THE DIAGNOSIS OF FRONT AND REAR OXYGEN SENSORS CAN PROVE DIFFICULT SINCE THE OPERATION OF THE REAR SENSOR CAN INFLUENCE THE OPERATION OF THE FRONT SENSOR. THE SENSORS SHARE COMMON SOURCES OF POTENTIAL FAULTS BUT ALSO HAVE UNIQUE FAULT SOURCES THAT MAY TRIGGER DIAGNOSTIC TROUBLE CODE (DTC) ENGINE CONTROL MODULE (ECM) 28 OR 29. *TT