Swartlik is right I had one done on my old blazer. After replacing the cam the parts were shall we say too new and the computer wasn't sensing the wear it had the previous day so it wigged out a little and through a code. However the truck ran fine but I had this case re learn done anyways because I was told bad things would happen if I didn't. Shop charged me $55 and sent me home no light and truck ran a little bit better

 

On the way home from Work I stopped at a dealer.
I told them That I changed the Cam and the Timing Chain and obviously the Distributor was out.
The car is running fine other then the code. I told the service manager that it has this P1345 code and all is well but it need s Relearn. He said they charge an hours labor for that. So that would be $114. Yup , that's what they get here In the shameless State called New York.
On Saturday I went to my friends shops armed with all the info I got here. Plugged in the OBD2 scanner...The distributor was in 22 retarded, pulled it, shifted it back one tooth.. it was 23 advanced. 4 hours later we could not get the Timing at 0 degrees.. We guessed it was because the new Cam may have not had the Distributor gear teeth perfect with the Lobes of the Cam. The Cam was probably designed for a Chevy that had a Rotating Distributor, not one Locked in by the Holder like these are.
So we had it at 22 degrees retarded, Through the Distributor Holder in the garbage, Bolted down one from an '85 Small block Chevy and rotated the Distributor until the scanner read 0 degrees....Should have done that 4 hours earlier.
No code.
I cannot see me letting someone Run the snot out of the engine to do this Relearn. 5100 RPM? whew!

P.S. What idiot decided a Plastic distributor was a good idea????? I saw that and almost died. Apparently the mechanics can't seem to prevent the Hold down holes for the Distr Cap from cracking after the car is a few years old.. no matter how gentle they are. Tie wraps are their friends from what I hear. Just another straw in GM's Back.

 

Hopefully that works for you, but I doubt it will last long. The PCM controls timing and does not need an adjustment. My dealer (Bill Cram Chevrolet) charges $60 for this procedure... New York as well.

And about the plastic distributor body. Manufacturers had been doing this for years. It actually works very well if people pay attention to what they are doing when installing the screws. Gone are the days of meat fisted mechanics that just tighten things until they are tired.

 

Yes teh PCM controls teh timing. But I believe The P1345 code pops up when the Mechanical Settings are beyond +/-2 degrees. So althought the PCM made teh car run fine, teh fact that mechanically the Distributor was not right at TDC with teh Crank, was cause to give me a code..

With the Heat and cooling that is found under the hood. Plastic might be ok if you keep a car two years. But Aside from this Blazer. My newest car is a '91. Plastic and Longevity do not go hand in hand. I feel the way with the pitiful Plastic Intake Manifolds on many cars. They are Light, and cheap and fine until you need to actually touch them to do maintenance. Like Plastic Tanks on Radiators. All good for teh warranty period but if you hold onto your cars for 20-30 years, they are junk