voltage drop on the fan solenoid supply... causing the fan to stay on

been doing a lot of electrical tests with a friend here who has an 09 Pete 387 with the Cummins. We have insite and have been doing multiple resistance checks, voltage checks, sensor checks, ground checks, data monitoring and etc...

The issue is, there’s 12v power on the fan solenoid supply with the truck running. Then at 1500rpm the voltage drops to 9v, tested by using the power probe tool. This causes the engine to fan to run and if he’s going down the road it will stay on because t’s logging code 0245 fan circuit low voltage. Does anyone got any ideas on this one? We’ve already done the trouble shooting tree for the fault code, testing for internal short on the solenoid, short to ground, pin to pin short on the harness and etc. the solenoid did pretty much fail, testing right at/over 3ohms. He’s getting a new one tomorrow along with some more sensors.

Anybody got ideas or experience on this one?

Thanks

 

We did check the ECM power cable for resistance. Unplugged the ecm connector and the battery connection. Tested good. I didn’t watch the actual voltage while going up in rpm, except at the oem harness fan solenoid supply. I would watch that in the data monitoring section right? Or just on the dash?

It is The on/off type thats programmed in the ecm. He did just put a new fun hub on, but I tried the other settings like ‘variable no speed sensor” & etc just to make sure it wasn’t another type of hub. The other fan program types caused the fan to be on non stop with code 0245 active at low idle.

I tried checking for resistance and grounding at the ecm power cable to help eliminate the starving for power issue. I know once corrosion sets in it can really clog things up.