bigtube1
03-23-2005, 01:33 PM
Here's my contribution. I replaced both pre-cat O2 sensors and it was not real easy. But it is doable.
Both are accessable from under the hood.
The drivers side is under the coolant resevoir. You must remove the three screws holding the res down. Unplug the electrical wire to it, and flip it over out of your way. You should be able to see the sensor on the exhaust pipe. Mine broke loose very easy. Good thing because it is pretty tight in there.
The passenger side is harder unfortunately. You have to remove most of the plastic air-intake assembly. There is a way to do it without removing completely.
You can barely see the sensor with light shining down on it. Once you find it, you can see you have to go at it from the small opening up against the firewall. You will likely need to cut the plastic wire retainers and move the wire bundles so your arm will fit through without scratching your arm up.
Loosening that one was much harder because my semi-open ended wrench's angle was such that I coundn't get much leverage. But I got it. A typical offset open-end wrench might work better there.
Don't bother with the special O2 sensor sockets they sell or loan you at the auto-parts store. You will have to use the open or semi-open ended wrenches.
My 90K mile A6 4.2 feels like it gained 30-40hp after doing this. Biggest differrence I ever felt on any car replacing O2 sensors. But one was shot(according to the codes) and the other had low readings.
Have fun!
Both are accessable from under the hood.
The drivers side is under the coolant resevoir. You must remove the three screws holding the res down. Unplug the electrical wire to it, and flip it over out of your way. You should be able to see the sensor on the exhaust pipe. Mine broke loose very easy. Good thing because it is pretty tight in there.
The passenger side is harder unfortunately. You have to remove most of the plastic air-intake assembly. There is a way to do it without removing completely.
You can barely see the sensor with light shining down on it. Once you find it, you can see you have to go at it from the small opening up against the firewall. You will likely need to cut the plastic wire retainers and move the wire bundles so your arm will fit through without scratching your arm up.
Loosening that one was much harder because my semi-open ended wrench's angle was such that I coundn't get much leverage. But I got it. A typical offset open-end wrench might work better there.
Don't bother with the special O2 sensor sockets they sell or loan you at the auto-parts store. You will have to use the open or semi-open ended wrenches.
My 90K mile A6 4.2 feels like it gained 30-40hp after doing this. Biggest differrence I ever felt on any car replacing O2 sensors. But one was shot(according to the codes) and the other had low readings.
Have fun!