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Mercedes Voltage Regulator Replacement
 
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Pelican Technical Article:

Mercedes Voltage Regulator Replacement

Steve Vernon

Time:

2 hour2 hr

Tab:

$40

Talent:

**

Tools:

10mm, 13mm, 15mm sockets, Philips head screwdriver

Applicable Models:

Mercedes-Benz W203 (2001-07)

Parts Required:

New Voltage Regulator

Hot Tip:

ALWAYS disconnect the battery before beginning

Performance Gain:

Car charges again

Complementary Modification:

Change serpentine belt

The alternator charges the battery and provides your car with a constant source of electricity while the engine is running. The voltage regulator does just what it says: it regulates the voltage from the alternator. Your battery should read a little more than 12 volts with the engine off. Next check the voltage of your charging system under load, the voltage should be within 13.2: 14.5 volts d/c. To load, have engine running at idle, turn on headlights and HVAC blower motor. Never disconnect a battery cable while engine is running to test alternator, you may cause damage to alternator or other electrical components from the surge in amperage. If your battery appears to be leaking, then your voltage regulator has probably failed. The battery will usually only leak acid if it has been overcharged at a much higher voltage. If the voltage measured at the battery is more than 14.5 volts when the engine is running, then the voltage regulator is probably bad. If your battery has boiled over and has acid overflowing out the top, make sure that you clean up any spilled acid immediately. Dousing the area with a water and baking soda solution should help considerably to neutralize the acid, and prevent it from eating away at the metal.

A large amount of the time when there is an electrical problem with the charging system it is the voltage regulator yet people just swap out the entire alternator because it comes with a new voltage regulator included because it is easier, fixes the problem and most people do not understand how an electrical system works on their car. If your electrical issues are caused by a faulty voltage regulator you can save your self a lot of money by just replacing the defective part.

You will have to take the alternator out of the car to replace the voltage regulator. Please see our article on replacing your alternator. You must perform this work first.

Turn your alternator pulley side down on your bench. The voltage regulator is partially obscured by a plastic cover on the back of the alternator. Remove the two bolts (one 13mm and one 15mm) on the back and lift the plastic cover off.

With the cover off you will see the three Philips head screw that hold the regulator in place. Remove the three screws and lift the voltage regulator from the alternator.

You can now see the two "brushes" that make contact with the poles on the alternator. These are held in lace against the polls by springs that can wear out; the brushes can also wear out or become excessively corroded over time.

While the regulator is out make sure you check the condition of the poles on the alternator: they can be discolored but should not be excessively worn, corroded and should not have grooves worn in them.

Note: If you just look at this part of our articles to help you with your projects you will need have removed the alternator at this point. Please see our article on removing the alternator and then return here.

Turn your alternator pulley side down on your bench.
Figure 1

Turn your alternator pulley side down on your bench. The voltage regulator is partially obscured by a plastic cover on the back of the alternator. Remove the two bolts (red arrows, one 13mm and one 15mm) on the back and lift the plastic cover off.

With the cover off you will see the three Philips head screws (red arrows) that hold the regulator in place.
Figure 2

With the cover off you will see the three Philips head screws (red arrows) that hold the regulator in place.

Remove the three screws (red arrows) and lift the voltage regulator from the alternator.
Figure 3

Remove the three screws (red arrows) and lift the voltage regulator from the alternator.

You can now see the two â€Å
Figure 4

You can now see the two "brushes" (yellow arrows) that make contact with the poles on the alternator. These are held in place against the polls by springs that can wear out; the brushes can also wear out or become excessively corroded over time.

While the regulator is out make sure you check the condition of the poles (yellow arrow) on the alternator: they can be discolored but should not be excessively worn, corroded and should not have grooves worn in them.
Figure 5

While the regulator is out make sure you check the condition of the poles (yellow arrow) on the alternator: they can be discolored but should not be excessively worn, corroded and should not have grooves worn in them.

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Comments and Suggestions:
CHUCK Comments: Hello.. I have a 2006 c230 mercedes , was driving when I suddenly received a message on the dash reading "check battery alternator see workshop soon". My radio then read low voltage and stopped working. Car shortly after stalled, and now it won't start even after trying to jumpstart it. could this be VR, bad battery, or alternator?
September 11, 2016
  Followup from the Pelican Staff: Sounds like the alternator has failed. - Nick at Pelican Parts  
pernell Comments: I have 2001 clk430 mypassengr side tail light parking light wont come on but signal and brake light works.checked fuse box and changed bulbs.. what do uthink the prblem is
June 7, 2016
  Followup from the Pelican Staff: Check if the bulb is getting power or ground. It may be the socket.

Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Nilserikp Comments: This is a Google translation. I've changed the alternator and battery. The battery in the rest 13,4V. at start 12.5V. shortly after 18V. Idle 13.4V. 1500rpm 14.3V. After 3 ... 4 minutes remain 18V at any second. Since there seems to come more. During all the time warned of the brake lights do not work. Both right and left. other codes: ESP, SRS, and BAS have occurred. some suggestions to the problem? it may be the alternator is wrong even if it is new?
May 11, 2016
  Followup from the Pelican Staff: If voltage is rising, the internal regulator is faulty. i would replace the alternator. - Nick at Pelican Parts  
Auxois350 Comments: Hi,
I bought a 2004 C180 Kompressor, and ai test the charging. The results are those: When I start the engine, and it running idle 850-900 rpm I have 13.3V when I touch the cass pedal 1100-1200 rpm charging is 14.2V. If I drive the care about 20-30min, on load, charging is 13.7-13.8. On idle running is 13.3-13.4. It is normal or should I visit an electrician?
August 30, 2015
  Followup from the Pelican Staff: Sounds fine. - Nick at Pelican Parts  
Luis Comments: Is the voltage regulator the problem for my C240 when the alternator stops working after 3k RPM? Below 3k the alternator works fine, and I've changed the battery and alternator about a month ago with refurb alternator.
March 23, 2015
  Followup from the Pelican Staff: The replacement alternator sounds faulty. Check charging output, voltage and current. - Nick at Pelican Parts  
Deb Comments: How do I by pass and charge the battery from the bonnet on aS320 1999 model
November 30, 2014
  Followup from the Pelican Staff: Check your owner's manual for jump start connections, then attach jumper cables and see if that gets power to your vehicle. - Nick at Pelican Parts  
Debbie Comments: I can't get to my battery in the boot as the boot won't open and the battery is dead how do I by pass from the engine please
November 30, 2014
  Followup from the Pelican Staff: Have you tried opening the trunk with a key? That should allow access for you. - Nick at Pelican Parts  
David Comments: Issues with my 300td 83 not having a constiant voltage.
I have an onboard computerto control a HHO unit that shuts off at 13.2 v
I replaced the alt with a 120amp one 55 before
I have added a thicker wire from alt to batery
I have swaped all the wire out and re done all conections.
Is there something else that isnt letting my voltage stay around 13.8?
November 10, 2014
  Followup from the Pelican Staff: The voltage regulator will control voltage dependent on load. You may not have the load for that extra 0.1 volt. Have you checked charging voltage and current? - Nick at Pelican Parts  
Rami Comments: Hi I have a 1999 Mercedes-benz E320 ,
it has electrical problem , the dash light flickering and strong , abs ets esp , radio , shutdown intermetly ,

I did an alternator test with a voltmeter , it gives me more than 15V when I press the gaz , so I thought it is the voltage regulator and that means also that the voltage is soo high that means the alternator is charging well ,BUT ,
I replaced the voltage regulator and I was surprised , I had dim light and the voltage never reach 12V less than 12 v but stable even with high engine RPM, the battery not charging.
Does this a faulty new voltage regulator ?? with the old voltage regulator , the voltage was not stable like the new one but the voltage reaches more than 16V when I press the gaz ??!!!!!
should in replace the alternator or is it a faulty new voltage regulator?

Thanks a lot
October 29, 2014
  Followup from the Pelican Staff: It may be overcharing, which is bad. Check the charging system at idle and under load. If it is over 15 volts, the alternator may be faulty. - Nick at Pelican Parts  

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