Command Pro CH740 only runs if you hold the key in START position

glwilliams58

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  • / Command Pro CH740 only runs if you hold the key in START position
While mowing yesterday, my CH740 27hp shut off.

From that point on it would start each time I turned the key, then shut off.
I checked the oil level thinking it may be a safety sensor for low oil. Level was fine.
I check the fuel filter, thinking it may be running out of gas. Filter and fuel flow was fine.

It will start every time you turn the key to START, but as soon as you let go of the key and it goes back to the ON position, it shuts off.

I found that if you hold the key in the start position, it will continue to run as long as you hold the key in the start position.

What do you think is causing this problem?

Thanks,

GW
Sarasota Florida
Scag Turf Tiger STT52V 27CH
2006 Command Pro 27
Model# CH740
Approx 720hrs
 

Fish

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  • / Command Pro CH740 only runs if you hold the key in START position
Probably the keyswitch is coming apart internally. I would unplug it immediately and test it, as it could damage your ignition coils,
and they are expensive.
 

glwilliams58

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  • / Command Pro CH740 only runs if you hold the key in START position
Thanks Fish.

I am replacing the ignition key switch. It seems to make sense that this could be the issue. I don't really have a way of testing the old one and a new one is only $14 including shipping.

Is there anything else that you think could be causing it to shut off after it is running? It starts fine every time, but immediately shuts off when you let go of the key and it returns to the ON position.

Are there any sensors that detect unsafe oil or hydraulic pressure that will force the shut down of the motor as soon as it starts?

I have reviewed all of the other safety switches (seat, brake, left and right steering levers, blades) and all appear to be fine. They all stop the mower from starting if they are in an unsafe position. I am not aware of any other safety switches.

Is it possible to temporarily bypass this ignition key without damaging the electrical system or the engine?

Thanks,

GW
 

ILENGINE

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  • / Command Pro CH740 only runs if you hold the key in START position
Possibly a low oil pressure shutdown switch. On the CH series it is normally located in the valley between the cylinders, kinda under the carb. May try unplugging it and see what happens.
 

Fish

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  • / Command Pro CH740 only runs if you hold the key in START position
Find and post the Kohler's "spec" numbers. Scag used a lot of Kohler's with a feature called "SmartSpark" and they were nothing but trouble! So hold off from ordering new parts just yet, as the fix may take some work....I prefer testing and making sure before buying expensive parts.
 

glwilliams58

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  • / Command Pro CH740 only runs if you hold the key in START position
Spec number: CH740-0041
Serial Number: 3622114311

Thanks

G
 

glwilliams58

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  • / Command Pro CH740 only runs if you hold the key in START position
Here is some more info if it helps.

Family: 6KHKS.725 2GC

Looking up the CH 740-0041 this is a 25HP 725cc engine.

GW
 

gfp55

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  • / Command Pro CH740 only runs if you hold the key in START position
Find and post the Kohler's "spec" numbers. Scag used a lot of Kohler's with a feature called "SmartSpark" and they were nothing but trouble! So hold off from ordering new parts just yet, as the fix may take some work....I prefer testing and making sure before buying expensive parts.

Here is some more info if it helps.

Family: 6KHKS.725 2GC

Looking up the CH 740-0041 this is a 25HP 725cc engine.

GW
Give fish some time, he should be able to get you run down on some tests before you start buying anything, Be patient.
 

Fish

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  • / Command Pro CH740 only runs if you hold the key in START position
Give fish some time, he should be able to get you run down on some tests before you start buying anything, Be patient.

No, yesterday, I slipped into a beer-coma early after eating some great chili, so my stepping out was unavoidable and certainly
excusable........

Unfortunately, your engine does have SmartSpark, so that may complicate things a bit...

Ignition
 

Fish

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  • / Command Pro CH740 only runs if you hold the key in START position
On a normal mower's wiring, when you turned the key to the "off" position, or got off the seat while the deck was running, or a few other scenarios, that would send to your coils a connection to "ground" through the switches, which would shut the engine off.

Same as a pushmower, but only the switch is hooked up to the lever, when you let it go, it "grounds" out the coil and shuts the engine down, been that way for a loooonnnggg time......

And that is the beauty of these engines, whenever the flywheel rotates through the coil field, it produces a spark, if the system is working correctly, the only way to stop that is to ground out the coil...

On the circuitry of a keyswitch, it sends voltage to the starter to "crank" when the key is turned to the crank position. It also
does not let the ignition to ground at this position, it also lets voltage go to the fuel solenoid at this position, so the engine
will start and all....

And when the key snaps back to the "run" position, it still does not allow the system to "ground"/shut off... But still allows power to the fuel solenoid, and the rest of the tractor....

And when the key is turned off, the ignition coil is grounded, and the engine shuts down.....

But Kohler, in their great wisdom came up with "SmartSpark", which requires voltage to the SAM unit to run as well, and confuses us poor rednecks all to pieces.......

So I hate to tell you that you might want to be patient with us here, as we are old disgruntled pharts, that don't get paid a dime,
and truth be told, didn't get paid enough before, when we worked on this crud for a living......

So, be patient, one of us here might slip a pearl in this smelly oyster bed..... But if you want to get serious about it, go buy a decent multi-meter, so we can test the keyswitch.
 
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