Nissan Repair: MIL Light, engine management components, vacuum leaks

Question
I'm a New York State resident..My truck won't pass inspection.  The MIL light keeps coming on.  The codes change, but everytime I replace a part some other code comes up.  I've changed the front O2 sensor 3 times, hoping I just got a bad O2 sensor, but the code reapears after about 8 miles of driving(PO130: Oxygen sensor-bank 1, sensor 1)  After changing the first O2 sensor, the code went from PO130 to some code that indicated the MAP/BARO switch selenoid valve.  That wasn't the problem either.  Po130 and P1105 apeared.  Changed the Map sensor, itself, but then the code switched back to Po130, so I changed the O2 sensor, AGAIN!  The code came back on after I drove about 6-8 miles.  I've been to multiple mechanics and none of the can figure it out.  My inspection has ran out over this issue and I need your help.  Please help!  Thank you, in advance!

Answer
Hi there, when a trouble code indicates that one of the engine management components malfunctions, e.g. the O2 sensor, it does not necessarily means that the sensor itself had failed. For example, a vacuum leak, can make the O2 sensor to send a signal of lean mixture to the ECM and the ECM tries to compensate by increasing the firing time of the fuel injectors. Of course that will not correct the problem and the ECM will continue to read a lean signal and the MIL will come on. So, we must always find out if there is something else that causes a sensor or an actuator to fail! We start by checking all wiring and vacuum lines that the ECM uses to communicate with all the components. We check for proper voltages, continuity, terminal connectors, broken or loose wires and in MAP/BARO case, the vacuum line connection. We test, BARO, TPS, O2 etc either with a multimeter or using a scanning tool. Battery voltage must not be lower than 12.6V. Vacuum leaks, if any, must be repaired. All in all, anything that could send a faulty signal to the ECM. If everything checks out normal and within specifications, we are looking at a problem with the ECM itself. Do not replace any parts at this point! An ASE certified tech in engine performance, can determine if the ECM has failed.
Hope this helps.