Alternator
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Description – W220 Generator / Alternator / Charging System
Types – W220 Generator / Alternator / Charging System
W220 are equipped with two types of alternators. One with and one without coolant cooling.
Specification – W220 Generator / Alternator / Charging System
- S350, S430, S500: 14V/150A
- S55: 14V/180A
- S600: 14V/220A
Issues – W220 Generator / Alternator / Charging System
An alternator can fail or perform poorly due to:
- Bearings worn or noisy
- Voltage regulator electronic component failure
- Brushes worn
- Cable fracture
- Full wave bridge diode open or short circuit
- Stator winding open or short circuit
- Rotor winding open or short circuit
- Serpentine belt issues
Symptoms – W220 Generator / Alternator / Charging System
A faulty alternator should be recognised by the OBD vehicle checks and will display a dashboard warning message.
BATTERY CHARGE VISIT WORKSHOP!
Typical symptoms are:
- Charging voltage across battery terminal with engine running below about 13.8V.
- Alternator output voltage greater than about 15V. A good fully charged battery should be about 14.2V across the battery terminals.
- Illumination change in instrument cluster is usually an early indicator of pending alternator failure.
- A sudden sound of the alternator (high frequency whine) disappearance.
- Clicking sounds from the doors caused by car unlocking itself for safety purposes.
Solutions – W220 Generator / Alternator / Charging System
The W220 has very good in-built electronic checking systems and so you should be alerted to the usual failure mechanisms by the car itself. However with some electronic capability and the right tools it is easy to DIY diagnose most alternator electrical issues. Mechanical problems are usually diagnosed by hearing unusual sounds from the alternator.
Checking Alternator Voltage – In-built Test
Note: This method is not suitable for testing battery voltage, since several consumers activated will cause a non-objective measurement. Battery voltage must be measured without active consumers (ie with minimal load) and preferentially only across the battery terminals.
In-built Test
1. Insert key into the starter switch and turn to position 1.
2. Use steering wheel buttons to navigate to screen which shows the vehicle odometer.
3. Press R button on instrument cluster three times. The voltage reading should be displayed.
4. Start the vehicle. After few seconds the voltage display will disappear. However, you can locate it again using steering wheel buttons. The voltage reading with the vehicle running should be displayed.
Test Results - In-built Test
- Correct voltage measurement on non-running W220 ( with vehicle stationary for an hour or so with minimal load on battery) should be greater than 12.2V.
- Correct voltage measurement on running W220 should be around 14V.
Checking Alternator Voltage – DVM Method
Use an accurate Digital Volt Meter (DVM) and monitor the alternator output at the large terminal directly on the alternator.
Test Results - DVM Method
Correct voltage measurement on running W220 should be around 14V.
Parts Required - DVM Method
- Digital Volt Meter accurate to at least one decimal place.
Tips - Replacing Alternator / Regulator
- Be sure to use the proper tools throughout the process and support your ratchet while loosening the bolts that secure the alternator. Otherwise you run a (small) risk of breaking the tab off of the timing case cover.
- After performing this DIY the Pre-safe error comes up because the windows are not synced. When the Pre-safe activates in a crash condition, the sunroof will close, the doors will unlock, the rear door child safety locks will disengage and all the windows will close. If the windows are not normallised / reset / synced, Pre-Safe will deactivate and light up the Instrument Cluster.
DIY Method - Replacing Alternator / Regulator
Link is to an excellent detailed article for a DIY Alternator / Regulator replace.
http://www.benzworld.org/forums/w220-s-class/1688209-alternator-voltage-regulator-replace-diy.html
DIY Method - Replacing Alternator Bearings
Link is to an excellent detailed article for a DIY Alternator Bearings replace.
http://www.benzworld.org/forums/w220-s-class/1688209-alternator-voltage-regulator-replace-diy.html
Acknowledgement – W220 Generator / Alternator / Charging System
With thanks to BenzWorld members cmitch, Check Codes, et alia, with apologies.