Engine engine speed/tachometer, but CKP signal is working fine

[JoeBean]

Hi all,

I've got a 2015 Sierra 5.3 with a weird issue.  We replaced the engine, and when we went to start it to re-learn the CKP it's hard to start and idle is really rough, and when it does start the tachometer/engine speed signal isn't working, so we can't start the re-learn.

 

I hooked up the scantool and we have crankshaft speed signal (I don't think it'd start if it didn't, would it?) and camshaft speed signal, but engine speed shows just 0 RPM.  New CKP made no difference.

 

Has anyone else seen this?  I'm assuming it's probably some weird harness/communication issue, but I just wanted to see if anyone's seen this.  

 

Only stored code is P0335 - CKP circuit.