P0420 and P0430 on you Jaguar X-type

P0420 and P0430 on you X-type means that the computer sees something wrong with your oxygen sensor readings. P0420 is for bank 1 which is the bank towards the back of the car and P0430 is bank two which is much easier bank at the front of the car. There are two oxygen sensors per catalytic converter and two catalytic converters so you have a total of four oxygen sensors. The computer compares the upstream oxygen sensor (before the catalytic converter) signal with the downstream oxygen sensor (after the catalytic converter) signal to make sure the cat is doing what is supposed to be doing, reducing emissions. So these are the possible causes:

Most likely (in this order):

• Bad upstream oxygen sensor: Denso 234-9029
• Bad downstream oxygen sensor: Denso 234-4798
• Bad catalytic converter

Not likely but possible:

• Bad wire between the computer and the sensors
• Bad computer

So what do you do? If you haven't replaced the oxygen sensors already I would do that first, because they do go bad and new sensors show small improvements in fuel economy. I would change them first try the upstream (because is closer to the engine and works harder), then the downstream.If that doesn't work you might want to try and exhaust shop because the Jaguar original cat is really expensive.