hey guys
i have 2008 gl450 x164 a month ago i changed O2 sensors both banks after changing it runs well but again the same codes appear again (using mid grade fuel) is it the problem with fuel or its cat converter?
plz help

 

All the system is telling you is that there is too much oxygen in the exhaust post cat. It's assuming this is because the cat is not doing its job. It could be other parts of the fuel system.

If you haven't already, I'd change the MAF sensor and, if you can get to them, the upstream oxy sensors.

The cats do wear out, sometimes earlier, sometimes later. How many miles?

It's probably not the fuel. I've burned regular in my 07 for 120k miles now.

 

hi
thanks eric very kind of u miles168 and i never cleaned or changed MAF oxy sensors were changed (after cat) what do u think what should be done ?
thanks & regard

 

Given you have the errors on both sides, I'd change a part that affects both sides first: MAF sensor. They aren't very expensive. Take your time on reassembly so everything goes together comfortably. There is very little holding the sensor in place.

If you live in a state that allows aftermarket cats, then weigh the cost of cats versus the upstream sensors, which are both more expensive to buy and to install. Here in California, I would first do the downstream sensors, then the MAF sensor, then the upstream sensors, then the cats.