Red battery light came on and the charge voltage was barely reaching 11.0 Volts. First replaced the battery, but that didn't solve the issue. Then replaced the alternator.

OEM alternator: 180 Amp Valeo; 7 groove pulley; Part No. A 642 154 04 02
Replacement alternator: 220 Amp; 8 groove pulley; No-name brand on eBay for $193.00 including tax; Looks identical to Bosch 220 Amp that is also OEM on the W164

I bought this new alternator on eBay. I was a little sceptical about it before it arrived. Having received and examined it, I'm very impressed with its apparent quality. It looks exactly like the 220 Amp Bosch alternator which is also an OEM alternator on the W164. I've had this new alternator installed in my vehicle for a week now and it works perfectly.

To replace the alternator:

1. The battery is located beneath the front passenger seat (on the right). Move the seat as far forwards and upwards as possible to access the battery below more easily.
2. Disconnect the lead from the negative battery terminal.
3. Slacken the serpentine belt and move the belt off of the alternator pulley.
4. The old alternator was removed from the top, but the bottom 2 holding-down bolts on the alternator, and the plastic electrical connection were removed from underneath the vehicle. For that, remove the plastic covers on the underside of the engine bay.
5. From the top and above the alternator, remove the air duct to the RH air filter housing, remove the RH air filter housing (not absolutely required, but makes things easier); disconnect the joint on the air duct between the intercooler and the intake manifold; disconnect the electrical connector from the auxiliary water pump(?) and remove its holding-down bolt on the chassis - no need to take any water hoses off, simply move the line out of the way. This provides the room required for the alternator to come out through the top.
6. Pull the black plastic cap straight off the red positive lead connector on the alternator. Disconnect the red positive and the earth leads from the alternator.
7. Hold the alternator and remove the last holding-down bolt.
8. The alternator is now free and can be brought out through the space created in step 5.
9. Installation is the reverse of the removal. On the new alternator, use the 7 grooves closest to the alternator body.





[img alt="(1) Alternator
(2) Belt Tensioner"]https://cimg3.ibsrv.net/gimg/www.mbworld.org-vbulletin/731x688/01_16_09_18_b_serpentine_belt_layout_c0ad27a00db18 f5a718475f69a02a0cc7f08b1e4.png[/img]
(1) Alternator (2) Belt Tensioner

Turn anticlockwise on belt tensioner to release tension in serpentine belt; 17 mm socket

Front view of alternator before removal; 7 groove serpentine belt

View of alternator as seen from below; Two holding-down bolts accessible from here

Disconnect plastic electrical connector from alternator

View of inside of electrical connector

View of alternator from the top; Disconnect lines to be moved to the side to make room for the alternator to pass through

Loosen inline water pump from chassis in order to move out of the way

RH air filter box removed to improve access to alternator

Remove main power lead from alternator; Top holding-down bolts

Remove main power lead from alternator

Alternator coming out through the open space created in previous steps

New 220 Amp Bosch-look-alike alternator on the left; OEM Valeo 180 Amp alternator on the right

The new alternator comes with an 8 groove pulley; The original alternator comes with a 7 groove pulley; On the new alternator, use the 7 grooves closest to the alternator body for perfect belt alignment

New alternator on the right; Old alternator on the left; The electrical connectors are in different locations on the new alternator, but they work perfectly

New alternator almost in position

New alternator bought on eBay

 

Nice write up!

 

Thank you. When setting out to do this, I couldn't tell whether the alternator should come out through the top or through bottom. I had seen a write-up somewhere that the alternator is removed through the bottom, but on closer inspection that to me seemed either improbable or needing to remove some major components in the space below the the alternator. Yes, some work needs to be done from underneath the vehicle and some from above, but in the end, the alternator can come out through the top without requiring much dismantling of other components above the alternator. The Bosch alternator is very slightly larger than the Valeo, but both the Bosch and the Valeo alternators fit through the opening above. It does take some wiggling though!

 

Additional photos:


7 rib serpentine belt on new 8 groove pulley

Photo showing items that obstruct removal of the alternator through the top of the engine bay. The electrical harness can easily be pushed aside - it does not require to be disconnected.