Usual symptoms: engine stalls on idle or poor idle; Check Engine error light will also be on, poor fuel economy
My Peake tool confirmed that my PreCat O2 Sensor has failed.
As per recommended BMW maintenance schedule, this part is also recommended to be replaced every 100K miles.
Chock the car both ways. Please take all the necessary precautions.
Use a ramp to raise the front of the car, or use a Jack.
Under the car, about mid-front door, you will see this black box.
Use a 10mm Socket wrench to take out the 2 bolts that secure this box to the frame.
Open this box and disconnect the Pre-Catalytic Converter Oxygen Sensor
Use a small flat-head screwdriver to pry out the connection from its locking tabs.
Pull out and disconnect.
Trace and follow the other end of this disconnected wire back to the Pre-Cat O2 Sensor. You will need to unscrew this sensor using a 22mm Socket Wrench.
NOTE: I had a hard time loosening this sensor out using the socket wrench. I did not have enough leverage underneath. Instead, I used a 22mm Flared Nut Wrench to loosen it with the aid of a hydraulic jack. I also applied penetrating oil to loosen it.
Once loose, we should now even be able to use our fingers to unscrew it.
Here's a pic of the new part and the old part.
Wipe out the excess penetrating oil with a rug.
Install the new Pre-Cat O2 Sensor and tighten.
Connect the O2 Sensor back to the wiring harness
Align connectors and snap tab into place.
Snap back connectors in place into the protective box
Reattach the protective box by securing it back to the car frame using the 2 10mm bolts
Secure back the wiring harness into locking tabs.
Now will be the good time to reset your fault codes and the "Check Engine" light error.
Pop the hood up and locate the access port. Unscrew and open up the cap.
Take note of the aligning notch.
Align your Peake R5/FCX Reset Tool with the aligning notch of the port and insert the tool in place.
NOTE: You do not need to twist the tool to seat it into place.
Proceed to reset fault codes.
Consult your Peak Reset Tool manuals for procedure.