General Alternator Lamp Flickering after Start

[umanemo]

I am asking this for a friend with a 2014 FIAT Ducato 3.0Lt

It seems that his alternator indicator lamp is flickering after ignition and when driving. He has found a reference somewhere online to faulty diodes in the warning circuit. I am not sure as my Ducato is Yr. 2000. An antique by ECU standards.

What he is asking is if these diodes exist outside of the ECU circuit board and if they are accessible to be replaced? Or... if there is another explanation for the dashboard lamp flickering?

Just for reference, he has confirmed with his mechanic that the alternator is healthy and delivering full charge current and voltage when running normally.

Maybe someone has a few thoughts on this anomaly. Thanks!

 

[jackwhoo]

Hi , the -ve battery lead/s are worth checking.
Good luck
Jack

 

[umanemo]

Thanks Jack, but he says, "Where is the -ve exciter connection?" I don't know his alternator config. so I cannot advise him.

 

[rayc]

Any help? The D+ Signal from the alternator operates the warning lamp via the body control module.

 

[jackwhoo]

Thanks Jack, but he says, "Where is the -ve exciter connection?" I don't know his alternator config. so I cannot advise him.

You are welcome, I was referring to the large -ve ground wire/s at the battery /engine/ body. If loose or degraded can cause all sorts of problems.

 

[umanemo]

You are welcome, I was referring to the large -ve ground wire/s at the battery /engine/ body. If loose or degraded can cause all sorts of problems.

I'll relay that and get back here with his answer.

 

[umanemo]

Any help? The D+ Signal from the alternator operates the warning lamp via the body control module.

I'll have him chase the D+ wire. Thanks for the schematics. That will be a great help when we chase this issue over the phone together.

 

[Anthony489]

Hi

Just to put you in the picture a bit more. The alternator has large built in rectifying diodes and a built-in voltage regulator. The main output (big terminal, thick wire) is stabilised at about 14.5 volts regardless of engine speed. Current flows to the battery and returns via the metal of the engine block and the alternator fixing bolts.

There is also another output from the alternator called D+ (smaller terminal, thinner wire). This is driven from its own set of diodes within the altenator body. the D+ output is sent to the body control module so that it "knows" when the engine is turning the alternator. The D+ output is also used on motorhomes by the management system for things like the leisure batteries and automaticallly retracting door steps when you start up. The D+ output is not meant to supply any appreciable current, it's just a control signal.


There may be a problem with these small diodes (not a DIY repair) but this is unlikely. There may also be a problem with the D+ wiring or connections e.g. corrosion, rubbing/shorting wires. So these are the things to check.

 

[umanemo]

Thx Tony, my friend is awaiting the weather in southern France to continue diagnosis. My suggestion at this stage concurs with your evaluation. His D+ must be loose or shorting somewhere. As soon as he replies I will return to this forum thread to let you know what he found.

Stay dry, stay healthy!

 

[Gengis24]

hi , Had the same problem, changed my earth strap(noted for that) now no lights