In 1996, Ford made what was probably one of the most controversial changes it had ever made to the Mustang. Since the day it debuted, the word "Mustang" had been all but synonymous with "Windsor small-block." But the times, they had changed -- the Windsor was out, and the high-tech Modular took its place.
The technical description for this code is "Lack of heated oxygen sensor switch, lean bank two." What that means is that either the oxygen sensor has failed and it isn't sending a signal to the computer, or the engine is running lean on the driver-side cylinder bank. If this code occurs by itself, it will usually indicate a bad sensor, a bad or dirty fuel injector or a problem in the electrical system. If it occurs in conjunction with a "lean" code for the other oxygen sensor, it's more likely low fuel pressure, a damaged fuel pump or pressure regulator, a dirty or defective mass airflow sensor, a vacuum leak or an emissions control system failure.