Funkwagen

I'm beginning to think it's time to replace my O2 sensors, at least the downstream, post catalytic converter sensors. I'm just at 140,000km now and I've noticed that it seems to take the O2 sensors longer than usual to detect changes in oxygen levels. Logging data with Torque and an OBD connection, the sensors don't change voltage from ~0.7V even when the engine runs a lean air/fuel mixture while coasting/at low engine load. I've been having issues with a rougher than normal idle, and abnormal engine timing adjustments. Makes the car sound like it's being run on less than optimal fuel grades (which it never has since I've owned it) and feels like it has less power than it should.

What's the average useful lifespan of the O2 sensors in this car? If people have replaced them, at what mileage were they replaced? Would failing/old/"lazy" O2 sensors cause subpar engine timing adjustments and the rough idle? Also, I imagine frequent "spirited" driving would cause the sensors to wear out faster than normal, unless I'm mistaken

michail71

I'm not sure but it will be interesting to see what your results are if you change the sensor.

Could it also be related to carbon buildup? I think that can cause timing to pull back. I haven't heard much about carbon buildup in any of the Mercedes direct injection engines but that seems to be a common topic on BMW and Audi groups.

Funkwagen

Thought about carbon buildup, but I think it's more to do with the sensors. Logged some data with a histogram for the voltage of the O2 sensors, the first one was logged when the car was running poorly, slower acceleration, rougher idle, etc. The second one was taken when the car seemed to be running "well", smoother idle, etc. It's sort of concerning that the O2 sensors never read below 0.7v in the first one.. so I guess that might be my answer. There wasn't a difference in driving between the two, other than the fact that the second one was taken later in the day after the car had been driven about 110km, some with some highway. Both screenshots are after 5 min of logging data, driving around the city. To date there have been no fault codes related to this (or any at all)

Is there anything else that could also cause this?




Malfunctioning?




Normal?

michail71

I'm not sure about with this car but fault codes don't always trigger before an observant driver picks up on things.

What OBD reader are you using for Torque? I've been thinking of getting one.

Kent Seaton

I use the Veepeak Mini. It's a generic one like all the other made-in-china ones, but it works well. If you use Android, save yourself some cash and just go with the BlueTooth option.

cetialpha5

I've replaced O2 sensors in other cars and the consensus was that you always replace the upstream sensors, but not the downstream ones. It's the upstream ones that usually do all the work as they switch all the time, when the downstream ones go, that usually means the cats are bad as the downstream ones typically don't really do much.