hi
i went to the garage to change my front pipe
100 km after the reparation the oxygen sensor had problem?

what do you think?

i have a mazda protege5 2003 with 76 000 km

is it normal to change the oxygen sensor? or maybe was it damage by the remplacement of the pipe?

For the future, when i have the light on (check engin) how can i find myself the problem?

thanks by advance