2006 buick rainier lh6 5.3 is always in 4cyl mode no lifer ticks not using oil got 45 lbs oil pressure at idle it's giving me codes for dod p3349, p3341, p3325 and p3301 and p0315 crank position sensor not learned and it won't start on the first crank I was told to change the oil pressure sensor but it's working fine I do have a new one

 

did you take it to a mechanic ?