OK, I just meant it's really nothing more than a little heating coil and it will have some random probability of failing at any time (like a light bulb). They are very easy to diagnose/fix on a 616/617. You can usually feel when one is gone by the slightly rough start. I've always been able to identify the bad one with a multi-meter from the relay plug. If you have small enough hands and don't remove the injector lines, changing on GP is very quick (remove the nut and don't drop it, loosen the GP with a small wrench, spin it out with your fingers and replace). It's the kind if thing I will stop and do if I happen to notice one is out when I'm leaving home (if I have 5 extra minutes and I don't want to have to wait for the engine to cool off later).