bad ground to fan selenoid switch

one advice... if a2 out is faulty do not fix ore change ECM, rerprogram to any unused out and repin connector

 

The inputs that control the fan on a DDECIII/IV are;
Coolant Temperature Sensor,
Oil Temperature Sensor,
Air Inlet Temperature,
Aux Fan Control(normally closed aircond high pressure switch),
Fan Override Switch(optional normally open dash switch).

You need to put a laptop or reader on it to check the inputs, and fan output.

Is your fan solenoid wired to the usual A2 terminal of the 30-pin ECM vehicle connector?

Does the fan unlock if you ground this wire at the connector?

If it does, there are two reasons for the fan staying locked;
1/ the ECM is receiving an input that requires the fan to be locked,
2/ the ECM has a faulty output.

What is the resistance of the fan solenoid?

The fan wire can be shifted to a spare output, if available, and the ECM can be reprogrammed to suit, but this doesn't always work. I assume this is because something in the ECM's brain regarding the fan operation has been corrupted. Some ECM's that have had the fan output shifted develop other problems at a later date, and end up having to be replaced.

 

I do check auxially fan input with DDRS to be sure

 

i know this is old but if it helps others. Freightliners with series 60 use 2 dirent fan hubs one is an open and one a closed. if some replaces with wrong hub or replace fan switch the system will not work right. These systems use 3 varibles. 1 fan hub 2 fan switch 3 ecm program. all 3 need to be matched. if one is worng the fan will stay on or stay off. the ecm controls the ground feed to the swtich. they use a always open or a always closed switch matched to the fan hub. if your hub and switch match than you need to reprogram the ecm to them or change the hub and switch to match the ecm. we spent 3 days working on one just to call freightliner and find out the ecm we put on was programed backwards and was cutting the ground and keeping the fan on.

 

Much needed help. Thanks for posting!

 

I just changed ecm, Freightliner 1995 12.7 Detroit with ddec3 and I put ddec4 that they reprogramed in order to work. And fan is always on. Is it possible that they programmed it not correctly?