Question about John Deere L100 Series

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Engine stops running when I engage the blades

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  • Kprime
    Kprime Apr 18, 2015

    Hi Fred Peltier, I want to help you with your question, but I need more information from you. Can you please add details in the comment box? Hi Fred. I am working on an answer for you. Should post tomorrow.



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"The engine stops running when I engage the blades". I am going to assume that you do not have a frozen bearing, or two, and the cutting deck is in fine operating condition. I am also going to assume your engine is in good working order and is not simply dying under the load. That only leaves an electrical problem/solution.

Regardless of what mower you own this happens when a path is completed from the kill terminal of the coil back to ground. So diagnosing the problem amounts to tracing the ground wire and the switches it passes through. This is a somewhat complex, multi-path problem. Whenever possible, I will simplify the answer.

The ground circuit, or engine kill system, on all JD 100 series and many other mowers, is conceptually the same. This holds true whether you have an electric clutch or engage the blades manually by moving the blade lever. However there is a minor difference between the automatic transmission (Hydro tranny) and the manual transmission which we will discuss at the end. In either case, there are two possible scenarios. Your problem will be from a faulty seat switch and maybe the wiring related to that switch. OR, your problem will be the RIO Switch (part of the reverse safety system, the one on the transmission) and maybe the related wiring

Shortcut: If you want to skip all the reading and go straight to the answer, just replace your Seat Switch and your RIO Switch (the one on the tranny, not the button you push). If the wiring is good, and it usually is, your problem will be gone.

Senario #1
A white wire runs from a terminal on the coil. This is the engine kill wire. When it is grounded by any means, the coil can no longer produce spark. If your engine starts and runs this wire is fine. If your engine dies when you engage the blades, the problem is not with this wire.

The white wire goes to the Key Switch and provides a path to kill the engine when you turn the key off. Your problem is not here either (Not the Key Switch or white wire). We know this because the engine starts and runs. If this part of the system was bad the engine would not run.

This white wire branches off via another piece of white wire and runs to one terminal on the PTO switch. As long as the blade lever is down, or the PTO switch is down (electric clutch) there is no ground connection inside the PTO switch and the engine remains running. Again, there is no short in the white wire and the PTO switch is good. (Good meaning the PTO is not creating a shorted ground scenario).

When you engage the PTO, either way, an internal connection is made with a second terminal on the PTO switch. This terminal has a white wire with a black stripe (Wht/Blk). The Wht/Blk wire runs to a terminal on the RIO Latch Relay (it's a little black box with no buttons up under the dash/hood). In scenario #1, your problem has nothing to do with the Reverse Operation switches. The ground path we are currently tracing does not go through the RIO Latch, it merely passes by a terminal on that latch. How? The Wht/Blk wire is joined at the RIO latch terminal with another wire. This second wire is a black wire with a white stripe (Blk/Wht). At this point this RIO terminal is just a convenient place to tie the two wires together. Sooo, Wht/Blk turns into Blk/Wht. Don't try tracing these wires with a beer in your hand.***At this point the engine is still running and there are no "bad wires or switches". (We will come back to this terminal point later in the discussion to discuss the alternative pathway, scenario #2)

The Blk/Wht wire leaves the RIO latch terminal and goes to the Seat Switch. If the operator is on the seat and the switch is good, inside the Seat Switch there is no connecting path. However, if the operator stands up, or the switch is bad, a connection is made, internally, to the exit terminal on the seat switch, which has a solid black (blk) wire.

The blk wire runs to a terminal on the transmission RIO Switch; otherwise known as the "kill the mower if you try to mow going backwards switch". This switch is typically located on the transmission (or the gear linkage on a manual tranny). The purpose of the switch is to monitor the transmission linkage for reverse activity. At this terminal there is a second black wire. That black wire goes directly to ground. So your problem once again has nothing to do with the Reverse Operation System; it is simply a convenient place to combine the two wires. In other words, once the pathway makes it through the Seat Switch, it has a direct path to ground and your engine dies.

To sum scenario #1 all up:

  1. White wire from coil to PTO switch.
  2. Activate the PTO and Wht/Blk connects at RIO to Blk/Wht.
  3. Blk/Wht bypasses RIO Latch and goes straight to Seat switch.
  4. Seat switch bad or seat unoccupied, connection made to Blk wire.
  5. Black wire goes straight to ground.
  6. Engine dies
If your engine is running and you activate the PTO a connection for the ground path is supposed to be made. However, that connection should be interrupted while you are in the seat. BUT, if the Seat Switch fails to interrupt the pathway, BOOM, engine dies.

Senario #2
RIO = Reverse Implement Option. Fancy name for "mow while you are backing up". There are 3 elements to the reverse safety system.
  1. RIS button, the button you push to allow you to mow in reverse.
  2. RIO Latch, a black box with an electromagnetic switch that changes the ground path when you press the RIS button.
  3. RIO Switch, a switch which reacts to your reverse linkage and creates the final step in the path to ground.
Now, the other much less likely but still possible pathway, involves a problem with the RIO Switch (#3); the one on the transmission. All of scenario #1 holds true until you get to the branching wire at the RIO Latch Relay (#2). The branch line through the seat switch may be just fine, BUT there is a normally closed pathway through this RIO Latch.

As in the discussion of the original pathway, the ground path arrives at the RIO Latch via the Wht/Blk wire. In the 1st scenario it branches off via the Blk/Wht wire and heads off to the seat. In this 2nd scenario the pathway goes straight through the RIO Latch (a normally closed path) and exits a terminal, on the RIO Latch with a solid white wire. Yep, another white wire.

This white wire goes to the RIO Switch; yes the one on the transmission, where it has its very own terminal and does not have to share.

The purpose of the RIO Switch is to monitor the transmission linkage for reverse activity. Internally, the switch is normally open. This means there is normally NO path to ground; unless you attempt to go backwards. When you attempt to reverse a connection is made inside this switch. It connects the white wire with the black wire (the same black wire that comes from the seat switch) and boom, you're dead.

Should this RIO switch fail, it could be stuck in the closed position. This will not stop your engine from starting and running normally. However, it will kill the engine anytime you activate the PTO. Fortunately, there is a real simple way to test this switch. There is a slight difference in the procedure between the manual tranny and the hydro tranny.

  1. Sit in the seat.
  2. Start your engine.
  3. If manual transmission, push in and hold the brake/clutch DOWN, and shift into any forward gear. If you have a Hydro tranny leave the break/clutch UP.
  4. NOTE: if you activate the PTO at this point, an engine with your problem will die.
  5. HOLD in the backup button (RIS, reverse implement switch)
  6. WARNING: Be prepared for the blades to start.
  7. While holding down the RIS button, ACTIVATE the PTO.
  • If the blades start and the engine keeps running, the problem is your RIO Switch, yes the one on the transmission.
  • If the blades start and the engine dies, the problem is your Seat Switch.
  • NOTE: once you do this, the RIO Latch remains active and the engine will not die; even if you turn the blades on and off repeatedly. The Blades Will BE Active at all times (with the PTO on). The Rio Latch will not reset until you turn the engine off with the key. So once you have tried this test you have to turn the key off in order for your original symptoms to reappear. That's another verification that your problem is this switch.

For the Curious, why does this test work? Because the ground path through the backup safety system can be broken by holding down the RIS button which causes a ground path break inside the RIO Latch Relay. The RIS and the RIO Latch Relay work anytime you hold down the button.

The RIS switch needs a path to ground in order to work. On a manual tranny it gets this path when the clutch is fully depressed. On a hydro tranny it gets this path when the brake/clutch is fully released. Once the RIS button activates the RIO Latch, through a ground provided by the PTO, it remains active via the bypass ground at the RIO Latch terminal with the Blk/Wht wire.

The RIS and RIO Latch don't know, or care, if you are in reverse they just work when told to; and when they are activated the ground path through the reverse system is interrupted. Because the path is broken in the RIO Latch Relay, this test assumes the RIO Latch Relay, the Reverse button (RIS), and the associated wiring are in working condition.

WHEWWWW, done and done.

Posted on Apr 18, 2015

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Make should your blades turn easy

Posted on Apr 18, 2015


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