Question

P0420 - this code and check tire pressure are in my 2003 Chevrolet Impala help, please

Answer 1

P0420 means the catalytic converter on bank 1 is or has failed and is no longer working like it should.

As for the tire pressure light, this is likely caused by a bad sensor in the wheel. Also, if the tires have been changed, the sensors have to be activated. If not, on some models you can see the tire pressure as it's reported to the computer and it will show no pressure.