I have a 97 thunderbird 3.8 with about 25 thousand miles on it. The check engine light is on.I had it check an was told I need 4 new 02 sensors.there are 4 cats. Would all 4 go bad at once or is there another problem. I was told That there could be another problem but till I solve this one they can,t tell if there is. Do I really need 4 new o2 sensors or is there just one bad one? Or is it electrical?