• BMW OBD2 Scan Tool
• Appropriate Size Fuse
• Fuse Removal Tool
• 8MM Socket

Using a BMW capable scan tool, scan for engine codes. If all of your O2 Sensors are showing bad at once, this DIY guide should fix your issue.

Codes: P0031 P0037 P0051 P0057

Disconnect the vehicle's battery to ensure safety while conducting this job.

Open your vehicle's hood by pulling the latch.

Remove the cabin air filter, HVAC cowl and all covers in the way of accessing the ECU. You should only need an 8MM socket for this.

Locate your BMW's ECU. On LHD vehicles, it will be on the passenger side under the HVAC cowl. On RHD vehicles, vice versa.

Unlock the ECU by sliding the locking latch to the left.

Unlatch the ECU cover by pressing/pinching the retention tabs inwards. This will completely loosen the cover so you can remove it.

With the ECU cover loosened, simply lift to remove it.

Locate the fuse box pictured above. This fuse box contains the fuse that controls all four O2 sensors.

Unlatch the fuse box by pulling up and unseating the retention clip.

Unseat the fuses by pulling them apart from the female end of the box.

Unlock the fuse box lid by using a pick tool to depress the retention clips (circled) and slide the lid back.

Remove and replace the fourth fuse down. This fuse controls all four O2 sensors and typically shorts out if any mechanical work has been done.

Re-install the fuse box after replacing the blown fuse. Simply put the lid back on and press the fuses back into place.

Reinstall the ECU cover by re-latching and locking it into place.

Re-install all components in the vice versa of removal. i.e cabin air filter and cowl, covers etc.

Reconnect your BMW's battery.

Using a BMW scan tool, confirm all O2 sensor related codes are gone. Note you may have to clear any pre-existing codes, so don't be concerned if you see any present at first.

Good job replacing your alternator! Be sure to keep an eye on your electrical system for any future issues.