Oxygen sensor problem

check the wiring for the first Oxygen sensor and the sensor itself. I think your vehicle has two, one before the cat. conv. and one after the cat. conv.

good luck, dave

Hi Dave! There is only one O2 sensor. I checked the wiring but I'm not sure how to check the sensor... Is there a simple way to find out if the sensor is working properly? Thanks!

what year is this A4? You should be able to hook up a vag-com tool (ross-tech.com) and easily tell if the 02 sensor is working. Also some use a digital voltmeter/multimeter and check for voltage at the 02 wiring plug with the plug still connected (backprobe). Voltage has to fluctuate. Bentley repair manuals might tell how to do this. Or searches on the web will give you sites like these:

Your 02 sensor should be heated also, and that may cause other problems if somehow the wires are shorted/melted. :-(

later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris

Hi! It's 1996. I hooked up vag-com to it but I don't have the correct label file for my engine, so I'm not sure if I'm looking at the correct measuring block. I shows a value of around 0.5 V and it fluctuaes... It drops to 0.0 then comes back to 0.5 and so on... BTW I was also looking at another measuring block that is showing four voltages. These voltages are not the same, and they change as the RPM change, but when I rev up the engine to about 4000 RPM they equilaze and stop at

5.100 V. Do you know what this could be?

Thanks again for your time!

Cheers!

Hi! I forgot to mention one thing earlier... When the engine is cold it idles at aprox. 1200 - 1300 RPM. After about two minutes it drops to about 860 RPM. Is this nomal or should it be idling at 860 right away? Thanks!

Did you introduce a vacuum leak, like the tests in those websites, to see how the values change?

Also you may have to make sure any grounds are clean and tight. I have seen some earlier VWs and Audis with bad grounds that stopped the 02 sensor from functioning.

I am not sure but 5.100 V does not sound right, but are you checking this with the vehicle in motion? I am also not sure of your FI system either! 8^) IIRC In the USA, most 1996 vehicles have OBD-II with 2 Oxygen Sensors sensors.

later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris