Zedn Pull the crank sensor and check the pin wheel for movement and being tight on the crank shaft. They had some wheel come loose. What year is the motor and ECU? P0315 is a relearn of crankshaft position. Motor ran you said. Power to injectors all. ECu uses drivers to pull the ground and pulse them. How lng was this car without battery power? It could have lost the programming. Have you tryed to reload it? If you clear the code, does it come right back on? Hey GAV you seam to be the GM answer man, help the guy fix it.
Rick L. Ps are you still running a MAF sesnor? Did you have p807 before this started? Clutch position sensor would need to see wiring and to who the signal goes to. With seeing the wiring would think that is would control the starter from cranking or fuel and igniton from firing up the motor no spark or fuel. if you have above 20 psi of fuel pressure the motor will try and start. The plugs should be wet.