Hi,
About 6 month ago, my check engine light came on and the mechanic told me that my front right oxygen sensor went bad and needs to be replaced.
Front right oxygen sensor was replaced with brand new part and check engine remained off for few weeks.
However, check engine light came back and I took the car back to the mechanic. I was told that MB computer is being too sensitive and there is nothing to worry about.
He said the check engine light will go out after few restarted. Indeed, check engine light disappeared after few days but it would come back after few days as well. It just keeps repeating this cycle but I'm trying to get that fixed.
I've asked around and I got various feedbacks.

1. Start using 87 gasoline which would produce less carbon.
2. Replace the old oxygen sensor(one on the left) with a new one since data from the oxygen sensor on the right(one that was replaced 6 month ago) and old one on the left doesn't correlate with each other.
3. Replace both left and right oxygen sensor since readings from the sensors are very sensitive and slight usage can create difference in readings.

Please help. Small mechanical problems on this car has been costing me too much money ever since the warranty expired and I don't want to spend another $350 for oxygen sensor job.

 

How many miles since your last tune up? Are you having a dealer or service shop work on the problem?

 

I have little over 70K right now and I got full tune up done at the dealer at 30K. I stopped taking my car to dealer when it hit about 50K.

 

I hate to endorse a dealership, but w/ both my MB's I have found that I actually save in the long run with them. Your tune up should give you 50K miles but it sounds like you may need either 1) new plugs or 2) reprograming of your main computer. If your o2 sensor was truly bad I doubt you would have these symptoms, I have noticed both of my cars will pop the engine light when I have a bad plug and boosting the octane will cause the light to go off. My SL however was also showing symptoms under cold start and stop and start driving. It needed reprograming ($60) which was much better then the $250 for new plugs on my Kompressor!

Good Luck!

 

87 octane gasoline produces less carbon and thus use it in lieu of 91.

Not only is that statement wrong, but it is also dangerous. Whoever said that should be hung.

Cars that are programmed for Premium Gasoline (91 Octane) will knock or ping when 87 is fed. You keep doing that and expensive valve-job will follow.

 

Take a latest OBDII reading while your Check Engine light is ON. (Ask your mechanic.)

Tell us what it says, exact error codes. Don't let the hobo mechanic interpret them for you.