thats not the Problem.

I made two caputures, one with it charging, one with not charging.

If i look at the two you can clearly see, where the ECU changes the PWM Signal to
the Alternator and then it charges.In the shot with no charging, the PWM does not change.
But i noticed as well, that when its not charging it has this strange "hash" on the
tops off every Signal, and the whole trace looks "fussy", but the Probe Places didn´t

Sometimes it charges after startm then you can drive 5 Miles, sometimes 50,
then it just stops charging while driving, sometimes it was charging till shut off,
you come back after shopping and it doesn´t charge after startup or after standing
one night.

As the Alternator is new, i would think the Engine ECU is going bananas,
or does someone have a better idea ? Or have this problem before ?

Thank Chris
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