hieuln

Yes, as I said I always measure the voltage of the 2 jumpstart points under the hood and compare it with the hidden OBD values. Is that good enough or should I measure directly from the alternator output?

seanjordan20

No measure from the alternator. This way you have nothing in between the testing device and alternator. Then work your way to the battery. You should be able to isolate doing this method.

Redballs1

No matter where you check it from you can tell if it’s either charging or not charging. It’s obvious to the OP when he looks at the hidden menu that sometimes it is and sometimes it isnt you can still have a perfect alternator with zero output if the circuit to the battery is broken elswhere.

seanjordan20

When testing an alternator you don't start at cables going to the battery. If testing from the battery first you still have cables in between that can be bad or the alternator. This is why you test from front to back to isolate the problem. Troubleshooting 101. I'm not saying you can't test an alternator from anywhere along the line I'm saying to test it effectively you start at the alternator.

Redballs1

Well if you read the post it states that sometimes it is charging and sometimes its not, and i’m suggesting as you are that there may be a break in a cable as mine was and he should prove or disprove this possibility by making a parallel connection between the two connection points with a jumper cable, the alternator has had a new regulator and new bushes to no avail. I’d rather clip a jump lead on to check before fitting a new alternator.

seanjordan20

My sediments exactly. I don't assume the anyone knows what they are doing when troubleshooting. I try to tell them how to correctly troubleshoot so they know in the future proper procedure.

You can always get a bad part so I like to start from the obvious and work back. It should not be the alternator but you can't remove it from the table unless you test it correctly which is to test it at the mount point.

scottalexander

Do we know how old the battery is?

Is it possible a battery cell is bad and malfunctioning?

With all the IBS battery tinkering, are the battery cables at 5 nm of torque?

The voltage regulator was replaced. Is the B+ cable on the alternator tight enough?

Is it worth back probing the alternator wiring harness connection for damaged wires?

hieuln

I tried to check the cable today but unfortunately I can't check the under the car cable. I jack the car up but still can't see it (I have 4wd version). Maybe I have to drive to the garage to lift up the car and check it but with the current situation in Germany, I don't think that I can do that soon.

I also checked the cable runs from the positive battery terminal to under the boot floor, everything is good.

@scottalexander I have 2 battery with 2 years old and 9 months old with same problem. I replaced this battery 2 years ago when seeing the issue, then it happens again so I replace again 9 months ago. Of course after replacing the battery it was good for some months.

I also pay attention to the torque when closing the battery terminal and set to 5.5Nm when closing it.

When I replace the voltage regulator brushes 2 days ago, I examined the alternator and connections on it, there was no issue at all. One point I notice when replace it, the surface in contact with slip rings of the brushes is not even, somehow like the carbon is burned and melt down. Also the slip rings is not shiny, it's dark and dirty. So I cleaned it up by sanding paper. At least after replacing, when turn on the engine, the voltage show 14.0v so I assume everything works good. However, after driving for 10 mins, turn off and on again, the voltage decrease from 12.5v til 10v in about 2 - 3 minutes like I described and a hiccup it surges back to 14v.

In case of disconnected IBS, I would expect to have the voltage at always 14.4v, right?

I'll try to test the jumping cable maybe by tomorrow, it's not easy to reproduce anyway. But I have more time to stay at home and try to fix it right now, all because of corona

Redballs1

Within a few seconds off start up a healthy car will show 14v or more on the hidden menu, start your car and if its less than 14v put the jumper cables on from battery to jump start point while its running, iff the voltage jumps up to 14v or more then your cable is faulty

hieuln

Sorry for the late reply.
I only had time yesterday to try out the proof. So I did a lot of on and off to test the alternator. I hook up a multimeter to the B+ point under the hood to measure the voltage. Here is the results:
- 10 times the voltage rise up to 14v after some seconds
- 2 times the voltage didn't raises up after 1 - 2 minutes, so I connected the jump cable from the B+ under the hood to the B+ of the battery as suggested by @Redballs1 , after connecting, it rise to 14v
- 2 times even with the jump connection, the voltage didn't raise up after some minutes. However, wait a bit longer, when the voltage dropped to about 10 - 10.5v, it rise to 14v.

So, actually I don't know what could be the reason now. Any further suggestions for me?