Oxygen sensors have a limited life-span. Audi recommends replacing them every 60K miles. If your gas mileage has plummeted or you've failed an emissions test, you might want to consider replacing your old O2 sensor. The official replacement has the correct wires to mate up with the harness, but it's also over $100. You can get a generic three-wire sensor for much less, and just splice the wires into the existing ones. One common version is Bosch P/N 13913 and costs about $40. It's for some model of Ford and can be found at most auto parts stores, just ask for it by the P/N. If you prefer to have the original connector, you can get either Bosch P/N 13957, or NGK P/N 25040 (double-check these numbers to be sure).
Here are some instructions for replacing the sensor: (rngmeister)
- Disconnect negative battery terminal.
- Disconnect the two plugs from their carriers on the driver's side of the block, just to the right side of the carrier for the plug wires.
- Remove battery and pop out silver insert from underside of tray (optional, but helps with the view--may not be necessary if your sensor is in the cat rather than the downpipe).
- Tie a string around the plug, so when you pull it through, you can attach the new wiring and direct it back through the same way with relative ease.
- Jack front of car up, turn wheels left to lock.
- Remove passenger side front wheel. This should give you access to the sensor, which is in the exhaust downpipe or in the front of the cat.
- There are a couple of stays that keep the wires in place; open them up, then pull the wires through and untie the string.
- Loosen and remove the old sensor. You can use a 22mm offset open-end or a box-end wrench, or you can buy a special O2 sensor socket that has a cutout in the side for the wires.
- Wipe off the downpipe so you can install the new sensor without getting any crud on the threads. The new sensor should come with anti-seize lube on the threads. If yours doesn't make sure you put some on!
- Install the new sensor and tighten to 37 ft-lbs.
- Tie the plug/wires to the end of the string and re-route them up to the holder. Tighten stays to keep wire in place, making sure if there is any extra (there might be a longer wire than the original) it is out of the way of any heat/moving parts.
- Plug it back up and secure in the plug carriers.
- Replace wheel, lower car down, replace battery and tray insert, connect cable.
- Fire it up and enjoy your smoother running, better gas mileage, and cleaner emissions.
Can I just say, what a pain in the ass it was to try and get that sucker off. It must have last been changed at 100k, I'm at ~255k.
New O2 Sensor
Old O2 Sensor
Comparison
My favorite part. Apparently the previous owner or two LOVED duct tape. I have replaced duct taped hoses all over the car. This takes the cake, and quite honestly makes me quite upset.
Yes...that is duct tape on the wiring to the O2 sensor...
The O2 sensor opening, from the battery viewing point.
Battery removed.
