autojoe wrote: Why need 3 crank sensors?
Because GM! :silly:
It's been awhile since I went to war with one of these. The way I remember it, the 7X signal is an variable reluctance sensor, the one in the block. Reports directly to the ICM.
24X is a Hall effect sensor at the balancer. 24 pulses. Also reports to the ICM.
3X is a synthetic signal generated by the ICM and sent to the PCM based largely off the 7X... I think? Like I said, it's been awhile. :blush:
As far as I know, the 3.4L doesn't have the dual sensor setup at the balancer. That's the 3.8L. 7X is for spark control, 24X is for idle stability. I can't say which sensor corresponds with your P0336. BUT, because the engine runs well, I'd suspect the 24X first.
This SD video may also be of value. Different fault code, but the ignition system is the same.