Fan/RPM issue

Have a International at the shop with a DDEC 4 computer. When you crank the truck it high idles at 900 RPM to start with and the engine fan is off. When the truck warms up the idle goes to 600 RPM and the fan comes on and stays on until you turn the truck off. As soon as you re crank the truck it goes right back to 900 RPM and the fan is off.

Any thoughts?

 

Fan solenoid works properly and the fan clutch is a Kit Masters unit (Kysor) and is brand new. I repaired one small leak today on the fan but has no effect on RPM issues.

The A/C is not on.

 

Thanks. Will hook up this morning and see what pops up. Guy came in late yesterday and I didn't have time to look at it that much (none at all really).

Just thought it was odd how when the RPM drops the fan comes on. I would think if it was a/c switch it would be on no matter what RPM. I was leaning towards a temperature switch or an ECM issue. The ECM on the truck is a unit he put on several years ago that he says has been fine. He has his original that he replaced that he says there is nothing wrong with. This is a new customer and I don't "feel" like I am getting a true or complete story on his truck issues.

 

I think I may have found it. Hooked Nexiq up this morning and got a oil temp sensor fault. Sensor is reading -33. I then found an older post talking about this issue on the forum. http://www.thetruckersreport.com/tr...elers/157426-major-code-prob-w-detroit-3.html

I will let you know what I come up with.

 

4.9 volts at turbo boost sensor and 8.2 at oil temp sensor.. ECM issue or try a oil temp sensor?