Expert: Mike Evans - 2/15/2010

Question
My car cuts off.  I took it to get a diagnostic reading and the code read P0171 lean bank 1 what does this code means? I have a  
pointiac 2002 grand am, with a v6 engine.

Answer
    It means that either the oxygen sensor in that bank is defective or you have a bad fuel injector on that bank.  Because you are having a problem with the car cutting off, I would suspect the injector first.  Try removing the spark plugs, one by one, in that bank and looking at the electrodes.  A healthy mixture will give a light brown or tan color to the center insulator.  If it is running too lean the insulator will look white (as though new).  Too rich and you get black or very dark brown with little crunchy sooty deposits.  If one cylinder is showing much leaner than the others, try switching that injector with one of the others.  Run it for a while (several days) and check again.  If the problem moves to the cylinder with the same injector, then that injector needs to be replaced.  Since all of the injectors are the same age, it might not be a bad idea to swap them all out.  If all of the plugs look the same, then the Oxygen sensor is probably bad on that bank.  Since they don't cost much, you should replace both of them.