W164 alternator change but battery light still on

[Mark A]

Broke down at the Glenshee ski centre a few weeks ago when the battery ran out of juice as the alternator wasn’t charging (engine turned off at about 9.5V). After being recovered home I put the battery on charge and then drove it to my local garage to change the alternator for me.

They have now changed the alternator and we are getting a good charging voltage +/-14V but the red light is still on the dash.

If I stick the battery on charge for a bit will the light go out again or does this suggest that there might also be a problem with the battery now.

 

[Tony Dyson]

I believe the new alternator needs coding to the car with Star, was this done by your mechanic?

 

[Mark A]

Nope, however when I had one changed on my previous ML they didn’t need to code it.

 

[mioba]

Was it a genuine alty.
Was it a MB Indy or a n other garage.

 

[Mark A]

It was an aftermarket alternator and not an MB indie as my nearest is 42 miles away (local garage is Renault main dealer).

 

[mioba]

Maybe ask them to delete the error (DTC). Some faults only disaaperar after the offending part is replaced and the error is cleared.

 

[LostKiwi]

Charge the battery overnight.
Disconnect and leave an hour.
Measure the voltage across the battery.

If it's under 12.4v your battery is had it.

 

[Taffy7hfa]

Sometimes a failing alternator will kill off the battery as well, they don't like being completly flattened.

 

[Richard Moakes]

Could also be the small auxiliary battery hidden behind the main battery, used for the Direct Select Module

 

[Mark A]

When I did finally got the car back from the garage it was the white battery light not the red one. I have changed both the aux and main battery (both over 5YO) but still have the light. STAR says the consumer battery is either missing or malfunctioning.

does anyone have a circuit diagram for the Aux battery circuit?

any fuses associated with the aux battery?

 

[Richard Moakes]

Fuse box info here https://1drv.ms/b/s!AhgVSHGRT5CR-khVEbU6zCUs072o