failing alternator? maybe pulley or connections?

[Spacecadet_CC]

In the last week I'm getting the "Alternator Fault: Battery Not Charging" warning, but it is coming on intermittently. After start it comes on after a minute or so, but sometimes will disappear 3 or 4 minutes later, maybe reappearing 5-6 minutes after that. Or not. I had one drive where it was on for nearly a half hour. And the next drive it did not appear at all. (turned off all electrical I could when it came on)

Multimetered the battery and it is holding charge on it's own. Multimetered the battery when the warning light was off and it was in the 14.6V range as you want. Multimtered the battery when warning light was on after about 10 minutes and it was down to 11.5V and ticking down. So it seems that the alternator is definitely failing, but not 100%. I'm charging the battery back up when not in use.

This weekend I'll pull the clip off and test the connections at the back of the alternator, do a multimeter voltage drop test, and will pull the belts and see if there is any play in the pulley.

Any other suggestions? Will an alternator fail like this or does it just go down 100% and never comes back to life?

6 months ago I replaced the water pump and thermostat along with the belts, but not the tensioner. (170,000 km on the odometer)
Thanks, all.

[SwankPeRFection]

Might want to check your crank pulley if you’re on the stock one? You might have an extremely lucky time bomb on your hands where it hasn’t decided to shred everything around it when it goes. Take a look at it while it’s idling and also when starting. If you see any minor wobble of the larger section don't run the engine anymore until you can replace it. If that’s fine, it could be the voltage regulator on the alternator or the alternator as a whole.

[Smac770]

"it was in the 14.6V range as you want", no you want it to be whatever the J533 is commanding it to be. You cannot sufficiently assess the charging system if you do not have a scan tool like VCDS that allows you to confirm the generator voltage being commanded (block 014) and battery voltage being measured (block 018). The voltage regulator on the alternator is LIN bus managed, not dumb managed. Block 015 will say if the fault is mechanical or electrical. I assume the mechanical fault will come up if the VR is reporting an insufficient input rpm. But I don't know that the generator rpm is a value you can see in the blocks; maybe something you could pull off the LIN comms if you had a LIN protocol analyzer.

So might be an electrical side issue of a flaky VR, or a mechanical side issue with flaky rotational input. As swank points out, the alternator pulley, which is an OAD, should be checked for play. That's what failed on my alternator, not the alternator or VR itself. The bad part is those things are half the price of a whole alternator.

[jordancl]

Also make sure that your battery connections are solid. One of my battery connectors was loose and would have an intermittent connection with similar issues, although it sounds like you've had eyes on your connections already so might be a non-issue.

[TC_S4]

In the last week I'm getting the "Alternator Fault: Battery Not Charging" warning, but it is coming on intermittently. After start it comes on after a minute or so, but sometimes will disappear 3 or 4 minutes later, maybe reappearing 5-6 minutes after that. Or not. I had one drive where it was on for nearly a half hour. And the next drive it did not appear at all. (turned off all electrical I could when it came on)

Multimetered the battery and it is holding charge on it's own. Multimetered the battery when the warning light was off and it was in the 14.6V range as you want. Multimtered the battery when warning light was on after about 10 minutes and it was down to 11.5V and ticking down. So it seems that the alternator is definitely failing, but not 100%. I'm charging the battery back up when not in use.

This weekend I'll pull the clip off and test the connections at the back of the alternator, do a multimeter voltage drop test, and will pull the belts and see if there is any play in the pulley.

Any other suggestions? Will an alternator fail like this or does it just go down 100% and never comes back to life?

6 months ago I replaced the water pump and thermostat along with the belts, but not the tensioner. (170,000 km on the odometer)
Thanks, all.

Your alternator regulator is failing, if you have vcds or Carista, you can monitor the alternator charging Watt. A good alternator charging between 300-600 watt, when it fails, it can go all over the place, like 100 watt or even 15000 watt.