A BMW E46 alternator replacement may be needed if your dashboard battery light is on and you start losing electronics while the engine is running.
- Since you will be working on the vehicle's electrical system it is critical that you disconnect the negative terminal from your battery before starting. Not disconnecting your battery can cause catastrophic damage to sensitive electronics.
- Remove the intake snorkel from the front of the car. It is held in place with two plastic rivets.
- Using a 10mm socket wrench, remove the two bolts anchoring the intake muffler to the vehicle. Unclip the intake muffler from the mass air flow (MAF) sensor and remove it from the vehicle.
- Next, the upper radiator hose needs to be removed. Use a metal pick or flat blade screwdriver to release the two locking clips anchoring the upper radiator hose to the coolant expansion tank.
- Release the locking clip anchoring the hose to the thermostat.
- Grasp the hose and remove it from the vehicle. If the hose is stuck on one of the fittings, use a flat blade screwdriver to gently pry it off.
- Remove the air quality sensor and the wiring harness connection from the right side of the fan shroud.
- Remove the two fasteners anchoring the fan shroud to the front of the vehicle. These fasteners are often lost or changed over the years, so there may be screws, plastic rivets, or even zip ties holding the fan shroud.
- Carefully remove the plastic fan shroud, paying attention to the fan blades during removal. It helps to have someone underneath the vehicle press in on the bottom of the shroud so it clears the fan blades. Once the bottom of the shroud is clear of blades, it will pull out smoothly.
- With the fan shroud removed, you can now access the fan clutch nut. Use a BMW fan clutch tool to loosen the fan clutch nut. Remember...the fan clutch nut is a reverse thread! You must turn the nut clockwise (to the right) to loosen it. If you are able to loosen the nut with the tool, remove the fan and proceed to step 12. If you cannot loosen the nut with the tool, go to step 11.
- It is very common for the fan clutch nut on BMW E46s to seize and not be removable with the fan clutch tool. Lack of maintenance and poor maintenance practices (not greasing nut during prior repairs) causes stripped and seized nuts, making them virtually impossible to remove. Many nuts will show the battle scars of mechanics attempting to remove them...a telltale sign that trouble lingers ahead. Your only option at this point is to remove the fan clutch bolts and remove the plastic cooling fan. Use a T30 torx bit to remove the three fan clutch mounting bolts. Remove the fan from the vehicle.
- Next, the belt tensioner will need to be retracted so the main accessory belt can be pulled loose from the alternator pulley. Locate the belt tensioner pulley and remove its dust cap. Using a T50 torx bit, rotate the pulley counterclockwise until it releases its pressure on the main accessory belt.
- With the pressure removed from the main accessory belt, pull the belt off of the idler and alternator pulleys.
- The alternator is anchored to the engine with an upper and lower mounting bolt. The top bolt also serves as the idler pulley mounting bolt.
- Using a 16mm socket wrench, remove the idler pulley/upper alternator mounting bolt.
- Remove the lower mounting bolt with the 16mm socket wrench.
- Reach down and push the air cooling duct free from the alternator with your finger.
- Pull the protective rubber cap free from the positive battery cable connection on the back of the alternator. Using a 13mm socket wrench, remove the positive cable from the rear of the alternator.
- Grasp the alternator and rotate it away from the engine.
- Unplug the alternator sensor.
- The alternator can now be lifted off of its mount and removed from the vehicle.
BMW E46 Alternator Replacement Checklist
***The following steps were performed on a 2000 323i...other models may vary.-
- Place the new alternator in the car on its bracket.
- Plug the alternator sensor back in.
- Install the positive battery cable back on the alternator. Torque the mounting nut to 25 Nm (18 ft-lb).
- Reinstall the air cooling duct to the bottom of the alternator.
- Replace the upper (idler pulley) and lower mounting bolts and torque to 50 Nm (25 ft-lb).
- Replace the main accessory belt.
- Replace the cooling fan. If you were able to remove the fan by loosening the fan clutch nut, apply some grease to the threads before reinstalling (this will prevent the nut from seizing up and make future fan removals go easy).
- Reinstall the fan shroud.
- Reinstall the wiring harness connection and air quality sensor back on the fan shroud.
- Replace the upper radiator hose. BE VERY SURE that you hear the hose connections click onto their fittings.
- Install the intake muffler.