Changing the front o2 sensor for the 335i N54 is not for the weak at heart, arguably one of the more difficult sensors to change due to its inaccessibility.
Today we are changing the bank 1 sensor 1 only. However, I highly recommend changing both BANK 1 and BANK 2 sensor 1's at the same time.
A couple of the crucial tools that you will need to finish the job properly. Note: You may or may not need more or fewer tools depending on your mechanical skill.
10mm socket
8mm socket
17mm socket
16mm wrench
22mm wrench
Flathead Screwdriver (for prying)
t10 torx
7/8 O2 sensor socket (optional)
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Start with lifting the car up on JACK STANDS, and remove the Passenger side wheel for easier access.
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Remove the splash shield using the 8mm socket.
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Remove the cowl cover for easier access to the pre-cat o2 sensor wire route.
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The yellow line represents the route of the BANK 2 Sensor 1.
The orange line represents the route of the BANK 1 Sensor 1.
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The Black loom is the Bank 1, grey is Bank 2. It wraps behind the valve cover.
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Time to go under the car.
Now it may sound crazy at first when you are only here to replace the O2 sensor but it must move. You have to remove the 2 bolts that attach the steering rack to the frame.
Place the 16mm wrench on the top nut(stop it from spinning). The bolt is 10mm (odd? yes i know)
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Moving the steering rack aside, keeping the tie-rods attached to the wheel hubs. This will NOT ruin your alignment don't worry.
Now you have access to the BANK 1 and BANK 2 pre-cat sensors. I recommend using a long 22mm wrench or the 7/8 "box end" style o2 sensor socket.
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Compare the new to the old to make sure its the correct sensor.
Assembly is the opposite Disassembly.
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THEN YOU ARE DONE!
Not that hard when you do it once. Now you are ready to destroy the Cheap-Class.
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