These photos are of the drivers side (USA) pre-cat O2 sensor, but all four sensors attach the same way. The only difference is the post-cat O2 wires are longer and held to the car by metal clips.
Get the front of your car on ramps/jacks/lift. I also used floor jacks on my rear to give a little more wrenching room.
View attachment 939190
Prepare a breaker bar. This is a 22mm (aka 7/8ths) O2 socket on an 18in breaker. If you don't have that socket a 22mm crows foot would also work. The small ratchet has a 10mm socket to remove the wiring box covers.
View attachment 939193
Here's a shot of the pre-cat O2. The front of the car is to the left. Hopefully your breaker bar gets it loose.
View attachment 939194
Here's the wiring box. The front of the car is to the right and the post-cat wire is coming in from the upper left. The two 10mm nuts need to come off.
View attachment 939195
Here’s the open box flipped over. The front of the car is to the right. The pre-cat O2 sensor plug is pressure fit to the wiring harness connector you see at the top of the photo. The connection pulls straight out of the cover. Pull the connector halves apart firmly to disassemble.
View attachment 939196
You should install the new sensor and torque it down before you reattach to the wiring harness. Also check each bung weld for fractures which some members have found. Cleaning it with a wire brush first helps.
View attachment 939198
The connector is keyed. It only plugs in one way. The connector will not give a satisfying 'click' when reassembled. The part number is for pre-cat only.
View attachment 939197
View attachment 939202
Here are my old (75k miles) O2's. The plastic cap comes on the tip of the new sensors. Under it is a measured amount of OEM anti-seize. Do not remove the cap until you're about to install so you don't lose any.
View attachment 939199
Prepare your torque wrench. The torque setting per the manual is 50Nm. The sensors have a crush washer similar to spark plugs so it'll take a bit of turning before it snugs up tight. Any attachment (like my crows foot) that effectively changes the length of the wrench requires a little math. This 'simple' formula is at the end of this DIY for reference. My number dropped from 50Nm to 45Nm to make up for the increased lever length. It probably doesn't matter too much since this is a steel on steel connection with pretty big threads.
View attachment 939201
That's all there is to it really. Good luck!
The formula:
T(W) = T(E)* L/L+E
L - Lever length of the wrench - center of the hand grip to center of the drive head (where sockets attach). (14.5in)
E - Effective length of extension. (1.5in)
T(E) - Torque applied by the extension to the fastener.
T(W) - Torque set on the wrench.
I'll use my (lengths) as an example.
45 = 50*(14.5/14.5+1.5)
Inside the ()'s I wound up with ~.90...multiplied that by the extension torque I wanted applied (50Nm) and you see that my wrench needed to be set to ~45Nm to compensate to the extra lever length the crows foot provided. The formula assumes the extension and wrench are assembled in a straight line as pictured.
Get the front of your car on ramps/jacks/lift. I also used floor jacks on my rear to give a little more wrenching room.
View attachment 939190
Prepare a breaker bar. This is a 22mm (aka 7/8ths) O2 socket on an 18in breaker. If you don't have that socket a 22mm crows foot would also work. The small ratchet has a 10mm socket to remove the wiring box covers.
View attachment 939193
Here's a shot of the pre-cat O2. The front of the car is to the left. Hopefully your breaker bar gets it loose.
View attachment 939194
Here's the wiring box. The front of the car is to the right and the post-cat wire is coming in from the upper left. The two 10mm nuts need to come off.
View attachment 939195
Here’s the open box flipped over. The front of the car is to the right. The pre-cat O2 sensor plug is pressure fit to the wiring harness connector you see at the top of the photo. The connection pulls straight out of the cover. Pull the connector halves apart firmly to disassemble.
View attachment 939196
You should install the new sensor and torque it down before you reattach to the wiring harness. Also check each bung weld for fractures which some members have found. Cleaning it with a wire brush first helps.
View attachment 939198
The connector is keyed. It only plugs in one way. The connector will not give a satisfying 'click' when reassembled. The part number is for pre-cat only.
View attachment 939197
View attachment 939202
Here are my old (75k miles) O2's. The plastic cap comes on the tip of the new sensors. Under it is a measured amount of OEM anti-seize. Do not remove the cap until you're about to install so you don't lose any.
View attachment 939199
Prepare your torque wrench. The torque setting per the manual is 50Nm. The sensors have a crush washer similar to spark plugs so it'll take a bit of turning before it snugs up tight. Any attachment (like my crows foot) that effectively changes the length of the wrench requires a little math. This 'simple' formula is at the end of this DIY for reference. My number dropped from 50Nm to 45Nm to make up for the increased lever length. It probably doesn't matter too much since this is a steel on steel connection with pretty big threads.
View attachment 939201
That's all there is to it really. Good luck!
The formula:
T(W) = T(E)* L/L+E
L - Lever length of the wrench - center of the hand grip to center of the drive head (where sockets attach). (14.5in)
E - Effective length of extension. (1.5in)
T(E) - Torque applied by the extension to the fastener.
T(W) - Torque set on the wrench.
I'll use my (lengths) as an example.
45 = 50*(14.5/14.5+1.5)
Inside the ()'s I wound up with ~.90...multiplied that by the extension torque I wanted applied (50Nm) and you see that my wrench needed to be set to ~45Nm to compensate to the extra lever length the crows foot provided. The formula assumes the extension and wrench are assembled in a straight line as pictured.
Special O2 sockets do exist though with a slot down one side to let the wire out. I will add that the whole system is recessed under the car and a socket may have been harder to use. That dimpled heat shield is pretty close to the end of the sensors where the wire comes out. An O2 socket + torque wrench might be a tight fit, but I'm not 100% on that. The crows foot eliminates that possibility.
