is this concerning the cat ?
 

P0420 Catalyst System Efficiency Below Threshold. thats what showed up when my nephew pluged his scanner. he also told me that the ecu was giving a code 67. Thanks in advance

Re: is this concerning the cat ? (BeesDA6)
 

Both codes mean the same thing. It could be the cat or it could be the 2nd O2 sensor (after the cat). That 2nd O2 sensor is how the ECU measures whether the cat is working.