Mercedes 430 Oxygen Sensor? - PB
I have a 3year old 42k mile ML430. I've had it a couple of weeks and the fuel consumption is worse than my previous ML430 (i.e. terrible). It smells like it is running rich all the time and even when fully warmed up the exhaust still smells 'rich' and slighly smoky. I am guessing something could be wrong with the oxygen sensor or the connections. Has anyone had anything similar? And anyone know of a MB specialist near Windsor, rather than get the MB garage to do it?
Mercedes 430 Oxygen Sensor? - Kevin

Take it for an MOT test.

Much cheaper than going to a dealer and the emmissions test will confirm whether the cats, lambda sensor and ECU are working correctly.

Mercedes 430 Oxygen Sensor? - Cliff Pope
Will it? I thought the MOT emissions test just said pass or fail - I don't think they do a full diognostic test and tell you whether it is the Oxygen sensor, Catalyst, etc at fault.
I'd say go to a specialist tune-up operator and spend £50 or whatever having the whole system looked at.
Mercedes 430 Oxygen Sensor? - RichardW
Heavy fuel consumption and rich running are probably signs that the coolant temperature sensor has failed, and the car is effectively running with the choke on all the time. As the ECU is not seeing this as a fault - it just thinks the engine is cold all the time - it doesn't put the warning light on. You need to get the resistance of the sensor checked, and an injection specialist is the place to go, so you don't have to remove your arm and hand it over at the MB garage.....

Is it illogical? It must be Citroen....
Mercedes 430 Oxygen Sensor? - Peter D
If the ECu light is not on I suspect you have a faulty temperature sensor that ifs fooling the system into running in partially choked mode thus the smell and fuel without a fault light as the sensor is higher in resistanc ethan it should be but not open cct. It could just be a the connection to the sensor that has corroded. A good tune up shop will soon find it. When you say smokey, what colour smoke, white for oil grey for fuel. Regards Peter
Mercedes 430 Oxygen Sensor? - Peter D
Part two. Yes it could be the O2 sensor that is lazy i.e. very slow cyling thus leaving you with a rich mixture and no fault light. Get it check out as the Cat is having to deal with too much unused fuel. Peter
Mercedes 430 Oxygen Sensor? - PB
Thanks for the feedback; I'm taking it into the local specialist in the morning to see what he thinks and I'll let you know what the problem is.
Mercedes 430 Oxygen Sensor? - PB
It was the Oxygen sensor. Had to go to the MB garage in the end who seemed to spend a long time testing everything. I don't know if that was strictly necessary as apparently the ECU did show the sensor fault. Hefty bill unfortunately.
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