Odometer 205,000km Cat. less than a year old. Down stream O2 sensor 1 year old. Added 1 cup methyl hydrate to a full tank of gas Week later, tank almost empty, i'm getting the code P0420. Would adding the methyl hydrate cause the code? Thanks
It's gas line antifreeze. Just added it into the tank.
If you just added what's recommended then it probably won't affect the P0420. However, if a greater amount was added, then yes. Adding oxygenates to the fuel will cause the engine to run lean (alcohol=oxygen). An engine that runs lean over a long period of time can DEFINITELY kill a cat.
Why did you add methanol to your fuel? It's never a good idea to add anything to your fuel that isn't recommended by the maufacturer. What fuel did you add the methanol to? Was it ethanol? Is the vehicle designed to run oxygenates in the fuel?