Check engine - Oxygen Sensor 99 SL

[99SL5]

I have a 99 SL500 with 47k miles. Last weekend I filled up at a small town Mobil station. On the pump it said their gas is oxygenated. I am not sure if this has anything to do with my CEL coming on but I thought I would mention it. After using a quarter tank the CEL came on. The OBD code was P0150 (Oxygen sensor bank 2 sensor 1). It seems to be running fine. I have removed and retightened the gas cap with no luck. I erased the code. Is it safe to say that if the light does not come back on everything is OK? Should I replace the driver side O2 sensor before the manifold? Does anyone know how to do this? Is it difficult? Is it bad to drive the car with a bad sensor?

Thanks

[Kebowers]

If the light stays off-be happy.

Low mileage for it to fail. Complain to the gas company--contaminated gas can cause failure.

[99SL5]

The check engine light has reared it ugly head again. It stayed on for a couple of days and went out again. I have decided it probably needs replacing. I took it into the dealer because I thought it would be covered under the 8/80,000 mile emission warranty. The dealer pointed out the fine print in the warranty maual that excludes O2 sensors. I told him the ODB II codes indicate an 02 sensor failure on the drivers side before the CAT. He told me they would have to run there own diagnostics which cost $98. He called me a day later and said "there is an an 02 sensor failure before the CAT on the drivers side"......that will be $98 for the diagnostic and $450 for the repair. Am I way off in thinking that is crazy? The part is $100. Where is the other $350 going?

I would rather do it myself if it is not to difficult. Does anyone know where it is located? I read a post for a e420 that requires the tool in the picture. Will I need this? Some MB vehicles apparently need an ordinary 22mm socket.

[RickM]

Needin the tool depends on the replacement. If you go witrh a generic replacement form a place like Napa you may have to splice the wires together as opposed to using a connector. The special socket is designed to establish a decent grip wile the wire is attached to the sensor.

Here are the Bosch part numbers for the sensors:

You'll notice the OE type and Universal type. The Universal MAY be cheaper and without the specific connector.

[99SL5]

Does it say "2 required" because you should replace both pre cat sensors?

Are the sensore located just before the cat (under the car)?

Thanks again for the input. I would probably get the OE so I don't have to splice any wires. It will still be a lot cheaper than $450