Fan stays on when I floor it.

[blutow]

As I understand it, I should be able to temporariliy disengage the cooling fan for ~15 seconds by flooring the accelerator pedal.

I think my cooling system is working properly otherwise, with the fan kicking on periodically and then disengaging after running for a minute or so.

My assumption is that I have a problem with the time delay module or maybe the throttle position isn't being sensed properly. There is a switch assembly near the back of the motor that I assume is the throttle position sensor. My transmission is kicking down properly (I'm thinking they may share the same throttle switch/sensor, but not sure).

Any tips on troubleshooting? I am still struggling to navigate the TM's, so any help on where to look (or how to search better) is also appreciated.

 

[Action]

I always thought we were supposed to hit pedal to floor and release, not floor and hold it.
The idea is to shut fan off before fording. You wouldnt have the pedal on the floor while entering water.

 

[blutow]

I always thought we were supposed to hit pedal to floor and release, not floor and hold it.
The idea is to shut fan off before fording. You wouldnt have the pedal on the floor while entering water.

I've tried the "mash and release" and also holding it down for ~5 seconds. Neither is releasing the fan. As I understand it, the feature is for 2 things - disengage the fan for fording and also to provide a short boost of extra power when needed. It's not a high priority problem for me, but it bugs me when something isn't working properly.

 

[Glider]

Does your vehicle downshift when you put to floor. If not there is a switch on the throttle linkage under hood to check. I think it also tells the fan to shutoff temporarily.

 

[blutow]

Does your vehicle downshift when you put to floor. If not there is a switch on the throttle linkage under hood to check. I think it also tells the fan to shutoff temporarily.

Yes, transmission is downshifting fine. I wasn’t sure if they share a switch/sensor. I don’t have to floor it to get a downshift, so was thinking there is more going on there with transmission control module. I’ve got a 4 speed if that matters.

 

[Glider]

I'm only familiar with 3 speed.

 

[Mogman]

IIRC the 4 speed does not have a "kickdown switch" because it already knows the throttle position with the TPS, so that switch on the drivers side is the fan switch, you do not want to disable the fan under full throttle especially if it is already calling for fan, there are enough heat issues with those Detroits no need to aggravate the problem.

 

[Action]

I think this is the turbo fan cutoff switch. The Switch is activated when the arm on side of IP hits it.
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[blutow]

IIRC the 4 speed does not have a "kickdown switch" because it already knows the throttle position with the TPS, so that switch on the drivers side is the fan switch, you do not want to disable the fan under full throttle especially if it is already calling for fan, there are enough heat issues with those Detroits no need to aggravate the problem.

Thanks, that makes sense. I'll check the adjustment, I'm guessing it's just not hitting the limit switch. With basically zero miles on my truck since 09 rebuild, I've found quite a few "shake-out" issues like you might expect. Besides some loose bolts and wires and a poorly aligned hood, the brake light switch was so far out of adjustment that it wouldn't operate unless you put all your weight into the pedal.

I hear what you are saying on the heat issues, but I think it's a reasonable feature to have. If the fan is on and you really want the extra HP for a moment (like when trying to merge), ~15 seconds without the fan running isn't going to make or break any heating problems. I think I read that the fan pulls over 20 HP and I can really feel the power drop when it kicks on. On my truck, I find that the fan kicks on even when driving at decent speeds, so it's not like a typical car with "natural" air flow through the radiator. Once the fan kicks on, it's doing it's job well and typically cuts off really quick unless climbing a hill.

Also, it's good to have it for fording capability, even thought I don't plan to use that much. I guess with fording, the assumption is that once you hit the water, your radiator temp drops fast enough that the fan won't kick back on under water after the time delay ends. I could see that being a potential issue if you were running really hot and the water wasn't deep enough to cool the radiator quickly, but deep enough to get the fan blades. I'm guessing most of the soldiers driving these things probably didn't even know about the time delay fan cutoff feature and likely destroyed a few fans.

 

[blutow]

I think this is the turbo fan cutoff switch. The Switch is activated when the arm on side of IP hits it.
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Thanks. I haven't had my doghouse off recently, but I think that is the same or similar to what I have. Looks easy enough to test, I'm guessing it's just out of adjustment.

 

[papakb]

It would have helped if you'd stated which variant and engine your working with. A 998 with a 6.2 and a 3 speed are different in this regard from an 1123 with a 4L80.

 

[diesel_dave]

Thanks, that makes sense. I'll check the adjustment, I'm guessing it's just not hitting the limit switch. With basically zero miles on my truck since 09 rebuild, I've found quite a few "shake-out" issues like you might expect. Besides some loose bolts and wires and a poorly aligned hood, the brake light switch was so far out of adjustment that it wouldn't operate unless you put all your weight into the pedal.

I hear what you are saying on the heat issues, but I think it's a reasonable feature to have. If the fan is on and you really want the extra HP for a moment (like when trying to merge), ~15 seconds without the fan running isn't going to make or break any heating problems. I think I read that the fan pulls over 20 HP and I can really feel the power drop when it kicks on. On my truck, I find that the fan kicks on even when driving at decent speeds, so it's not like a typical car with "natural" air flow through the radiator. Once the fan kicks on, it's doing it's job well and typically cuts off really quick unless climbing a hill.

Also, it's good to have it for fording capability, even thought I don't plan to use that much. I guess with fording, the assumption is that once you hit the water, your radiator temp drops fast enough that the fan won't kick back on under water after the time delay ends. I could see that being a potential issue if you were running really hot and the water wasn't deep enough to cool the radiator quickly, but deep enough to get the fan blades. I'm guessing most of the soldiers driving these things probably didn't even know about the time delay fan cutoff feature and likely destroyed a few fans.

My truck is the same. Most stuff works overall but a few things held together with gum wrappers and toothpicks. I also found the other day that the brake lights don't come on unless you really mash the brakes. I figured oh I'll just adjust the switch. Problem is, with it set so the brakes work properly, the dang transmission torque converter switch is also triggered when not pressing the brake pedal so it looks like I'll need a new switch assembly. Did you make sure both of your switches are okay or just the brake one?

I haven't tried the full throttle fan timeout yet. It pains me to floor the poor old girl. Haha.

One thing I did notice though is the position of the rubber seal flaps under the hood makes a big difference in how often my fan runs. With the flaps folded towards the radiator like it came, the fan ran every few minutes while driving. With the flaps positioned so they actually stand up and seal against the hood, my fan hardly runs. I guess it was both blocking the radiator and also probably sucking in hot engine bay air. So maybe something to check too.

 

[blutow]

Problem is, with it set so the brakes work properly, the dang transmission torque converter switch is also triggered when not pressing the brake pedal so it looks like I'll need a new switch assembly. Did you make sure both of your switches are okay or just the brake one?

I didn't even realize there were 2 switches, I guess I have another thing to check. I guess the torque convertor switch controls the lockout? I'm not sure mine is locking out, I don't feel it doing anything after it gets into 4th.

One thing I did notice though is the position of the rubber seal flaps under the hood makes a big difference in how often my fan runs. With the flaps folded towards the radiator like it came, the fan ran every few minutes while driving. With the flaps positioned so they actually stand up and seal against the hood, my fan hardly runs. I guess it was both blocking the radiator and also probably sucking in hot engine bay air. So maybe something to check too.

Yep, I'll that to my list.

I was able to adjust the switch tonight and it seems to be working now when I mash the pedal (tough testing since it cooled off today). I had to adjust it all the way back and bend the bracket a little to get the switch to engage. I also wasn't getting full throttle to the IP, which was part of the issue. I adjusted the throttle cable to get more travel. While I was messing with it, I was able to massage the throttle return spring solve an idling issue. It was previously idling a little high and the spring had zero tension and wasn't allowing the IP to go all the way to idle. Easy fix on all of it. Not exactly precision engineering on these parts, things had to be bent to make them work.