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Pelican Technical Article:

Alternator Replacement

Nick Czerula

Time:

3 hours3 hrs

Tab:

$300

Talent:

***

Tools:

Set of sockets, 17mm open-end wrench, flathead and Phillips screwdrivers, needle-nose pliers

Applicable Models:

BMW 323Ci Coupe/Conv (1999-00)
BMW 323i Sedan/Wagon (1999-00)
BMW 325Ci Coupe/Conv (2001-06)
BMW 325i/xi Sedan/Wagon (2001-06)
BMW 328Ci Coupe (1999-00)
BMW 328i Sedan (1999-00)
BMW 330Ci Coupe/Conv (2001-06)
BMW 330i/xi Sedan (2001-06)

Parts Required:

Alternator, drive belt, idler pulley

Hot Tip:

Work with a cool engine

Performance Gain:

Car will charge properly

Complementary Modification:

Change serpentine belt, idler pulley

The electrical system in your vehicle is powered by a 12-volt battery. The initial job of the battery is to power the starter motor, thus cranking the engine fast enough to start. The battery also supplies voltage to the ignition system, the fuel system, lights, HVAC system, windows, door locks and multitudes of other components that consume the available electrical power throughout the car. In order to maintain the battery in a state of charge, a belt-driven electrical generator, generally referred to as an alternator, is bolted to the engine block. The belt driving the alternator is powered by the engine pulley (vibration damper). As soon as the engine starts, electrical power is generated by the alternator and supplied to the battery to recharge it.

Generation of electricity creates a significant amount of heat in the inner windings of the alternator. This heat needs to be vented and dispersed in order to prevent damage to the alternator. Air-cooling of the alternator is used in nearly all car models and most BMW models.

A faulty or failing alternator can cause many problems; from a simple discharging of the battery to an engine drivability problem. There are a few signs and tests you can perform to determine if the alternator is the root cause of your problem. If you get lucky, your battery light (charging system indicator) will illuminate to warn you of a possible failure. When the battery light (charging system indicator) is ON, this means a voltage difference has been detected between battery positive (+) constant (terminal 30) and the ignition ON circuit (terminal 15), indicating a fault in the charging system.

It is common for an alternator to fail slowly. When this happens, your symptoms will be present when the electrical system has the highest load, like at night. Driving at night, you may notice the instrument panel lights dim, the radio or headlights flicker. This is a good indication that the alternator cannot handle the excess load.  Another indicator of a charging system problem is that the headlights or the radio volume will be lower when lowering or raising your electric window. When the alternator can no longer charge the battery, you may park your vehicle and not be able to start it. Of course, this could be a faulty battery too.

Check the voltage of your charging system under load. Voltage should be within 13.2 - 14.5 volts dc. To load, have the engine running at idle, turn on the headlights and HVAC blower motor. Do not disconnect a battery cable while the engine is running to test the alternator. You may cause damage to the alternator or other electrical components from the surge in amperage. Before performing any tests of your alternator, charge and test your battery. If the battery is faulty, your alternator tests will not be accurate.

In this article, I will go over the steps involved with replacing the alternator on the BMW M52 and M54 engines. Be sure to work with a cool engine and disconnect the battery before beginning. E46 models were equipped with a few different alternators with differing amperage ratings. Be sure your replacement alternator has the same rating as the faulty unit. You can usually find the amperage rating on the alternator housing. 

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches. 

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you are working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability. 

Vehicle models change and evolve as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Working in the trunk, disconnect the battery negative cable and cover the battery terminal so that the cable does not accidentally come in contact with the disconnected cable. See our Tech Article on how to disconnect your battery for more info.

BMW E46 models utilize 2 multi-rib engine drive belts driven by the crankshaft.
Figure 1

BMW E46 models utilize 2 multi-rib engine drive belts driven by the crankshaft. Automatic tensioners are used to maintain belt tension and an idler pulley is used on the accessory belt to achieve proper belt wrap. Mark direction of belt rotation before removing if reusing belt. When replacing alternator, you only have to remove alternator drive belt from alternator pulley and move aside, it does not have to be removed from the engine.

Working at the top of the radiator, remove the expansion rivets from the intake air duct (yellow arrows).
Figure 2

Working at the top of the radiator, remove the expansion rivets from the intake air duct (yellow arrows).

To remove the rivets, you can use a the small flathead screwdriver to pry them up, then using needle-nose pliers, pull the rivets out.
Figure 3

To remove the rivets, you can use a the small flathead screwdriver to pry them up, then using needle-nose pliers, pull the rivets out. The expanding portion of the rivet will now come out with duct. Depending on model year, vehicle may have 3 or 4 expansion rivets.

Next, remove the intake air duct from radiator support by lifting up and out of the intake air housing duct.
Figure 4

Next, remove the intake air duct from radiator support by lifting up and out of the intake air housing duct.

Remove the engine drive belt from the alternator pulley and lay it aside.
Figure 5

Remove the cooling fan shroud. See our Pelican Parts Technical Article on Removing the Radiator Fan.

Remove the engine drive belt from the alternator pulley and lay it aside. See our Pelican Parts Technical Article on Replacing Your Drive Belts.

Remove the air filter housing assembly fasteners (yellow arrows) and disconnect the air flow meter electrical connector (green arrow).
Figure 6

Remove the air filter housing assembly fasteners (yellow arrows) and disconnect the air flow meter electrical connector (green arrow).

Loosen the air flow meter clamp (green arrow), then disconnect the duct from air flow meter and remove the air filter housing from the engine compartment.
Figure 7

Loosen the air flow meter clamp (green arrow), then disconnect the duct from air flow meter and remove the air filter housing from the engine compartment.

Working below the alternator, disconnect the cooling duct (yellow arrow).
Figure 8

Working below the alternator, disconnect the cooling duct (yellow arrow). Grasp the duct and pull it away from the alternator while rocking it back and forth.

Working at the back of the alternator, disconnect the electrical connector (yellow arrow).
Figure 9

Working at the back of the alternator, disconnect the electrical connector (yellow arrow). Then remove the alternator positive (+) cable fastener (17mm) (green arrow), and remove the cable from the alternator.

Working at the top of the alternator, remove the idler puller dust cap.
Figure 10

Working at the top of the alternator, remove the idler puller dust cap.

Then loosen the idler pulley bolt.
Figure 11

Then loosen the idler pulley bolt.

Slide the bolt out of the alternator and remove the pulley from the engine.
Figure 12

Slide the bolt out of the alternator and remove the pulley from the engine.

Working at the bottom of the alternator, loosen lower alternator mounting bolt (green arrow).
Figure 13

Working at the bottom of the alternator, loosen lower alternator mounting bolt (green arrow).

Then remove the lower alternator mounting bolt.
Figure 14

Then remove the lower alternator mounting bolt.

Next, remove the alternator from the mounting bracket by rocking it back and forth while pulling it up and off the bracket.
Figure 15

Next, remove the alternator from the mounting bracket by rocking it back and forth while pulling it up and off the bracket. Once you wiggle it out of the mounting bracket, remove the alternator from the engine compartment. Before installing the alternator, it is a good idea to check the alternator cooling duct for debris, leaves and other road debris that can get trapped in the duct, preventing proper alternator cooling. This could lead to an overheated alternator and a charging system failure.

If reinstalling an old or used alternator, you may have to move the bushing (green arrow) out of mounting ear for proper a fit unto the alternator bracket.
Figure 16

If reinstalling an old or used alternator, you may have to move the bushing (green arrow) out of mounting ear for proper a fit unto the alternator bracket. To do this, thread the bolt into the bushing, and then place a 24mm socket under the bushing, using a small hammer to tap it lightly to drive the bushing flush with the mounting ear. Be very careful and do not use too much force, damage to alternator may occur. Install the alternator in the alternator bracket.

Install the idler pulley through the alternator and fasten it to engine.
Figure 17

Install the idler pulley through the alternator and fasten it to engine. Check that the idler puller alignment tab is properly aligned with the notch in the alternator. Torque the bolt to specs. Tighten the lower alternator fastener. Connect the electrical connector at rear of the alternator and the install positive cable to alternator, torquing it to specs. Install the alternator cooling duct.

Next reinstall the drive belts (see our Pelican Parts Technical Article on Replacing Your Drive Belts for more information). Reassemble the radiator cooling fan, air filter housing, and intake air duct. Connect the battery negative cable. Check the operation of the charging system and alignment of the drive belts.

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Comments and Suggestions:
POS M3 Comments: I checked the drop voltage of the + and -, 0.0V. I had the battery checked at O'Reiley Auto good in the last quarter of its life and alternator checked good 3 times in a row. I now believe the problem is a parasitic drain. After 16 minutes of rest, my car is at 40mA which I read is normal. I am wondering if something "wakes" my car at random times. I currently have fuse #41 pulled and I'm monitoring the voltage. Any other thoughts out there?
August 8, 2016
  Followup from the Pelican Staff: If you have a parasitic draw. You'll want to monitor the draw on the battery when the vehicle is asleep. Here is a list of the specifications: http://autotechdiagnostics.com /?p=185
Once you confirm there is a draw. You will have to isolate the circuit with the draw. Then determine which components on that circuit is causing the draw You can isolate by removing fuses. be sure to have all the latches on the doors and hood closed (pin switches) so the vehicle will sleep during testing. If it wakes up, you will have to wait until it goes to sleep again.

if you believe it is waking, you can perform an energy diagnosis test if the vehicle is new enough, or just record the draw using a recording meter.
- Nick at Pelican Parts
 
POS M3 Comments: I have a 2004 M3, I tested the sleeping current, 0.04 amps after 16 minutes, operating voltage across + and - while idling is 13.5 V. I let it run for an hour to charge the battery after jumping it. Within 20 minutes of shutting the car off, the battery measured 12.4 and would barely start. I have a new battery, less than 4 months old. I did have the negative come off of the battery while driving. I reconnected the battery and the car worked fine. I have no engine lights on but the radio has been turning off although the navigation continues to work. I removed the radio and drove the car for a day, it finally would not start, I installed the radio, and then it started. Any thoughts?
August 1, 2016
  Followup from the Pelican Staff: 12.4 is a good battery. I would imagine you have a bad connection. I would voltage drop test the battery cables, positive and negative. - Nick at Pelican Parts  
Alpaca Comments: Easiest way to check if you have alternator issue is to check battery voltage with the car off at 11.8V battery is drained and car won;t start anymore - so you can charge battery and try again - then check voltage with engine running if alternator is good, should read 13-14V or so. In my case, alternator fried - and of course car keeps running as long as battery lasts - and when voltage drops low enough - all sorts of warning lights come up on the dash - looks like a Christmas tree - good time to pull over and test battery and alternator voltage !

Hardest part of this job is removing the cooling fan to get access to the drive belts - there is special tool that makes it easier - but I was able to do with adjustable wrench and pry bar - there is youtube video you can find that shows you how to do this. Make sure you get the alternator with the right plug - my 2003 does not have any of the cooling ductwork not sure if the car came like that or a previous mechanic removed it. Also, might as well replace both drive belts while you are doing this.
December 21, 2015
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
Dog Comments: Nice write up and photos. After doing this job today, I'd point out that step one should be removal of the belt from the alternator. It's implied but not explicitly written. The belt will hang from the crankshaft pulley and won't come off the car as mentioned. Tension needs to be removed before the idler and alternator are unbolted.
December 19, 2015
  Followup from the Pelican Staff: It is mentioned in step 1:

BMW E46 models utilize 2 multi-rib engine drive belts driven by the crankshaft. Automatic tensioners are used to maintain belt tension and an idler pulley is used on the accessory belt to achieve proper belt wrap. Mark direction of belt rotation before removing if reusing belt. When replacing alternator, you only have to remove alternator drive belt from alternator pulley and move aside, it does not have to be removed from the engine.

You can find the belt procedure in our drive belt tech article. - Nick at Pelican Parts
 
goose Comments: have a 2005 bmw 325i, trying to replace alternator but plug is wrong on new one twice now, also do i have to remove fan which looks like a clutch fan
October 24, 2015
  Followup from the Pelican Staff: The cooling fan clutch?

Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
ramaney Comments: I have a 2000 BMW 318i M-Sport and i have replaced the alternator because parentally it was not charging the battery after replacing the battery twice. It is still not starting unless i jump start it, even when i jump start it, it does not have much power in it unless i put it into manual mode when the temperature is cold, when its warm then it goes fine. what can i do next? please help! not ready to give up on my car just yet :
June 13, 2015
  Followup from the Pelican Staff: I would test the battery and charging system. Check charging voltage and current under load. You may still have a charging system issue. - Nick at Pelican Parts  
dee Comments: i have a 2004 bmw 325 xi and i am replacing the alternator would 120 voltage be the alternator to buy?
June 8, 2015
  Followup from the Pelican Staff: you mean amperage? You need to match the one that comes out. Just buy the correct part number for your vehicle. Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Tony Comments: I have a 2004 325i BMW my check engine light is on. Recently the EML light came on the car wouldn't go over 20 mph. I replaced the throttle body and its driving a little better with the EML Light off. Now when I drive forward I have to press the pedal further down to the floor than usual. The car drives sluggish & gas goes fast. the alternator signal is implausible. oil pressure switch signal is implausible ?? Help....

Is it worth replacing the alternator??
May 5, 2015
  Followup from the Pelican Staff: If you suspect the alternator is the cause, I would check charging system voltage and current. You need to confirm it is the root cause.- Nick at Pelican Parts  
Marg Comments: Also abs lights on air con not working all happening after driving for 15 minutes ...marg
May 2, 2015
  Followup from the Pelican Staff: You may have lost a drive belt. I would take it to your shop right away. - Nick at Pelican Parts  
Marg Comments: Just had my car BMW series1 year 2005 serviced and one day later the alternator isn't working I had on sign that it was failing - can it be anything to do with getting it serviced.
May 2, 2015
  Followup from the Pelican Staff: Depends on what was serviced. - Nick at Pelican Parts  
Nerve Comments: Thank you for a wonderful guide and walk through. very much appreciated.
April 5, 2015
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help. - Nick at Pelican Parts  
idickers Comments: I dropped one of the bolts that holds the cap to the back of the alternator. The remaining bolt does not match up to any bolt in my spares box, and is not listed on realoem or the at dealer. It looks like an M5 bolt, any idea of the thread pitch? It's not 0.8.
January 22, 2015
  Followup from the Pelican Staff: I am not sure. Give our parts specialists a call at 1-888-280-7799. They can help you find the right part.
- Nick at Pelican Parts
 
A5m1ffy Comments: I have a 325ti I have just upgraded my alternator to a 180amp from a 120d however my old alt had 2 wires number 1 and number 2. The new alt only has 1 connection which do I use? Thanks
September 30, 2014
  Followup from the Pelican Staff: I don't have the wiring for those alternators.

I opened a post in our forums. A Pelican community member may be able to answer your question.
- Nick at Pelican Parts
 
Vic Comments: Nick, thanks for the follow up. I took it to the shop and it was the alternator. It was a quick and easy fix
July 17, 2014
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
 
Vic Comments: I have a 2004 325i and yesterday several lights on the dashboard decided to light up all at once. My a/c would work intermittently, the abs light was on, the service engine soon light was on and the vehicle speedometer fluctuated, the car also drove like it didn't want to go anywhere at times. I had to give the car a jump in order to get it started. Please tell me what the problem could be so I can at least have a clue when I take it to the repair shop. Thanks
July 13, 2014
  Followup from the Pelican Staff: COuld be as simple as a charging system issue. I would start there. Then, check the vehicle for fault codes. If multiple systems are not working properly, fault codes will be set. This will be your best bet when diagnosing.
- Nick at Pelican Parts
 
SAINY Comments: MY 325 CI IS GIVING A FAULT CODE AS VOLTAGE PROBLEM CAUSING GEARBOX TO GO INTO LIMP MODE THEY SAY THE ALTERNATOR VO;TAGE IS TOO HIGH 16VOLTS IS THIS POSSIBLE
April 16, 2014
  Followup from the Pelican Staff: Yes. I would check charging system voltage. - Nick at Pelican Parts  
tonyp Comments: My 2002 325i just happens to only have one wire green coming out of the altetnator plug harness. Id like to know if it is supposed to be like this or should it have a second wire leading to the second pin. & where does this plug harness connect to from the other end? Thsnk you.
January 11, 2014
  Followup from the Pelican Staff: One is likely normal. - Nick at Pelican Parts  
CABMW Comments: I was able to fix my alternator on my 2001 330i without removing it from the car. I installed a new regulator which comes with new alternator brushes part no. 12-31-7-551-153-M262. This was a quick and easy fix.
June 20, 2013
  Followup from the Pelican Staff: Thanks for the info and feedback. - Nick at Pelican Parts  

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