Cooling fan won't shut off except in 4x4

[TacMac2012]

I have a 1078 that the engine fan won't shut off. Not even when flipping the fan switch. My buddy has driven the truck more than I have, he said the fan shuts off if the truck is put in 4x4, this is what has me stumped. Everything appears to be hooked up.

 

[redman333]

I have a 1078 that the engine fan won't shut off. Not even when flipping the fan switch. My buddy has driven the truck more than I have, he said the fan shuts off if the truck is put in 4x4, this is what has me stumped. Everything appears to be hooked up.

Do these have a fan solenoid. If so unplug it and see if the fan shuts off.


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[Suprman]

The fan solenoid is normally closed which keeps the fan on. Unplugging it should keep the fan on. Sounds like an electrical issue. Maybe a ground somewhere.

 

[redman333]

The fan solenoid is normally closed which keeps the fan on. Unplugging it should keep the fan on. Sounds like an electrical issue. Maybe a ground somewhere.

So they do have them. I ask because you can get different solenoids that are normally open or closed so if he unplugs it and the fan stops someone may have replaced it with the wrong one. Also can check for power at the solenoid to see if it has power or not.


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[319cssb]

So does that mean the Cooling fan is off all the time? Because FMTV have permanent 4x4 wheel drive. Last time I checked on mine anyway.
-Check if the circuit breaker is tripped CB22 if not then
-find the cooling fan solenoid behind the passenger kick panel.
take off the connector and check for continuity . then check fo voltage on the plug. supply voltage from a source and see if the solenoid engages. if it works then
-deplete air from tanks and remove air line from cooling fan solenoid. if air pressure builds , shut off the truck.
-Remove Solenoid and replace.

 

[redman333]

View attachment 753812
So does that mean the Cooling fan is off all the time? Because FMTV have permanent 4x4 wheel drive. Last time I checked on mine anyway.
-Check if the circuit breaker is tripped CB22 if not then
-find the cooling fan solenoid behind the passenger kick panel.
take off the connector and check for continuity . then check fo voltage on the plug. supply voltage from a source and see if the solenoid engages. if it works then
-deplete air from tanks and remove air line from cooling fan solenoid. if air pressure builds , shut off the truck.
-Remove Solenoid and replace.

I’m guessing he means when you press mode on the keypad to lock it in 50/50 mode.


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[319cssb]

Are you the OP? How come you always inject your opinion in other people's posts? They can answer for themselves, you know.

 

[redman333]

Are you the OP? How come you always inject your opinion in other people's posts? They can answer for themselves, you know.

Always, I haven’t been on here in almost a year. Plus you can use your brain also instead of being condescending to the op since we all know the vehicle has all time 4x4.


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[319cssb]

Always, I haven’t been on here in almost a year. Plus you can use your brain also instead of being condescending to the op since we all know the vehicle has all time 4x4.


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So why did you have to make your educational comment, if we all know that.
Good bye and good luck. #ignorelist

 

[redman333]

Wow sorry to the op for that little temper tantrum. Don’t ignore him he does have some good points. One thing to add to his in case it’s not obvious. He mentions checking continuity, I’m assuming he means checking continuity on the solenoid itself not the harness. Since I guess he’s ignoring me now he may not specify that.


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[TacMac2012]

I plan to work on diagnosing on this tomorrow or sometime next week.

The fan stays locked on in normal operation, it only unlocks when it is in 'mode'. If anyone has ever driven one of these trucks off road you know that unless you press the 'mode' button you sure don't have front wheels pulling much if at all...

 

[319cssb]

I plan to work on diagnosing on this tomorrow or sometime next week.

The fan stays locked on in normal operation, it only unlocks when it is in 'mode'. If anyone has ever driven one of these trucks off road you know that unless you press the 'mode' button you sure don't have front wheels pulling much if at all...

Yes, it is a 30/70 distribution, pressing the mode means it goes onto 50/50. The troubleshooting for the cooling fan is in the -30 TM's troubleshooting section. Sometimes it's quicker to get some info beforehand. A hitting the ground running sorta thing.

 

[redman333]

I plan to work on diagnosing on this tomorrow or sometime next week.

The fan stays locked on in normal operation, it only unlocks when it is in 'mode'. If anyone has ever driven one of these trucks off road you know that unless you press the 'mode' button you sure don't have front wheels pulling much if at all...

Yeah the normal operation is supposed to be 30% power to the front wheels and 70 to the rear in normal mode. Then of course in mode it’s 50/50.

The fans not too hard to diag so I’m sure it won’t be too hard.


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[TacMac2012]

just doesn't make sense why it cuts off in 4x4, and stays locked on all the time when in 30/70 (since apparently I have to specify the difference in 4x4 and not 4x4, as if '4x4' is even that, it is still technically only 2x4 as the two tires with least traction are the ones that will spin.

 

[redman333]

just doesn't make sense why it cuts off in 4x4, and stays locked on all the time when in 30/70 (since apparently I have to specify the difference in 4x4 and not 4x4, as if '4x4' is even that, it is still technically only 2x4 as the two tires with least traction are the ones that will spin.

That’s why I was wondering if the wrong solenoid was in there. It may be set so that when In “mode” the fan is set to lock on since you may be driving through rough terrain causing the engine to work harder. So if the solenoid was backwards then it’s operating as it should but opposite of what you need. So you’d just have to swap the solenoid.


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[TacMac2012]

Ahh. Good point. That said, I haven't noticed other trucks keeping the fan 'on' when in 'mode'. But I haven't used 'mode' going very fast that I remember. I will check that though you might be on to something. Could be a couple hoses swapped.

 

[redman333]

Ahh. Good point. That said, I haven't noticed other trucks keeping the fan 'on' when in 'mode'. But I haven't used 'mode' going very fast that I remember. I will check that though you might be on to something. Could be a couple hoses swapped.

Don’t think it’d be a hose swapped. Since the ones I’ve worked on have all been supply in and one hose out. So it’s just an on/off sort of thing. I haven’t worked on the LMTV/FITB though so I can’t say for sure how that works.


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[319cssb]

NewEra, What year is your M1078?
As Suprman already said the fan switch is normally closed, which keeps the fan on. When the solenoid opens the fan stoops spinning. There is no override for off roading other than the Fan switch, which is made to keep the fan from shredding to pieces when it hits water.
Go the logical route check the circuit breaker. Check the current at the plug with the master turned on. Check the ohm reading of the Solenoid,
Then put voltage to the solenoid and see if it engages.
Most of the times it is clogged from dirt. So then you can take it apart and clean it. Other times the plunger will be stuck, then it's time for a new solenoid. There is no way of hooking a solenoid up backwards as the plug only goes in one way.
Hope this helps and with that , I'm out.

 

[redman333]

NewEra, What year is your M1078?
As Suprman already said the fan switch is normally closed, which keeps the fan on. When the solenoid opens the fan stoops spinning. There is no override for off roading other than the Fan switch, which is made to keep the fan from shredding to pieces when it hits water.
Go the logical route check the circuit breaker. Check the current at the plug with the master turned on. Check the ohm reading of the Solenoid,
Then put voltage to the solenoid and see if it engages.
Most of the times it is clogged from dirt. So then you can take it apart and clean it. Other times the plunger will be stuck, then it's time for a new solenoid. There is no way of hooking a solenoid up backwards as the plug only goes in one way.
Hope this helps and with that , I'm out.

This guy is something else. Very arrogant. Not saying he’s wrong just his attitude towards everything.


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[coachgeo]

This guy is something else. Very arrogant. Not saying he’s wrong just his attitude towards everything. ...

not usually...... we all have those days .