I’m trying to pinpoint the exact source of the P0420. I hope someone here would think with me to solve this. Below I have briefly stated the background of the problem in bullet points. - Original cat. got stolen a year ago. - Bought aftermarket cat. & it worked/works just fine. - Hit a bump on the road a couple of months ago, a while later the P0420 appeared. perhaps appearing of this code and hitting of the bump were accidentally timed close to one another. - Used Liqui Moly cat. system cleaner sprayed through the throttle body. It didn’t solve the issue. However somehow damaged the MAF sensor. - Replaced the maf with new one. That’s cured maf related codes. STRANGELY, also removed the p0420 code. However, it appeared again a while later - Took out the cat. to visually inspect it. It didn’t look clogged at all, still cleaned it with diesel, detergent/water. - Still, no change! A/F (upstream) sensor: Using OBDLink scanner, it shows 0,00 volt. It doesn’t change at all. I can’t remember the number for its resistance. Oxygen sensor (downstream) at Idle 0,06 volt with +25% injection : ~ 0,06 volt with -12% injection : ~ 0,8 volt Resistance: 26 ohms. Can we condemn the two sensors, because of the odd numbers, to be culprit of P0420?