These Audi turbocharged engines are fitted with 2 O2 (Lambda) sensors. The rear sensor only monitors the catalytic converter's efficiency, but the one we're replacing here, the front sensor, adjusts the fuel-to-air mixture. The ideal Lamda value for a petrol engine is 1, which equals to a FTA mixture of 14. Now, with these engines, the mixture is actually controlled by the ECU based on the MAF signal, but then fine tuned by the front O2 sensor. Thus a car with a faulty or ”lazy” front O2 sensor will use up more fuel and lack power because the FTA mixture is wrong.
The OEM sensors in our cars are manufactured by Bosch and should always be replaced by Bosch units to prevent error codes, etc. The one I'm using here is specifically meant for the 1.8t and comes with all the correct connectors, etc. To facilitate plug-n-play installation. Bosch recommends you 100 000km as the service (replacement) interval for heated O2 sensors.
Tools needed:
New Bosch O2 sensor, part number 0 258 007 090/091, Audi part number 06B 906 265 D
22mm O2 sensor socket or wrench
1/4” ratchet or driver with 7mm socket
Philips screw driver
Cable cutters
Zip ties
The first thing to do is locate the O2 sensor. It sits on top of the cat, just behind the turbo on the left side of the engine. Use the O2 sensor socket to unscrew the old sensor. I had to make my own tool for this since the socket I got wouldn't fit over the sensor. I cute the socket in half and welded the 3/8” drive end to the side of the socket. You can buy the correct key for this though, I believe ECS sells them.
Follow the wire to the back of the engine and notice it's held on by 3 zip ties and 1 re-usable clip just below the connector. Clip the zip-ties to free the wire. I found it easiest to remove the breather hose from the back of the valve cover to give me a bit more room to work in. This is where you'll need the 7mm socket for the jubilee clips.
Detach the coolant reservoir by unscrewing the philips screw it's attached with and lifting it off from the back attachments. Set the reservoir a side and find the black O2 sensor connector on the firewall. It has 5 wires running to it. Pop the connector out from it's attachment by twisting it clockwise, then insert a flat blade screw driver into the slot on the side and lift to free the connector (similar to the headlight connector). Pull the connector apart.
Make sure the new O2 sensor threaded is lubed with copper paste or grey high temp lithium grease and screw it in. Then route the wire from the back of the engine to the connector and secure it to the ECU wiring harness with zip-ties. Reattach the coolant reservoir and make sure everything is in place and no tools have been left in the engine bay.
Start the engine and take the car for a test drive to raise the engine temp to normal. Everything should be working nicely and the engine feel quite a bit smoother. I replaced by O2 sensor at 200 000km, but it sure feels like it should have been done a long time ago!
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Originally Posted by catriple
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