No RPM reading in scanner

[amrg]

My tach works fine. But when I have the obd scanner connected I cant get any readings, just 0 RPM. Tried hptuners and same thing.
I need the RPM signal from the pcm to do tuning on my truck. Anybody knows what sensor is responsible?
Also is the tach sensor different from what the pcm reads?

 

[alrock]

Don't know. My scanner works fine - cheap OBD scanner from eBay with Torque Pro on Android.

 

[f5moab]

PCM sends the rpm signal (as well as many other readings) to the IP gauge via the serial date link. It should be as accurate as the gauge is showing. The weak spot is the actual gauge might be off a bit (like the temp gauges is often not totally accurate).
The signal you are getting from the OBD II connector under the dash (where the scanners plug in) is also supplied via the same serial data link.

 

[amrg]

Is it possible that the tach reads a different signal than the one pulled from the pcm? My Tach works fine but its the obd2 reading I cant get.

I read on ls1tech on certain vehicles the IP tach gets its reading from the CAM sensor while the pcm displays the CRANK sensor.

I had the RPM values showing before doing my trans rebuild. After the rebuild first thing I noticed was the OBD scanner giving me 0 for the RPMs.

 

[f5moab]

NO. As stated, the PCM receives the rpm and passes it along, via the serial data link to the gauges. It is a two way wire, messages are received and sent via the data link. But the gauge may not display the same RPM as the PCM has due to the gauge is not being accurate. But usually only off a hundred (+/-).