Tech Article: Audi C5 A6 Quattro 4.2 V8 Alternator

The C5 Audi A6 Quattro 4.2 V8 models as well as the S6 all used the same type of 150A alternator, Bosch type AL0797X, Bosch part number 0123520021. Audi has two part numbers for the same essential alternator. The old number is 038903018D. It was superseded by 077903015L.

If you’re not here for the technical analysis but would rather buy a used unit from us, then please select one of the links below. If we’re out of stock on one, choose the other; they’re essentially the same part except for the part number.

To remove the alternator, the serpentine belt has to be freed from the pulley, and then there’s a small bolt at the bottom and a 110mm-long Allen head bolt at the top. The back has three electrical wires. The thick positive wire is attached to the alternator using a 13mm nut. A smaller wire is attached to the alternator using an 8mm nut. Another small wire is attached to the alternator using a spade connector.

When shopping around, it’s a good idea to factor in whether or not the unit you’re considering comes with a front pulley; all of ours do but I noticed that our competition doesn’t always include it.

Another factor is the core charge. Some vendors charge it; we do not.

We also make a point of taking our alternators to the friendly local auto parts store to have them formally tested before we sell them, which is why we’re so comfortable offering a money-back guarantee. When buying a used alternator, including ours, it’s prudent to take that to your friendly local auto parts store for testing, before you install it into your vehicle. That prevents wasted time, and it rules out problems caused by the vehicle.

It might be tempting to consider a knock-off, but we prefer Bosch units, even if used.

It might also be tempting to consider an alternator from a non-V8 model, but they’re not interchangeable.


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