I've had some alternator woes over the past week.

Citroen Relay model II 2005 - 2.2hdi.

My alternator wasn't putting out anything:

  • Battery was down to 11.5v
  • Checked the alternator with a multimeter (same voltage as battery when engine on)
  • No bad sounds from the aux belt and belt feels newish and tight
  • No real trouble starting or turning over (despite the low voltage battery)

The old alternator was only about 10000 miles old. I figured the alternator's voltage reg had blown, instead of just replacing the reg I just got a whole new alternator (no time etc..).

I installed the new alternator with 3 of the bolts loosely on (not torqued all the way), and turned on the engine. It started putting out 13.5v, not perfect, but that's a lot better than what I had before.
So next I finish the mounting and install all the bolts properly. It starts only putting out 12.5v.

  • The old battery was dead, so I installed a new battery.
  • I checked the D+ battery light cable with a multimeter, it's putting out about 11.5v when ignition is on, I make sure it's clean and seated properly.
  • Re-checked all the alternator cabling, no voltage drop issues I could see.
  • re-seated the aux belt, make sure it's tightening properly when running. (listening to the alternator maybe it makes a light kind of "Geary" sound when running, but only when I go right up close.) No wobbling, no squealing, again belt seems tight and newish.
  • Remove any other components that might be parasitically draining the battery

Still only putting out 12.5v.

Then as a last resort I try slackening the bolts right loose again on the alternator

Suddenly putting out over 13v again (range 13.2 to 13.5).

My hunch is that the tensioner isn't doing its job properly, and that slackening the bolts puts a tighter angle on the belt so it starts driving the alternator properly. This would also explain the range and the fact that it doesn't seem to be full voltage (14v)

I feel like I've eliminated every other possibility, apart from maybe the bad luck of getting another duff alternator?

Is there anything else it could be, or I should try? It's a strange one because the belt seems almost new.

I've taken a video of the belt and will post a link later.


  • Welcome to Motor Vehicle Maintenance & Repair! Commented Apr 16, 2023 at 11:18


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