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James W
James W, Small Engine Troubleshooting Expert
Category: Small Engine
Satisfied Customers: 3700
Experience:  7 years as Mechanic & Parts Manager for Brother who has Owned Lawn & Garden Repair shop for 35 years
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I have a john deere L120 lawn mower and the pto has gone haywire

Resolved Question:

I have a john deere L120 lawn mower and the pto has gone haywire . Took the clutch off and had it checked , showed that it was working fine . Bought a new pto switch yesterday , installed it , still would'nt work . Was tinkering with it last night and when I pulled the pto switch on and stood up off the seat , it acted like it wanted to engage the blades , but it would also kill the engine . Another thing I have noticed is that after I start the engine , I can leave the seat without the engine dying without engaging the parking brake . I have tried bypassing the seat safety switch . Not having much luck !!! I sure would appreciate some help . Thanks much !!!
Submitted: 3 years ago.
Category: Small Engine
Expert:  James W replied 3 years ago.

James W :

Greetings, My name isXXXXX and I am here to help the best I can. My goal is 100% satisfaction. Let's get started.

James W :

After starting.. Many of these mowers will run if you do not have the parking brake engaged

James W :

as long as the mower deck is not on and the tractor is in neutral

James W :

so this is likely not the problem

James W :

You are going to think I am Nuts here, but

James W :

I think you may just need a new battery

Customer:

One thing for sure , previously it would not run without engaging parking brake if you left the seat

James W :

OK..

James W :

I have heard that

Customer:

are you still there

James W :

But the electromagenet on the PTO clutch

James W :

sorry important phone call from soon to be ex wife..

James W :

back now

Customer:

no prob

James W :

the PTO clutch requires a LOT of power (amperage

James W :

there is another electromagenet under the carburetor that shuts the fuel flow off when the key is turned off

James W :

(or when you get off the seat)

James W :

It uses power, then stops using power when you get up

Customer:

i have never had this prob before when the battery needed to be replaced

James W :

this allows enough power to operate the switch as soon as the power stops flowing to the carb afterflow solenoid

James W :

Does not always act this way... This happens when there is enough power in the battery start the mower, but not enough to power the pto switch and the fuel solenoid

James W :

It could also be that the chargin system is not quite keeping things up to snuff

James W :

This is a common enough problem that I have put to gether a premade answer for PTO's

Customer:

why would it not make a sound until i raised up off of seat ?

James W :

It just does not have enough power to operate the switch..

James W :

Electricity will follow the path of least resistance.

James W :

it will go through the carb solenoid because it is easier than going through the PTO

James W :

Here is my STANDARD PTO answer.. Not all will apply here, but I just wanted you to know it is a very common problem

James W :

First. a battery problem will cause major trouble with the PTO. It takes an enormous amount of battery energy to run an electric clutch. So if your battery is low...or goes down, the pto cannot work. Even if there is enough power to start the engine.


 


If you bought a battery from a discount store. There is a good possibility that either the battery was bad right off the shelf or that it didn't have the required 350 cca that is the minimum for an electric clutch to work correctly for any length of time.


 


If the battery keeps going down, you could also have a problem with the charging system. Just a note about charging systems in a lawn mower. YOU CANNOT EVER JUMP-START A LAWNMOWER WITH AN AUTOMOBILE OR YOU WILL RUIN THE CHARGING SYSTEM OF THE MOWER. tHE SYSTEM OF THE CAR WILL BLOW THE MOWER'S CHARGING SYSTEM.


 


You'd have to have the charging system in the mower checked.


 


The PTO switch could also be bad causing this problem. This happens fairy often.


 


Also check the wires that attach to the pto clutch. If they came loose, it won't work. Also check for any corrosion on any of the wire terminals and also the battery post and terminals. Also check to make sure that there is not corrosion on the ground cables.


 


Last but not least, the PTO itself could be bad.... or at least need adjusted...if it has an adjustment. If you have an adjustable clutch, the setting is .010" between the two halves of the clutch...(in between the slots)


.

Customer:

give me just a min on typing , not to good at it : )

James W :

no problem.. I am actually eating lunch right now, so enjoying the break (so to speak). Crab Cakes and corn on the cob.

Customer:

had the clutch (pto) checked , it showed good , have never jumped it with vehicle

James W :

I expected the Clutch to be good. Other reasons for charging system to go bad other than jumping.. But, I do not think that is the problem either..

Customer:

you dont think it is likely a safety switch , the freaky way it is acting ?

James W :

I am more believeing it is a connection problem, bad ground, bad battery terminal, frayed wire partially grounding out, bad ignition switch (where it has developed a resistance), or the bad batttery.

James W :

You can test the safety switch with a meter..

Customer:

i know for a fact that before it would not run without setting the brake if you raised up off the seat

James W :

But, the confusing part is that it that it does not die when you let go of the parking brake...

James W :

Does it die if you are Drving and get up off the seat?

Customer:

no

James W :

Does you unit have a Module that all the safety features go in to (a small circuit board or replay?

James W :

Might have been a mid year change

James W :

if so, the moduel could also be bad

James W :

There IS a safety switch built INTO the PTO unit..

James W :

It is Possible for the PTO to work, without the Safety switch built in not working.

Customer:

not sure , its a 2002 L120 john deere , that has already cost me a bundle of money , fixing to roll it of a cliff LOL

James W :

Just do not drop it on anyone's Head.. Not worth Jail time.

Customer:

LOL no doubt

James W :

I am going to transfer the question to Q&A MODE..

James W :

I want to bounce this one off my more experienced brother (37 years running one of largest dealers in state). Sales and service..

Customer:

ok thanks

James W :

We will not be able to instant chat anymore, but we will both be notified via email of replies and follow ups

James W :

His shop does not close for another couple hours and I KNOW he is very busy this time of year.

James W :

I was Moving today, not helping..

James W :

but, saw your question, finished moving, thought I would help

James W :

As soon as I get his opinion, one of us will post here again.

James W :

We should be able to get you fixed up

Customer:

only prob is i need it quick , yard looking terrible

James W :

If it is a safety switch, you can try this..

James W :

I expect that you have a problem with the safety switch under the seat


it is there so that if you are Driving and fall off the seat, it stops the mower from driving off or driving over you


also known as a dead man switch


trains have them too for obvious reasons


I would look at the switch and see if it is being engaged all the way when you sit on the seat


sometimes brackets get bent out of shape of the mounting is just off a bit and you can bend it back to make the switch engage


other times, the switch is broken and you have to replace the switch


Still other times, the connectors are loose on the switch (or off) and need to be taken off, then put back on so the wires are actually connected to this Kill switch.,


You should also examine all wires going to the switch from the switch all the way back to the other end


make sure there are no frayed wires


That would be true of the safety switch on the brake / clutch and the mower PTO switch as well as any that would detect if the rider is in gear


But, the seat switch is designed to kill the engine if you let go of the brake or start up the mower blades without being on the seat


Frankly, I would check ALL the switches the same way, but start with the seat switch because I am betting my $8.50 on it


Dang, I forgot to say, sometimes the switch is just bad and will not "SWITCH".


you check that with a meter.


then replace the switch if it will not switch between open and closed


 

James W :

Also, you can jump the battery to a Vehicle that is NOT running at all. POST to POST + to + and neg to neg

James W :

Then start the mower with Both batteries hooked up

James W :

see if the PTO will run then..

James W :

If it does, Get a new battery or check the connections to the mowers battery

Expert:  James W replied 3 years ago.
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Expert:  James W replied 3 years ago.
I have converted the question to Q&A Mode rather than chat. I will be available for additional follow-up questions. If my answers have not been acceptable, please let me know what more I can do. I will be notified via email of your responses even after you Hit ACCEPT.
Expert:  James W replied 3 years ago.

OK, after a conference call with my brother, and his head mechanic in combination with me finding a wiring diagram for your unit, we think we have a 90% answer.

 

MP31/MP31758________UN06JUN03.gif

 

 

Here is a wiring diagram

 

WIRING HARNESS (SN 060001- )TMBR>WIRING HARNESS (SN 060001- ) (CONTINUED)

CartKEYPART NO.PART NAMEQTYSERIAL NO.235235EREMARKS
1........TERMINAL1HEADLIGHT
2R77477TERMINAL1BRAKE
3M76268CLIP1
4T28586TERMINAL1PTO CLUTCH
5R77477TERMINAL1RIO SWITCH
6........TERMINAL1SEAT SWITCH
7AM117324SWITCH1XXHEADLIGHT
AM131760ROCKER SWITCH1XINVERTER RESET
8AM127393SWITCH1PTO
9M79858BOOT1
CartKEYPART NO.PART NAMEQTYSERIAL NO.235235EREMARKS
10AM104884SWITCH1BRAKE
11M63389RIVET2BRAKE SWITCH
M67899RIVET2RIO SWITCH
12M94087STRAP2060001-110000
13AM127226SWITCH1RIO
14M112368SUPPORT3
1537H142SCREW30.164" X 1"
16AM132500MODULE1IGNITION CONTROL, (SUB FOR AM130341)
17M110159NUT1
18AM131841KEY1IGNITION, (SUB FOR AM101600)
CartKEYPART NO.PART NAMEQTYSERIAL NO.235235EREMARKS
1957M7328ELEC. CONNECTOR HOUSING1HOURMETER
20........TERMINAL1IGNITION SWITCH
21........TERMINAL1CONTROL MODULE
22........TERMINAL1GROUND
23........TERMINAL1ALTERNATOR
24........TERMINAL1FUEL SOLENOID
25AM127825POWER CORD1RIO SWITCH
26........TERMINAL1OIL PRESSURE SWITCH
27........TERMINAL1GROUND
28AM124397WIRING HARNESS1X(JUMPER FROM MAIN HARNESS TO ENGINE)
CartKEYPART NO.PART NAMEQTYSERIAL NO.235235EREMARKS
AM132207WIRING HARNESS1X(JUMPER FROM MAIN HARNESS TO ENGINE)
29........TERMINAL1(TO MAIN WIRING HARNESS)
30........TERMINAL1DISCHARGE MODULE
31M71224NUT2
32AAM131703HOUR METER1060001-110000(SUB AM134577)
32BAM134577HOUR METER1110001-
AM133189HOUR METER1110001-REPLACEMENT
33........TERMINAL1PTO SWITCH
34........TERMINAL1HEADLIGHT SWITCH
35AR62407BULB2INSTRUMENT PANEL
CartKEYPART NO.PART NAMEQTYSERIAL NO.235235EREMARKS
36AM108844SOCKET KIT3
37T72143TERMINAL1ENGINE CONNECTOR
38AM131690WIRING HARNESS1060001-110000XMAIN
AM133652WIRING HARNESS1110001-XMAIN
AM131836WIRING HARNESS1XMAIN (W/INVERTER)
39........EYELET1GROUND
40........TERMINAL1BATTERY
41M43835TERMINAL1STARTER
4224M7054WASHER1110001-
..AM107087KIT1FUSIBLE LINK
CartKEYPART NO.PART NAMEQTYSERIAL NO.235235EREMARKS
..........FUSE215 AMP (IGNITION MODULE)

 

 

Expert:  James W replied 3 years ago.

From what we see, there is a module on your unit called an RIO which is a switch that will NOT let the mower engage (or will kill the engine) when you try to mow in reverse.

 

We believe that you may have a multi pronged problem that may be feeding off each other.

 

You may have a bad RIO module (prevents mowing in reverse)

AND / Or your unit may have a bad or mis adjusted safety switch that detects to see if the transmission is in Reverse.

AND / OR you may have a bad seat switch..

AND / Or there may be a problem with the wiring harness.

 

I hope this helps

James W, Small Engine Troubleshooting Expert
Category: Small Engine
Satisfied Customers: 3700
Experience: 7 years as Mechanic & Parts Manager for Brother who has Owned Lawn & Garden Repair shop for 35 years
James W and 8 other Small Engine Specialists are ready to help you

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