2007 Series 60 fan clutch quit working

Need Help trouble shooting cooling fan. Fan clutch stays engaged all the time making me loose fuel mileage. I have good air pressure no leaks. Manually tested clutch function on the fan by blowing air into line going to the clutch works ok. Checked control valve manually by applying 12 volts to solenoid and works ok. Checked voltage at fan solenoid connector zero (0) volts. Checked fan fuse and is ok reads 12 volts both legs. Checked AC high pressure switch and reads ok switch is closed also checked the connector to the AC switch. Unplugged the fan control valve solenoid connector checked for voltage and got nothing at first then about 3 volts seconds later then a full 12 volts about 10 seconds after that. As soon as I plug it back in the voltage drops to zero again. I repeated this process several times with the same exact results. I started to run the wiring down looking for a bad or corroded connection but found none. I'm beginning to think the ECM is failing some how. Also there are no error codes showing up from the ECM.

Before I spend the big $$ I was wondering if any of you drivers could help. Much appreciated.

 

Thanks bunch. I'll dig into that and let ya know what I found.

But, I have to ask. If 12 volts comes from the fuse box why am I loosing the 12 volts?
I can understand the ground going to the ECM loosing connection but if it is doing that the 12volts to another ECM ground should not fade away.

 

That helps. Knowing the sequence of operation will help me understand what is happening.

 

Thanks a bunch MHYN. Just what I was looking for. I just might get this thing fixed. You guys are just great. I now have to find the time to tear into it.

 

No...I was measuring the voltage at the valve connector. I dismantled the male end of the plug to expose the wire pins.

No...I don't have access to a dddl.

It looks like I won't have time to investigate the problem till this weekend. With all the info provided in this thread, I should be able to fix it.