Tool selection tips for oxygen (O2) sensor removal / replacement on E85’s and E86’s with the N52 engine. This is focused on TOOLS to change your sensors, not when you should change them. I don't have TIS, and I apologize if all of this is in it.
My tool choices (photo):
These are the wrenches I have used on my E86 with N52 engine. I labelled them on the photo as (1), (2), and (3) – in the order in which to try them. Not shown are a tall 22mm with a slot or the cut-down 22mm wrench used to hammer out “rusted in” post-cat sensors as I've had to do once (not my N52 BMW -
).
The preferred tool (1) is a very strong, precise, and slim design open end 22mm crowfoot socket (mine is Tekton™, ca. $15 US, linked at end). Do NOT go cheap, do not use a “flare” socket, you will need the open end. Have one of these on hand before you begin. Seat it squarely onto the O2 sensor, and try it to loosen sensors before going to the other tools.
Reasons to try this first : a) this wrench will fit under the pre-cat Bank 2 O2 sensor heat shield to avoid removing it, and b) it will most easily fit the post-cat O2 sensors between the manifolds. It needs to be a high-end socket and must fit precisely and squarely. I used it to remove* my post-cat sensors and to install and torque all four sensors, with the pre-cat Bank 2 heat shield in place.
* Note: My coupe is a rust-free, summer-only car. If (1) fails, move to more robust tools to avoid rounding your sensor.
My second tool (2) is a box end 22mm wrench modified by removing a large arc that allows it to pass directly over the wide shafts of the Bosch sensors. It’s more convenient than the dedicated O2 sensor socket, but undoubtedly not as strong. This could be choice two or three, because it takes time to make it from a standard wrench. It fits more conveniently than my third, dedicated tool for the post-cat sensors, but one can’t measure torque, and it’s not so useful for the pre-cat sensors, with little room to swing it.
The third tool (3) to use is the dedicated O2 socket, forged to impact grade. It has the advantage of a “flare” type design so that it grips the flats of the sensor better. But this design has a very narrow slot to pass around the senor wires, and the OE Bosch sensors on my N52B (early style, “silver top”) have high, wide shafts. This wrench will not fit over them unless the pre-cat Bank 2 sensor heat shield is removed. It is also frustrating to use on the post-cat sensors because of the awkward angles between the manifolds. Use it if the preferred crowfoot will not work.
How I got there (background):
I replaced all four original O2 sensors on my 2006 E86 3.0Si (N52 engine). Timing to replace was driven by age (nineteen years), parts pricing (great deal on 4 Bosch OE sensors), and concern over sensors corroded in place. Tales of woe by Z4Forum members with downstream sensors “welded” to the manifold bungs helped me decide to change before I encountered a similar issue. I was able to remove all four sensors without the drama I feared.
But BMW sometimes make strange choices, and one of those is the pre-cat Bank 2 oxygen sensor “heat shield” (see photo). It’s heavy stainless steel and fastens to the cylinder head with two 6mm E8 head screws, which are nearly blind from the top. Bending it up for access to the Bank 2 sensor is not really feasible (don’t ask how I know :wink: ). The shield and the long, wide shaft of the Bosch OE sensor prevent a dedicated 22mm sensor wrench from fitting. Removing the E8 screws meant disconnecting the strut tower-to-firewall brace and the large aluminum heat shield first – at least those E8’s are magnetic! For reinstallation I did what I think BMW should have done, and I slotted the rear hole to allow the rear screw to be started in place before installation.
In hindsight, the better solution is (1) : a top-line 22mm slim-design, precise crowfoot socket. I ordered this online and paused my job when I realized that my dedicated 02 sensor wrench and my self-modified 22mm box end wrench would not allow me to torque the new sensor even with the heat shield removed. I ended up using this wrench to successfully remove both exhaust sensors and install and torque all four O2 sensors.
I am in no way associated with Tekton™, but this is a link to the crowfoot socket I used:
https://www.amazon.com/TEKTON-Drive...+x+22mm+crowfoot+wrench,tools,120&sr=1-4&th=1
My tool choices (photo):
These are the wrenches I have used on my E86 with N52 engine. I labelled them on the photo as (1), (2), and (3) – in the order in which to try them. Not shown are a tall 22mm with a slot or the cut-down 22mm wrench used to hammer out “rusted in” post-cat sensors as I've had to do once (not my N52 BMW -
).The preferred tool (1) is a very strong, precise, and slim design open end 22mm crowfoot socket (mine is Tekton™, ca. $15 US, linked at end). Do NOT go cheap, do not use a “flare” socket, you will need the open end. Have one of these on hand before you begin. Seat it squarely onto the O2 sensor, and try it to loosen sensors before going to the other tools.
Reasons to try this first : a) this wrench will fit under the pre-cat Bank 2 O2 sensor heat shield to avoid removing it, and b) it will most easily fit the post-cat O2 sensors between the manifolds. It needs to be a high-end socket and must fit precisely and squarely. I used it to remove* my post-cat sensors and to install and torque all four sensors, with the pre-cat Bank 2 heat shield in place.
* Note: My coupe is a rust-free, summer-only car. If (1) fails, move to more robust tools to avoid rounding your sensor.
My second tool (2) is a box end 22mm wrench modified by removing a large arc that allows it to pass directly over the wide shafts of the Bosch sensors. It’s more convenient than the dedicated O2 sensor socket, but undoubtedly not as strong. This could be choice two or three, because it takes time to make it from a standard wrench. It fits more conveniently than my third, dedicated tool for the post-cat sensors, but one can’t measure torque, and it’s not so useful for the pre-cat sensors, with little room to swing it.
The third tool (3) to use is the dedicated O2 socket, forged to impact grade. It has the advantage of a “flare” type design so that it grips the flats of the sensor better. But this design has a very narrow slot to pass around the senor wires, and the OE Bosch sensors on my N52B (early style, “silver top”) have high, wide shafts. This wrench will not fit over them unless the pre-cat Bank 2 sensor heat shield is removed. It is also frustrating to use on the post-cat sensors because of the awkward angles between the manifolds. Use it if the preferred crowfoot will not work.
How I got there (background):
I replaced all four original O2 sensors on my 2006 E86 3.0Si (N52 engine). Timing to replace was driven by age (nineteen years), parts pricing (great deal on 4 Bosch OE sensors), and concern over sensors corroded in place. Tales of woe by Z4Forum members with downstream sensors “welded” to the manifold bungs helped me decide to change before I encountered a similar issue. I was able to remove all four sensors without the drama I feared.
But BMW sometimes make strange choices, and one of those is the pre-cat Bank 2 oxygen sensor “heat shield” (see photo). It’s heavy stainless steel and fastens to the cylinder head with two 6mm E8 head screws, which are nearly blind from the top. Bending it up for access to the Bank 2 sensor is not really feasible (don’t ask how I know :wink: ). The shield and the long, wide shaft of the Bosch OE sensor prevent a dedicated 22mm sensor wrench from fitting. Removing the E8 screws meant disconnecting the strut tower-to-firewall brace and the large aluminum heat shield first – at least those E8’s are magnetic! For reinstallation I did what I think BMW should have done, and I slotted the rear hole to allow the rear screw to be started in place before installation.
In hindsight, the better solution is (1) : a top-line 22mm slim-design, precise crowfoot socket. I ordered this online and paused my job when I realized that my dedicated 02 sensor wrench and my self-modified 22mm box end wrench would not allow me to torque the new sensor even with the heat shield removed. I ended up using this wrench to successfully remove both exhaust sensors and install and torque all four O2 sensors.
I am in no way associated with Tekton™, but this is a link to the crowfoot socket I used:
https://www.amazon.com/TEKTON-Drive...+x+22mm+crowfoot+wrench,tools,120&sr=1-4&th=1