Audi Q7: High Voltage - Board/Generator Issues?

Hello everyone,

habe derzeit ein Problem in meinem Audi Q7 aus 2009 mit 3,0 TDI Maschine. Problem history:

"Dead battery -> Cause: Defective MOST controller in the Bose amplifier, resulting in increased quiescent current. The bus does not go to sleep, and after a few hours, the battery is completely drained."

Replaced the battery with a new one -> Swapped out the original 92Ah AGM battery for a 110Ah Varta Silver Dynamic wet cell battery. My old battery was almost 10 years old.

"The MOST controller in the Bose amplifier was replaced, and as a result, the entire MMI system worked properly for about 2 hours. Then, the amplifier failed again."

Now, to my actual question: Could it be that the voltage level in the vehicle is simply too high, and that this caused my amplifier to fail again? According to VCDS, the alternator is producing 15V, and at terminal 15, there are 14.7V with no consumers turned on.

Can the voltage regulator or generator be tested using VCDS?

I've attached a Screenshot of the voltage readings from VCDS. I would be very grateful for any information you can provide.

Best regards,

Hi there.

In principle, you should adjust the charging strategy/charging cutoff voltage when switching from AGM to a wet cell battery, as AGM batteries have a slightly higher charging voltage.
You would need to check in VCDS to find out exactly where that is located.

The displayed values are consistent with an AGM battery strategy, but this is not suitable for a new flooded battery because the voltages are too high. The charging voltage should be between 13.8V and a maximum of 14.4V.

However, this is not related to your problem, as the MOST amplifier should not be damaged by voltage surges that are considered moderate in automotive terms.

Hello everyone,

I wanted to share some important information here. According to an Audi data sheet for the Q7 4L with an AGM battery, the following specification is given regarding the permissible generator voltage:

Nominal voltage:
The generator's voltage regulator must provide at least 14.3 volts.

Undervoltage.
The generator voltage should not be below 13 volts. A voltage of 13 volts is still acceptable at low engine speeds and with consumers connected.

Overvoltage.
The generator voltage must not exceed 15.5 volts at high speed and with few connected loads.