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bgsengineclinic, Small Engine Technician
Category: Small Engine
Satisfied Customers: 220
Experience:  Over 20 years of experience in Small engine repair, Kohler Certified Expert Technician, Self-Employed in my own dealership.
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Kohler pro 18 hp cv492s Lawn mower cranks but no start Spark

Customer Question

Kohler pro 18 hp cv492s
Lawn mower cranks but no start
Spark plug has spark only when kill wire off
Not getting power to fuel solonoid
All wiring has been tested for continuity- ok
How do we test for voltage for fuel solonoid?
All switches and relays test ok
Submitted: 4 years ago.
Category: Small Engine
Expert:  bgsengineclinic replied 4 years ago.

bgsengineclinic :

OK to start with, resistance or continuity checks prove very little.. To test for voltage at the solenoid, disconnect it, turn key on, and using test light (12V ) or multi meter (Assuming you have one, since you claim to have checked all switches and solenoids, etc.) set on DC volts , red probe (or test light probe) to the wire that hooked to solenoid (the wire that does not bolt to the engine, if there were 2) and the other end to battery negative (-) post and see if it shows 12V or the test light lights. If it does, then you have 12V to the solenoid, and likely have a bad ground connection. If not, then you may have a blown fuse or simply a bad key switch (which would also explain the no spark without coil wire unhooked)

bgsengineclinic :

As I see youve gone offline, I'll switch this to Q&A and we can work on this as time is found.


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Customer: replied 4 years ago.
Starter solonoid had voltage to it with test light as per your test
Tried new ig switch still no spark unless kill wire off
Have cleaned and checked ground wires ,continuity ok?
We are novices, not sure how to test which wires for voltage
Yes we tested all wires for continuity but not sure about voltage
Customer: replied 4 years ago.
We also did a bypass test from fuel solonoid to direct power at starter solonoid
Fuel solonoid clicked,turned key,engine started( kill wire was still off coil )
Expert:  bgsengineclinic replied 4 years ago.
Oh OK.. no need to be concerned with testing any voltages if the engine will crank over. If the engine produces no spark, it is not voltage related - this engine will have a Magneto ignition. The rest of this post is assuming that your continuity tester is either a Multimeter, or a battery powered continuity light. (only way to really check continuity!)

Here's what to do - use your continuity checker and unhook kill wire from the coil, Turn the key to "on" position , engine not running, set the parking brake, make sure the Power Takeoff (P.T.O.) - AKA the mower deck is OFF , and see if there is continuity from the kill wire end that hooks to coil, and the engine ground. If there is, then turn key off, and at the outside of the engine, find the multi-pin connector that attaches engine into the machine's wiring harness, and disconnect or separate that connector. - Again, check for continuity to the engine block from the coil kill wire. If you still have continuity, then you have a short to ground in the engine wiring harness. If it is open circuit (no continuity) then engine harness is fine, hook kill wire back to coil, and we know we're only having to deal with the machine's wiring harness.

Trace the kill wire from the coil to the connector, and note which pin of the connector is the kill wire. Then find the matching pin in the other half of the connector, and using that for your test point, check for continuity to any good ground (engine block, battery - post, etc) and see if you have continuity to ground with key in "on" position - you likely will if you are at this point. Next, leaving tester hooked up , find and unplug the connector from the switch and see if the continuity to ground goes away. if it does, you have a bad switch, if it does not, then you have a bad PTO switch or a bad Seat switch, or the wiring harness at some point has been pinched or rubbed through and shorted to ground.
Customer: replied 4 years ago.
We don't understand the last test
you say to find and unplug connector from switch to see if continuity to ground goes away??
Which switch?
We have used a new ig switch and have changed the clutch/ brake switch and the blade engagement switch
We tested the seat switch and it works
All wires work
All the wiring has been checked with analog ohm meter and visually and all show continuity and no shorting of ground wire
Expert:  bgsengineclinic replied 4 years ago.
OK. well it is fairly simple - Since it is a magneto ignition that kill wire must be touching ground; if it is preventing spark, it has continuity to ground.

When everything is operating correctly, key on, that wire should be open circuit from any location (if it is not hooked to coil) - I.E. zero continuity or infinity ohms. If that wire has a path to ground, then it is going to kill the ignition , which is why you have spark when you disconnect it from the coil. Therefore, it is finding a path to ground at some point - so if it is not shorted on the engine wiring harness side (that's the test where you disconnect the engine harness from tractor harness) the short to ground must logically be on the tractor's wiring harness - the short may be through a bad (or incorrect) switch, (Key switch, seat switch, pto switch, etc) or by way of a pinched, cut, broken, or frayed wire somewhere in the harness.

Disconnecting the plug from the key switch eliminates a bad switch , (assuming the continuity to ground is still present) - likewise disconnecting the other switches should do the same - if all switches are disconnected, and your ground / kill wire circuit continues to show continuity to ground, even with the tractor harness isolated, then you have a short to ground somewhere in the harness.

Basically it is a step by step process of elimination beginning at the connector where it hooks to the coil, and working backwards, attempting to isolate each portion of the kill wire circuit as simply as possible.. So... we start at the kill wire where it hooks to coil, test for continuity to ground, and assuming that is present, isolate the engine harness, and re-test - if the continuity is present, there's a short circuit in the engine harness shorting the kill wire to ground. If it goes away, then the issue has been isolated to the tractor's harness or switches. The first and *usually* easiest switch to check is the key switch - and if you unplug that and the short to ground goes away, you either have the wrong switch, a bad switch, or something got mis-wired. :) - From that point it is a matter of unplugging the switches that affect the ground circuit , usually seat switch and/or PTO switch or clutch/brake switch. if the continuity to ground is still present with all those switches eliminated, then the short is in the tractor harness at some point. Either way , disconnecting kill wire from coil means the ground circuit in either the engine harness or tractor harness is shorted to ground at some point, which kills the spark.
Customer: replied 4 years ago.
We unhooked the black wire from starter solonoid switch and still with ohm ends attached to the
Ground and the kill wire the continuity remains
Customer: replied 4 years ago.
Thank you for all the info
We will have to look at those things the next day or two and keep in touch
Holly and Peter
Challenged DIY people!!!!
Expert:  bgsengineclinic replied 4 years ago.
OK.. Starter solenoid will not have anything to do with this system - There are multiple black wires in the system - The kill wire to the coil is just one of them - It should go to a white 6 or 8 pin connector with several other wires on the engine . That connector plugs in to the tractor wiring harness.

You have a Canadian built sears tractor so I cannot access any wiring diagram information - I'm covering this from memory - wiring for US built tractors will be the same.

For the moment ignore the starter solenoid, that will not have anything to do with the ignition system.

In the dash panel you will have a key switch , also in dash will be a PTO switch (Presumably, if your machine has electric clutch PTO) , and under seat will be seat switch... ) - we'll worry about those later, too.

The tractor wiring harness connects to the engine by way of a white connector with many wires connected in together.

Separate that connector into the engine harness and the tractor harness. (physically separate the connector) - Then, using your ohm meter, connect the red probe of meter to the coil kill wire (which is unhooked from coil) and connect the other probe to bare metal on the engine block. Do you get a continuity reading? (of any amount other than Infinity - or "0L" ) Lets just do one test at a time :)

If you get any continuity at all, then the ground wire is shorted somewhere at the engine - You'll need to trace the wire from ignition coil back to the connector and inspect for any rubbed through or pinched or cut wire insulation.

Lets get the results of that test first and then we can move on to the next test. :) We have time, so you can just do one step at a time and get back with me, and I'll help you work through it. Perhaps I will be able to dig out a wiring diagram for a similar U.S. Built sears (I believe I have one parked in the "Boneyard" that may just match up - I have to check tomorrow, and if it does, then I can get you the diagram *and* color coding of wires..)
Customer: replied 4 years ago.
Hi again
We did the test with ohm meter and kill wire with ground
We get no continuity
We also have engine harness connector unplugged at same time
We have checked all wiring for fraying or bare wires touching
We see nothing
Expert:  bgsengineclinic replied 4 years ago.
OK.. your engine harness would be fine if it is unplugged at both ends and no continuity to ground, so the issue is with the tractor harness.

Next step is to test the tractor harness ground to see what is killing the engine - trace the kill wire from coil to the harness plug, and unplug the harness , noting which pin is the grounding circuit , from there, use ohm meter on that pin (tractor harness side) , turn key to "on" position and see if there is continuity to ground in that circuit - If there is, leave the test meter hooked up, and then it will be a matter of unplugging connectors from switches one by one I would start with unplugging the easiest to access - likely either the Key switch. if unplugging one results in the continuity to ground going away you have found the problem (note: Have some weight - at least 100 Lbs , or a helper, sitting in the tractor seat) - If unplugging one switch does not make the problem go away, try the next one (probably PTO switch or seat switch) - Note that some Seat switches will automatically ground the circuit causing a shutdown if they are unplugged (if you look closely down in the connector you may notice a spring loaded shorting bar that shorts across the terminals when unplugged) If none of the switches being unplugged results in continuity to ground going away, unplug them all and also the clutch/brake switch , (and make a bypass pin using a piece of milk jug plastic to bypass the seat switch shorting bar if there is one.. or you can clip one wire with wire cutters and re-assemble it with splice connector later) - if the continuity to ground is still there, there *must* be a short circuit in the system somewhere - pinched wire, etc. However if at any of those disconnect points, the continuity to ground goes away, then you have found what is causing the engine to not start.

Also review owner's manual for what must happen to start engine (operator in seat, PTO disengaged, clutch engaged, etc)
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Customer: replied 4 years ago.
Results from 1st test
Show kill wire in harness plug,key on,ohm meter to harness plug and ground show no continuity.
If key turned off shows continuity
It seems to operate as it should.??
Expert:  bgsengineclinic replied 4 years ago.

OK. Now, we will *repeat* this test , however - This time you will turn the key to the "Start" position , and see if you get continuity. (Note: The engine may begin to spin over, so be watchful of being near the spinning flywheel! - Optionally you can disconnect the starter cable from the starter or unplug the solenoid wire from the starter) - If you do, then a starting circuit switch (if not the key switch itself) is causing the problem , But If you still show no continuity while the key is turned to "Start" position, then everything *should* be working as it is supposed to, and I would then say , hook it all back up and see if engine starts.. it should, if it started and ran with the ground wire unhooked from coil. If it does not, then something really is not making sense.. (Or, the connector plug itself that plugs tractor to engine harness may be bad! Try inspecting it and see if there's any melting or discoloration..)

Customer: replied 4 years ago.
We tested again with ohm meter to ground of machine harness and other end to ground
Key in on position reads 2000 ohms and stays there in the start position
Expert:  bgsengineclinic replied 4 years ago.
OK. then there's a short to ground in the system - Either a switch is grounding (Is someone in seat when doing that test? - Try the test with seat switch unplugged, or if it has electric PTO clutch, unplug the connector from that switch under dash) or there's a short in your wiring harness, not necessarily to external surface. I would try it will seat switch unplugged , (and check the connector plug to see if it has the shorting bar I mentioned before)
Customer: replied 4 years ago.
We isolated each switch to test separately
PTO switch gives reading when it is plugged in and ohm tested(we unplugged seat switch)
When we plugged in seat switch and unplugged the PTO
We get a reading with ohm test to kill wire at machine harness and ground??same test for each switch separately
Expert:  bgsengineclinic replied 4 years ago.

OK.. Lets look at how the ground circuit operates (in most cases, cant tell for sure without a wiring diagram for your machine) - When operator is in seat, opening the seat switch, PTO disengaged, clutch pedal depressed, and key to run position, all circuits to ground for the grounding circuit are open. If operator leaves seat with the PTO on, or with the parking brake NOT set (which typically holds the brake pedal down) the ground circuit will complete through either or both switches when the seat switch closes .

So.. Basically you need to first test making sure operator is in seat, brake depressed (for starting) and PTO switch off. If there is continuity to ground, one of those switches is not working properly. If you sit in the seat and let off brake pedal, there should be NO continuity to ground (likewise with PTO switch on) because the seat switch interrupts the ground circuit. If that is not the case, seat switch is bad.

If continuity to ground is gone with operator in seat, then everything *should* be working normally. - if not, then seat switch is still completing a circuit somewhere, or it is shorted, or one of the wires is shorted.

Its difficult to be accurate without any wiring diagram information, though.. if it comes down to it, I can opt out and maybe a Canadian expert can take it over, if they have access to wiring diagrams for that model.

Customer: replied 4 years ago.
As per the tests the ohm meter reads 2000 ohms
It doesn't go to zero
We can email you the wiring diagram??
Expert:  bgsengineclinic replied 4 years ago.

I believe you can upload it to JustAnswer and link to it here, or alternatively you can upload it to a file sharing service I believe - we're not permitted to provide email address or contact information here. it should be a paperclip icon just above the response reply box where you type replies (I think)

That would be helpful for sure - 2000 ohms means you have continuity in the circuit, although there is a resistance, you won't want 0 ohms either (indicating continuity) , but instead want the display to be "0L" or similar. (same reading you get with the probes not touching anything) . Also keep in mind that holding the probes bare ends in your hands can also result in a false reading, so don't touch the metal probes when holding them to the circuits.. (I can hold bare probes in my fingers of each hand and get a reading of .589 MegOhms resistance just from the conductivity of the human body)

and finally, make sure and "zero" your meter by touching the test probes together and reading the ohms resistance reading, which you subtract from any readings you do get from circuit testing.

But if you can get a diagram uploaded somehow, it would be extremely helpful.

Customer: replied 4 years ago.
wiring schematicgraphic
Expert:  bgsengineclinic replied 4 years ago.
Looks like another attempt in order - didn't appear to "stick" or upload completely.. worst case, you can do a bing search on my username or business name or upload to photobucket and link to that..
Customer: replied 4 years ago.
Customer: replied 4 years ago.
Customer: replied 4 years ago.
I have tried a scan--wont accept a PDF file.
I then took a photo with my I phone--downloaded it and tried to sent it--I presume a jpeg file??
There has got to be a simple way of sending a wiring diagram????
Expert:  bgsengineclinic replied 4 years ago.

Best bet would be take photos and upload the photos to (its free) and then you should be able to link to them in here. Alternative is a file sharing site such as It would be simpler if I could just write out my email address, but it'd be a violation of the website rules.. Or you could run a bing search on my username, find my website and contact form and go from there as well.

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Customer: replied 4 years ago.
Hi there Brian

I did email your website in an effort to be able to send you the wiring diagram
While I was doing that ,my husband miraculously found the problem,
It seems the switches he got from Sears(correct part number) did not bench test the same as the old ones--he thought his old ones were bad--so replaced them
He decided to check them again today and put the old ones back in the machine and voila!! the lawnmower had spark and started.
There were also some dusty areas on a couple of contacts that he cleaned yesterday and also helped the relays to click again.
so--thanks for your good technical assistance.