PCM not sending 12v to crank sensor

[Brownman863]

Working on a ups truck with a 2014 gm 6.0 with a E78 PCM ,no power ,backfiring into intake on acceleration,codes p0174 and p0171,while testing found that the PCM is not sending 12v to the crank sensor.replaced PCM and same problem,I'm testing at the PCM so I'm assuming the wiring to the sensor is good,I can jump 12v to the sensor and the fuel trims zero out .the funny thing is that the PCM puts out a steady 5v to the sensor not 9 not 4 but 5v?any ideas

[tbarn]

GM sensors almost always run on 5v. I may even go out on a limb and say they all run at 5v. P0171 and 174 are lean codes and that would be further evidenced by the backfiring. not sure what you have going on but check the fuel pressure.

Edited October 31, 2016 by tbarn

[Brownman863]

Tested fuel pressure and vacuum leaks,all ok ,o2 sensors have been replaced also , the injector pwm is at 3.1 at idle and should be around .9 according to a good running sister truck

[Brownman863]

Rechecked crank sensor trouble shooting,it has a three wire Hall effect sensor .12v from pcm,ground from inside pcm and crank signal fed to pcm.is this correct?

[Brownman863]

I apologize,talked to a freighliner rep today ,told me the same on the 5v reference,told me to check the evap line and purge valve that it probley has a big vac leak .thanks for the response will let you know what I find