Cat 262c no crank no start

[DslDrew27]

MST04756
Current hours 4450
No crank no start.
Active code 190-8 engine speed sensor. Key on-the monitor screen is reading 7281 rpms. Also seem to have a low voltage issue. Battery is reading 12.3 but the monitor is reading 11.5
I’m really confused/frustrated. So far I’ve confirmed that the seat switch and the lap bar switch are working, have to double check the door switch. What other conditions have to be met for the ecu to permit the engine to start? Also worth mentioning that during my troubleshooting yesterday with the key on for a bit, the alternator was getting warm.

I’m really trying to stay with basics stuff like the seat switch but this active code for the engine speed sensor and the fact that the monitor is not reading 0 rpms is throwing me off.

I do have a schematic and a service book, however this is the first time I’ve seen a Cat wiring diagram. Kind of hard to understand. I’ve looked at and can understand Komatsu diagrams fairly well.
Any advice would be appreciated.
Thanks
Andrew

 

[Mark250]

hi ,your alternator should not be getting hot ,as a first step I would disconnect and isolate your alternator from the machine and see what happens
mark

 

[DslDrew27]

i unplugged the alternator, and turned the key on, monitor said 0 RPM, gave the key a quick bump and she turned over. new aftermarket alternator for $185 versus a 249 reman from cat. She fired right up and voltage was at 14.2.

totally forgot about that R terminal on the alternator, a while back i was troubleshooting the charging system on our Komatsu pc300, that wire goes all over the machine.