Charging Question

[JonLeeper]

Not my VW but a quick question:

Wife’s daily driver (Peugeot 406 Est diesel) came up with a "Battery Charging Fault" yesterday and refused to turn on the rear window demist. After a while it stopped and all was well.  This morning the same message and the car refused to run the fans, front demist, rear demist and was, apparently, hunting or struggling for power on the school run this morning. 

Before she left I put the multi-meter across the battery and it was fully charged at a constant 12.46v, and that was after starting the car twice and stopping it immediately.  So I think that the battery is ok.  When the car was running the power across the battery dropped to a steady 12.18v but no change even when revved.  As far as I am aware the alternator should charge at about 15v without any other systems (lights, A/C, radio, etc) so this would indicate that the problem lies with the charging system.  The alternator belt appears to be fine and tight, it is hidden really well and difficult to reach (god knows how difficult it will be to change) but you can just reach the belt to test tension, so I am assuming that it is an alternator problem and the fix will be a new alternator.

Am I flawed in my logic or have I missed anything?  All responses welcomed as I have to fix it for her before tomorrow as she has a MRI appointment and the kids school run etc.

Jon

[madgti]

i'm sure the battery should be putting out 14+ volts fella i'd try that first

[JonLeeper]

i'm sure the battery should be putting out 14+ volts fella i'd try that first

Not sure where i said that!  The battery is steady at 12.46v with the engine off and constant at 12.18v with the engine running.  I think that the alternator should be pushing out about 14v to charge it and run the car's systems.  I think that the complex management guff fitted to modern(ish) cars mean that if it dosent see that voltage it prevents you from draining the battery by stopping the sub-systems from working, such as the rear window de-mist. 

[rubjonny]

battery will be about 12v engine off, and over at least 13v when running. i recon you might have a problem with the equivalent wire to the blue wire found on VWs, that runs to the battery warning light in the dash. start at the alternator and look for any thin wires, follow these as far as you can checking for damage or disconnected plugs.  if it all looks good take the bush pack off the back, on most VWs its held on with 2 screws, on this car it might be under a plastic end cap?

once off, clean up the metal ring(s) around the attachment screw holes, and if you look at the hole it came out of you should see some kind of metal prong that contacts the brush pack, clean this up and the contact face on the brush pack and put it all back together.

edit: being a diesel it may have 2 wires to the alternator, one for the rev counter and the other for the warning light. The warning light wire will be labelled D+