Help i have replaced o2 sensors and i am still getting this code p0420. Bank 1. Does this mean drivers side cat is bad or should i try another sensor
Yes. Your computer takes readings from the sensor before the cat (S1) and compares it to the sensor readings after the cat (S2). If the cat isn't doing it's job, you will get that code.
You can diagnose this fairly easily if you have access to a scan tool and know what to look for. Readings will be too close to the same between B1 S1 & B1 S2 o2 sensors. ST & LT fuel trims on B1 will likely be in the high negatives as well if the cat is bad and your o2 sensors are working properly because the computer will be trying to lean the mixture out to reduce emissions. Compare those to B2 values since they are in spec, if you don't have actual specs. Hope this helps.
