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FIXITMAN
FIXITMAN, Master Technician
Category: Audi
Satisfied Customers: 17142
Experience:  ASE MASTER CERTIFICATION, AA DEGREE AUTOMOTIVE/DIESEL
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I can't figure out my alternator not charging. I already

Customer Question

I can't figure out my alternator not charging. I already took and out and test both the battery and alternator and they are both good.
Submitted: 1 year ago.
Category: Audi
Customer: replied 1 year ago.
I have a 2010 Audi A4
Customer: replied 1 year ago.
Already checked all fuses. None are blown
Expert:  FIXITMAN replied 1 year ago.

Hello, my name is Bobby. Thank you for the question. Typically this occurs because of a failure within the positive battery cable. The issue is typically in the section of the wire that connects to the large post on the alternator. This wire develops high resistance and this occurs. I would either do a resistance test of this or if you have a voltage meter you can check the end at the alternator and the end at the starter and see if the voltage drops off. If the voltage is higher at the alternator than at the battery then the wire is bad. If not then you are not getting an on signal from the PCM which may be failing.

Customer: replied 1 year ago.
I checked the on the dc 20v on the multimeter. the wires from the alternator voltage was not higher than the battery voltage. Pcm failure where should that be? I've also checked the ground cables that were visible and didn't see any issues either
Expert:  FIXITMAN replied 1 year ago.

What is the output voltage of the alternator?

Customer: replied 1 year ago.
from the vcds reading it says 11.60. When the car isn't on. Just on ignition. When I turn the car on the battery goes from 12.04 to 11.7-8.
Customer: replied 1 year ago.
I've put a new alternator on and retested both the new alternator at a specialty shop. They said both alternators are working. The battery was recharged and cells checked. The battery is still good.
Expert:  FIXITMAN replied 1 year ago.

Does the violet/blue wire have battery voltage when the key is turned on?

Customer: replied 1 year ago.
I don't remember. On that wire. I also started the car with both alternator wires removed. The idiot light did not come on.
Expert:  FIXITMAN replied 1 year ago.

If the battery is not charging and there is no light then your battery module, located on the battery may be failing. The system will also only charge when it thinks it needs it. You need to see if this wire has voltage. If it does not then the monitor may have failed.

Customer: replied 1 year ago.
Ok can you walk me through that?
Customer: replied 1 year ago.
I get confused sometimes with the wiring because I routes all the way to the trunk.
Expert:  FIXITMAN replied 1 year ago.

I would need to know what the voltage is at that wire at the alternator. I would then need to know what the voltage is at that same wire at the little box on the battery. Also see what the large red wire at that box reads.

Customer: replied 1 year ago.
Ok. I can't access the wire right now. Can I come back to you on that information? Also are you referring to the little box that is connected to the negative terminal? And what do you want me to read with the mulitmeter? Ohms or dc 20v?
Expert:  FIXITMAN replied 1 year ago.

Yes, you can come back anytime with that information. Yes, that is the box I am talking about. Do the test on the 20V DC scale.

Customer: replied 1 year ago.
Battery is low (I know)11.7 battery -with ignition switch on -
8.96-9.20 jumps up and down violet wire on alternator with ignition switch on11.63 on wire connecting to black thing and all read wires read the same. Same readings with ignition on and trunk light on. Readings go up to about 11.8 when ignition is off.
Going to charge battery
Expert:  FIXITMAN replied 1 year ago.

What size battery is in the car?

Customer: replied 1 year ago.
It's oem. I don't know the actual size. I had to take it Audi to get it fixed. They found a short in the alternator and starter harness. It's getting replaced right now. With labor cost and everything...it was 900...
Expert:  FIXITMAN replied 12 months ago.

Ouch. I thought it was in the harness but from the tests you did and the results you gave me it sounded like it was ok. Hopefully it will be worry free after this.

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