Crankshaft Position Sensors and Camshaft Position Sensors do not always throw codes or turn on the MIL, yet if they fail, your car will not run. I have truly appreciated my code reader. It has solved many issues. I highly recommend one in addition to your Haynes and dealer manual tests. And yes, the ASD relay can cause this exact problem, but so can many other items like the position sensors etc. Sometimes a code is present that does not illuminate the MIL as well.