What was supposed to be a simple day installing my catless headers turned into a bit of a detour. I went to start the car and… nothing. Completely dead.

Turns out the alternator had been undercharging the battery for a while, and letting it sit definitely didn’t help. So, before I could think about more power mods, it was time to handle some good ol’ BMW maintenance.

I managed to source a used OEM replacement locally and got to work.

Removal

This isn’t a full DIY guide, but here’s the basic rundown if you’re doing this on an M54-powered E46:

  1. Remove the fan and intake to access the front of the engine.
  2. Release tension and remove the serpentine belt.
  3. Remove the idler pulley.
  4. Unplug the electrical connector on the alternator.
  5. Remove the 17mm nut holding the positive cable.
  6. Pull the alternator out — it may need a bit of wiggling.

Here’s a proper diy guide for this.

Alternator Removed

Once it’s out, take a second to admire your hard work and the big gap left behind.

Installation

Reinstalling is as simple as reversing the steps. Make sure to torque everything properly and reconnect all electricals securely.

While I was in there, I also replaced the battery ground cable — mine was corroded and overdue.

Alternator Installed

Tools Used

  • 17mm socket
  • 16mm socket
  • Ratchet and extensions
  • T25 Torx (for fan shroud)
  • Flathead screwdriver
  • Serpentine belt tool
  • Patience and cold hands
Time Taken Difficulty
~1 hour ⭐☆☆☆☆ (Easy)