New Alternator but not charging battery (no voltage output to battery)

[coolum]

Hope someone can offer some assistance as its a bit strange.
Battery fully charged - RACQ tested Alternator - no output .
Went to mechanics they put in new alternator and thought it fixed
I drove it home and battery light came on
RACQ tested again and (new) alternator had no output but battery fully charged.
returned to mechanic workshop and they put new (second) alternator in but same thing (no output)
Dropped another new battery to eliminate as problem and same result.

What is in between the Alternator and the battery that regulates the power back to battery that could cause this issue?
.
Thanks in advance for anyone who can shed light on this problem

Its a D3 V8 petrol 4.4 not your usual D3 diesel.

Cheers Steve

[veebs]

I am of limited help I fear, however our D4 3.0L needed a complete ECU reset to get the alternator working correctly after replacement. I thought the D3 system was simpler, and so can't imagine this would be your issue, but offer it just in case it helps...

[coolum]

When you are clutching for straws every suggestion helps. So a big thanks for your help.

[BradC]

Fuse 20E in the engine bay box is the voltage sense for the alternator.
It has a PWM output from the ECM to the alternator (alternator command) and an PWM return from the Alternator to the ECM (current sense).

The 3 wire connector on the back of the alternator has all 3 signals (2xpwm and voltage sense).

From very vague memory it won't power up unless asked to do so. So it'll need at least a voltage sense and PWM from the ECM.

I have a TDV6, so the extent of my diagnostic input is the wiring diagram and cervix manuel.

[coolum]

Thanks this may well be the answer although the guys did have the manual out on the fuse page when I picked up the car the first time .. so thay may have checked this already.
But thanks very dmuch for your input I will let the the guys know.
Cheers
Steve

[Graeme]

If the 1st new alternator worked for a while then stopped working then the battery sense wire may now be shorting to ground if it was pinched in the change-over, in which case fuse 20E will keep blowing.

[coolum]

It's my understanding that it may never have worked as when i picked up the car to drive home the red battery warning light came on.
I would guess that the guyshust assumed that once new alternater Installed the job was done and I wouldn't blame them for that.
I will mention this to them as a possibility to check as we work through the list...
Many thanks Graeme you are always so helpful so appreciate your knowledgeable input.
Cheers
Steve

[101RRS]

I bought a new alternator in October last year and it was a dud - battery light on as well as every other light on the dash. Exchanged for a new one and dash lights all disappeared and every things works well.

So they can fail from new.

[coolum]

Thanks for your comment but they have tried a replacement alt and it was the same - no output.. then replaced the battery as well to confirm it was not that.

Hopefully we may find the answer with one of the comment to date.

Will give this info to the blokes and post any success or failures.

Cheers to all for your help so far.

[Gravy]

I am not familiar with your vehicle however I had charging issues with my 2014 TDV6. Eventually traced the problem to the Can Bus signal conductor connected to the positive battery terminal. For some unknown reason this conductor undergoes several wire gauge changes with the joints only crimped. After making the joins into heat shrunk soldered joints my charging issues were resolved.