Possible alternator issue?

[SaulHeno]

Hey, B6 Passat 2.0TDi BKP here

No idea if this is normal behaviour so i thought i’d ask. I’ve noticed that my alternator does not charge the battery when the car is first started until i go over 2k RPM. After that it charges fine at any RPM including idle. Basically: Start Car -> Battery at 12.X volts @ idle -> tap throttle to over 2000 RPM -> battery 13.X @ idle. Is this normal behaviour? I’m used to my MX5 just kinda always being at 14v

It’s causing my LEDs in the front to flicker and throw errors on the dash. If i start the car and turn on my lights, flashing and errors. If i rev the car to 2k after starting, THEN put the lights on, nothing. Works fine for the most part

I also noticed a while ago the rear defroster light would blink over and over when i tried to defrost my windows over winter before work. I’m thinking it’s related? That the defroster was trying to run from the 12.X volt at first start idle?

My thinking is load management maybe? I have an intermittent 01117 code for DF signal implausible for the Alternator. I feel like my options are the wiring harness for the alternator, cleaning and checking the grounds, and then maybe the alternator itself?

Cheers, sorry for the long post

[VAG-Abound]

I have an intermittent 01117 code for DF signal implausible for the Alternator. I feel like my options are the wiring harness for the alternator, cleaning and checking the grounds, and then maybe the alternator itself?

We had that on our Touran. I found that the relevant wire running from alternator was being scuffed by the main fans at the front. It was visible when checking from below. I fixed the break and rerouted / secured the wire.

I also noticed a while ago the rear defroster light would blink over and over when i tried to defrost my windows over winter before work. I’m thinking it’s related? That the defroster was trying to run from the 12.X volt at first start idle?

Used to happen to us as well and indicates that the body control module knows that the battery is low, so won't let certain things run. As well as not turning that demister on I noticed that the electric windows wouldn't auto-roll - had to keep the button pressed.

No idea if this is normal behaviour so i thought i’d ask. I’ve noticed that my alternator does not charge the battery when the car is first started until i go over 2k RPM. After that it charges fine at any RPM including idle. Basically: Start Car -> Battery at 12.X volts @ idle -> tap throttle to over 2000 RPM -> battery 13.X @ idle. Is this normal behaviour? I’m used to my MX5 just kinda always being at 14v

It’s causing my LEDs in the front to flicker and throw errors on the dash. If i start the car and turn on my lights, flashing and errors. If i rev the car to 2k after starting, THEN put the lights on, nothing. Works fine for the most part

I never saw the 12V / 13V change, but we did have dimming segments in the display when starting the engine due to low charge. In the end the fix was discovering that the alarm siren was faulty due to water ingress and drawing current when the car was parked - but not making a noise because of the damage. Swapped that and all well afterwards on the low battery thing.

[SaulHeno]

Cheers for the great reply! I really appreciate it.

I’ve only ever seen one other post with this issue with charging, going from what they said (think it was on the Transporter forum) my leading theory is the DF wire on the alternator is broken or damaged, so the ECU isn’t calling for charge because it has no idea what the alternator is doing. Then once we go over 2K ROM the ECU goes “well we need something, turn on the alternator”. I’m just spitballing but it makes sense to me. I think.

I actually had an alarm issue recently funnily enough. I disconnected the convienience module and lost my alarm for about 2 weeks. It came back but no idea why. I had a few battery dead when i went to start before, and I did a parasitic draw test across the fuses and found the car goes to sleep properly so i have that going for me ��. I think it was just my OBDEleven accidentally keeping modules awake while the car was off.

I’ll inspect the alternator wiring and go from there. Thanks for the advice I really appreciate it!

[VAG-Abound]

I meant to include these:

53 plate Touran battery drain fixed - it was the alarm horn

Touran T1 P1503 Alternator Term. DF Implausible: Fan worn through loom

[Crasher]

That code has the same affect as in older cars where the alternator warning light didn’t work so the alternator doesn’t get its exciter power meaning it needs a good rev to kick in.

[mickeybo]

The regulated voltage should be between13.8 vs & 14.5 volts easly enough checked out by a very simple methoid