Savage86

I recently bought a 2000 ml430. Trying to get it to pass inspection. Things I've replaced. All 4 o2s, maf, air filter, plugs, wires, and cats. My problem is when clearing out the o2s codes after driving about 50 miles with scan tool still hooked up there are pending codes for all the o2s again and once vehicle is shut off and restarted my check engine light comes back on. I had to hard wire the O2 sensor that's under carpet on drivers side because plug was severely corroded due to leak. I just would like some advice on where to turn too now. I've replaced everything I can imagine and yet codes keep coming back only for the o2s.....

CafeRacer87

Take a step back and look at the big picture: What exact codes do you have for O2 sensors?


The reason I ask is because there are 20+ codes for O2 sensors, from slow cycling to open faults, etc etc. Just because the code has the word "O2" in it does not mean the sensors are bad.


The computer is programmed to look at data from the O2 sensors and react accordingly. For instance, if your intake manifold has a leak, the O2 sensors will see the extra air (which is entering the engine AFTER the mass air flow) and think that the engine is running LEAN, and dump in more fuel as a result.


So what codes do you have?

Maj. Dundee

The reason why your CEL comes on after a restart is that mostly all codes will set after a two trip cycle, except misfires will will set immediately.

I don't know how you hard wired, soldered, twist & tape or crimp connected, but if at any point, one or all of the copper wires were not bright, you will not get accurate readings on those wires going the the ECM.

Below is a photo of the right rear wiring harness under the rug going to the ECM.