I have a 2002 Zafira 1.6 16V which has the fault code P0136. I changed the 2nd lambda sensor and erased the codes. Next day the same code came back. What can I check next? I tried Cataclean to clean out the cat and fuel system, used Shell V+ in case it was supermarket petrol. Do I get another sensor in case the one I fitted was faulty? Any help would be appreciated.