99 saabwon't start

My daughter has a 1999 Saab 9.3 turbo which had been running fine. It suddenly would crank but not start. Not even try to start. Towed it to the mechanic. The next day it started and ran fine. Took it home ran good for two days. Now it's back to not starting. The mechanic said it had no stored fault codes and started everytime for him. We are towing it back to the garage today. It has a good battery and had a whole new ignition module a year ago. Any ideas? It has right at 100,000 miles on it.

Crank Sensor?

Thanks for the reply, I will check it out.

Finally got Saab fixed. The mechanic found that the main relay was only switching partial voltage and that the fuel pump was on the verge of failing. He thinks maybe the low voltage condition was a factor in the fuel pump failing. Replaced relay and fuel pump. Car seems to be fine now but we will see.

make sure to check the wires at the back of the main relay. i have seen this problem sneak up a few times. the wire terminals back out of the relay but make intermittent contact. hard to diagnose.