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I have a 1999 CH with 470 Etec engine. I was on this site a little while ago and had some suggestions to help with my problem but no luck yet.The problem is every time I use the accelorator the fan engauges and when I take my foot off the accelorator most times the fan will disengauge.If I use the cruise control to increase revs the fan stays disengauged .This problem happens weather you are moving or stationary .The dealer has replaced the vechile ECU and all senders that supply ECU. There readouts give no listed faults and the copilot is not showing any faults.Every thing else works perfect. have had auto elecs look and they say every thing tests okay. Some times it will have a good day and the problem is not so bad.This happens weather the engine is hot or cold. thanks for any suggestions....

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I have a 1999 CH with 470 Etec engine. I was on this site a little while ago and had some suggestions to help with my problem but no luck yet.The problem is every time I use the accelorator the fan engauges and when I take my foot off the accelorator most times the fan will disengauge.If I use the cruise control to increase revs the fan stays disengauged .This problem happens weather you are moving or stationary .The dealer has replaced the vechile ECU and all senders that supply ECU. There readouts give no listed faults and the copilot is not showing any faults.Every thing else works perfect. have had auto elecs look and they say every thing tests okay. Some times it will have a good day and the problem is not so bad.This happens weather the engine is hot or cold. thanks for any suggestions....

Mine got to where it would not disengage after it came on (C15 Cat). At first it would stop if you cut the engine off and restart it, then you had to cut it off and let it sit a few minutes, then finally it just ran constantly.

Not only noisy, but i've heard the fan running robs you of 50 horsepower! They replaced the switches but that didn't change anything, had to get a new fan hub-works fine now.

Producer of poorly photo-chopped pictures since 1999.

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I have a 1999 CH with 470 Etec engine. I was on this site a little while ago and had some suggestions to help with my problem but no luck yet.The problem is every time I use the accelorator the fan engauges and when I take my foot off the accelorator most times the fan will disengauge.If I use the cruise control to increase revs the fan stays disengauged .This problem happens weather you are moving or stationary .The dealer has replaced the vechile ECU and all senders that supply ECU. There readouts give no listed faults and the copilot is not showing any faults.Every thing else works perfect. have had auto elecs look and they say every thing tests okay. Some times it will have a good day and the problem is not so bad.This happens weather the engine is hot or cold. thanks for any suggestions....

The way you describe the problem it sounds like it's probably an electrical problem. On the left side of the engine compartment there should be a fuse panel bolted up to the cab bulkhead. This is the EPDM (engine power distribution module). Fuse 41 is located in this box and it supplies power to the fan clutch solenoid. Due to the location of the epdm it had a tendency to get road salt and contamination in it which would cause bad contact across fuses in the box. Take a look at the box and see if the terminals inside look corroded. With the engine running try wiggling the harness coming from the epdm and the harness on the engine as well.

"Mebbe I'm too ugly and stupid to give up!"

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The way you describe the problem it sounds like it's probably an electrical problem. On the left side of the engine compartment there should be a fuse panel bolted up to the cab bulkhead. This is the EPDM (engine power distribution module). Fuse 41 is located in this box and it supplies power to the fan clutch solenoid. Due to the location of the epdm it had a tendency to get road salt and contamination in it which would cause bad contact across fuses in the box. Take a look at the box and see if the terminals inside look corroded. With the engine running try wiggling the harness coming from the epdm and the harness on the engine as well.

Thanks for your help. I have checked the fuses in the EPDM box.I checked fuse 40&41 again they look clean but hard to see the back of terminals inside box.The problem appears to be electrical because the air switch on the side of the radiator is not getting an earth when the fan is engauged &getting an earth when disengauged.If the fan is engauged and you give it a earth it disengauges as long as you hold the earth.This should eliminate a fan hub problem. thanks again....

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Thanks for your help. I have checked the fuses in the EPDM box.I checked fuse 40&41 again they look clean but hard to see the back of terminals inside box.The problem appears to be electrical because the air switch on the side of the radiator is not getting an earth when the fan is engauged &getting an earth when disengauged.If the fan is engauged and you give it a earth it disengauges as long as you hold the earth.This should eliminate a fan hub problem. thanks again....

I take it you're in Australia? The ground for the engine fan is provided by the engine ecu. The ecu controls the ground, and when it sees a request for fan operation it allows the circuit to open or close as needed. It is possible that the ecu is bad, but before proceeding with swapping out the ecu I would check all of the grounds on the engine, starter, alternator, and frame.

"Mebbe I'm too ugly and stupid to give up!"

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Another thing you might do is check and make sure that the fan solenoid is plugged in to the correct connector on the engine harness. I think it is possible to connect it to the ether start connector.

i was just talking to mackpro about my fan, under (hey mackpro) egr. would appreciate your 2 cents

thanks for your time

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had a 1999 Etech in a CX today and the Horton air fan was coming on and off constantly. The water temp was only 180 degrees and the A/C was turned off. Hooked up the laptop and went to "switch status" and could see the A/C pressure coming on then off and the "Fan engage" was doing the same, this will happen even if the A/C is not turned on. Turns out it was a bad A/C high pressure switch. I also looked at the coolant temp and intake manifold temp on the laptop as if these get to high it will also engage the fan. Fuse 41 sends 12 volts to the fan solinoid the it returns back to the Engine ECM where the Engine ECM will ground the return wire. Basicly the Engine ECM makes or breaks the ground to control the fan clutch. It can be a pain to figure out without the laptop and Mack software.

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had a 1999 Etech in a CX today and the Horton air fan was coming on and off constantly. The water temp was only 180 degrees and the A/C was turned off. Hooked up the laptop and went to "switch status" and could see the A/C pressure coming on then off and the "Fan engage" was doing the same, this will happen even if the A/C is not turned on. Turns out it was a bad A/C high pressure switch. I also looked at the coolant temp and intake manifold temp on the laptop as if these get to high it will also engage the fan. Fuse 41 sends 12 volts to the fan solinoid the it returns back to the Engine ECM where the Engine ECM will ground the return wire. Basicly the Engine ECM makes or breaks the ground to control the fan clutch. It can be a pain to figure out without the laptop and Mack software.

coming across wy. sunday nite perty much flat out for 600 miles, grossing 80,000 fan cycled like it was sopose to would lock up around 200 dg and unlock about 175 dg. cycles were about equal on as much as off.

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had a 1999 Etech in a CX today and the Horton air fan was coming on and off constantly. The water temp was only 180 degrees and the A/C was turned off. Hooked up the laptop and went to "switch status" and could see the A/C pressure coming on then off and the "Fan engage" was doing the same, this will happen even if the A/C is not turned on. Turns out it was a bad A/C high pressure switch. I also looked at the coolant temp and intake manifold temp on the laptop as if these get to high it will also engage the fan. Fuse 41 sends 12 volts to the fan solinoid the it returns back to the Engine ECM where the Engine ECM will ground the return wire. Basicly the Engine ECM makes or breaks the ground to control the fan clutch. It can be a pain to figure out without the laptop and Mack software.

Thanks for that Mackpro. I will take it back to the dealer again and mention what you said. Is there any way the A/C high pressure switch can be by passed.The coolant temp makes no difference to the problem. have checked fuse 41 as suggested by rhasler and it has power to the air switch on the radiator but no ground.

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Thanks for that Mackpro. I will take it back to the dealer again and mention what you said. Is there any way the A/C high pressure switch can be by passed.The coolant temp makes no difference to the problem. have checked fuse 41 as suggested by rhasler and it has power to the air switch on the radiator but no ground.

On some trucks (depending on software level in the engine ECM) the dealer can go in to the Engine parameters and uncheck the "air conditioning installed" . This way the Engine ECM ingnores the signal from the A/C high pressure switch and the fan should stay off if the problem lies with the A/C switch. However the 1999 CX I was working didnt have this feature but most newer trucks (2002 I think) do. The dealer should be able to use the laptop to check whats going on unless it is a bad Engine ECM. Does you dash have the fan override switch on it? If your truck has the APADS A/C system this could be the main problem. The APADS is a small square electrical box/ECM that is bolted near the radiator and has flashing lights to tell you the A/C is not working. The wiring on the APADS is so screwey that we always remove them and throw them away.

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On some trucks (depending on software level in the engine ECM) the dealer can go in to the Engine parameters and uncheck the "air conditioning installed" . This way the Engine ECM ingnores the signal from the A/C high pressure switch and the fan should stay off if the problem lies with the A/C switch. However the 1999 CX I was working didnt have this feature but most newer trucks (2002 I think) do. The dealer should be able to use the laptop to check whats going on unless it is a bad Engine ECM. Does you dash have the fan override switch on it? If your truck has the APADS A/C system this could be the main problem. The APADS is a small square electrical box/ECM that is bolted near the radiator and has flashing lights to tell you the A/C is not working. The wiring on the APADS is so screwey that we always remove them and throw them away.

I called into the dealer yesterday there auto elec bypassed the aircon switch which made no difference but it could still be a faulty wire in the loom somewhere. So I have booked it in for the end of next week and hopefully they can solve the problem.It does have a fan override switch on the dash but no APADS. Thanks Again..

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  • 11 years later...
On 8/29/2010 at 8:42 PM, Talca said:

I called into the dealer yesterday there auto elec bypassed the aircon switch which made no difference but it could still be a faulty wire in the loom somewhere. So I have booked it in for the end of next week and hopefully they can solve the problem.It does have a fan override switch on the dash but no APADS. Thanks Again..

I have a 2001 quantum the Horton fan won’t go off but what is confusing the ground wire has power in it. If you push the test light into the earth wire at the selonoid it lights up but gives it a earth and stops the fan. Any ideas?

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57 minutes ago, Brendan leahy said:

I have a 2001 quantum the Horton fan won’t go off but what is confusing the ground wire has power in it. If you push the test light into the earth wire at the selonoid it lights up but gives it a earth and stops the fan. Any ideas?

Sounds like an Earth Issue to me. get a Multimeter & see the earth wire has a Short in It..

Maybe disconnect/remove existing earth wire & run a new one..!

"Be who you are and say what you feel...
Because those that matter...
don't mind...
And those that mind....
don't matter." -

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so youre fan has the little brass control vale on the left side of the radiator, right?  If so,  under normal conditions, when you shut the engine off, (air pressure above 90 psi), the fan blade will spin until the 7 second electrical shut down time is up, then the blade locks.  if so, it locks when power is taken away.  is this happening, the fan locks when power is off to the celenoid...  Bare with me on this,  and yes the A/C is connected to the system. power should be at the pressure switch waiting for the switch to react to pressure, which will turn the fan on to cool the grill condensor..   I hope some of my friends here fill in any blanks I  have, jojo

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Yes that is correct Joey it needs power and earth to open the selonoid / brass valve which let’s air go to the fan hub and pulls it out of gear. But just putting a new earth wire on does disengage the fan but then I don’t think it will come on at all is my worry. I sort of had the idea that the earth must be controlled from something else like your ac pressure and engine temp. 

Edited by Brendan leahy
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Ever try adding additional ground (earth) wires ?  like batteries to frame, cab to frame..... engine to frame. Adding some wires as grounds seems kinda a cheap try as compared to stuff you tried and didn't work. Extra ground wires won't hurt anything even if they don't cure it.

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I have grounded the EECU a few times in the passed to ensure good grounding of the EECU....  anyway, MarkT is right... I have always said,,," you can't have too many ground's"..... jojo

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