P2099 Code
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Joined: Sep 2022
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2011 S550 4matic
P2099 Code
So I've been getting check engine light at times, other times it goes away. Most recent code was p2099 but I was watching short term fuel trims, they were somewhat erratic jumping around up and down. Checked for vacuum leaks, nothing apparent. I have changed the vacuum check valve on the driver's side rear valve cover and check valve appears to be working correctly. What I did see that appeared a bit strange is that scanner tells me that downstream catalytic temps should be 750+ and mine are lower, 650ish. Does anyone think I need o2 sensors? Maybe something else?
Thread Starter
Junior Member
Joined: Sep 2022
Posts: 72
Likes: 31
2011 S550 4matic
So as quick update, not sure if it's soon enough to mean anything. I had found one issue, the drivers side air boot clamp between the air filter and metal duct was not seated properly. I did fix that yesterday when I was doing a smoke test and just generally checking everything. Immediately after fixing it and erasing the code, fuel trims still erratic but today after a few hours of driving - all lm monitors completed and fuel trims steady between 0 and 1, car is running perfectly and no codes. Time will tell if it really is okay. I think maybe ecm needs some time to "normalize" after a repair.
Thread Starter
Junior Member
Joined: Sep 2022
Posts: 72
Likes: 31
2011 S550 4matic
So light came back again, this time something about bank 2 too rich downstream of catalytic converter. I dropped both cats and replaced all 4 oxygen sensors, oem Bosch. With 130k miles, should be done. Boy the sensors not easy to do on these, impossible to do without removing exhaust pipes and need to lower transmission to get to sensor plugs on drivers side. All done now, I drove it a bit, 7 of the 8 monitors completed, fuel trims seemed stable but time will tell if this comes back again. Next step if the codes come back will be to send out fuel injectors for cleaning/testing to make sure I don't have a leaker.
Thread Starter
Junior Member
Joined: Sep 2022
Posts: 72
Likes: 31
2011 S550 4matic
So after driving a couple of days with new O2 sensors, all lm monitors are now functional and fuel trims are remaining normal- more or less 0 to 1 or -1, looks good so far but I'm skeptical, waiting to see what happens in the next month or so
