So I have a 2000 ML320 and I got it with a check engine light. After working on the car, I am down to my last two codes, both are heater circuit problems in the post-cat oxygen sensors. After inspecting the plugs I noticed a lot of corrosion which all led me to new sensors wired directly to the car bypassing the original connector in the car which was too corroded to fix. Now, with fresh wiring i noticed on either side, the heater wires (the two thicker ones) one seems to have steady current while the other blinks on and off. I'm assuming this is why the sensor doesn't heat up because the power keeps getting cut off every second or so? If not please let me know as I am out of ideas and I've spend about a week trying to solve this! Thanks.