How to O2 Sensor 1999 Mercedes S420 W140

[@timotheussanders6485]

Did the check engine come back on once you change the o2sensor? I change mines and two day later the light came back on. But the car still drive fine I got it up to 128mph on the Highway no Problem. Any information you can give me would help

[@MileHighDreamz]

No it did not. If you're still having a code I suggest Google search the code and it gives you a list of reasons. Could be an exhaust or intake leak if I head to guess. That or you used an aftermarket sensor

[@urmaswu6203]

Hi.I have w140 S320 96y and O² sensor wont work correctly, its ON few sec and then its shut down/OFF Do i need to replace O² sensor? No check engine light. There is many different sensors in the market, witch one i need do buy?

[@MileHighDreamz]

Is the O2 sensor is on then shuts off, or the engine is on and then shuts off? I always use Original Equipment Supplier for O2 sensors. The aftermarket ones will give Mercedes problems. You don’t have to buy from Mercedes, just look up the brand and model number. For example, if it’s a Bosch brand, then you buy the same Bosch model expect it doesn’t say Mercedes. Check around for an intake leak and make sure you have fuel pressure and ignition

[@urmaswu6203]

@@MileHighDreamz At the inspection, mashine show that O² sensor turn off when engine running

[@MileHighDreamz]

@@urmaswu6203 which sensor is it? Number one or two? If it’s number 2 (downstream) then it doesn’t affect your problem. If it’s number 1 (upstream) then change it and see

[@urmaswu6203]

@@MileHighDreamz There is only one sensor before calisator upstream

[@MileHighDreamz]

@@urmaswu6203 if there is only one and it is upstream of the catalytic converter then I would change it and see

[@marekk3399]

I have a code for bank 2 sensor 2 on my 97 s420 and I think if there is a check engine light on then the engine doesn't use the varrible valve timing so performance is worse if any sensor is bad.

[@MileHighDreamz]

You say "think". Could you pelase verify that this car does that with any check engine light, or where you got the info from? Asking for my own knowledge. Seems kinda of ridiculous for a sensor 2 to cause limp mode/limited performance by ecu. All it does is measure the efficiency of the catalytic converter.

[@marekk3399]

@@MileHighDreamz Sorry I tried to find the place I read it. But I can't find it now. I did alot of reading about the m119 engine when I worked on the timing chain. And I read this info then. Since the repairs I've had not Check engine lights and I can feel the car runs much better and better fuel economy and performance. Good luck to you.