When I turn the key nothing happens.
There are several elements that go into cranking (turning over) the engine.
- Key Switch (and wiring)
- Starter Solenoid and wires
- Starter motor
Let's start with the battery. The quickest way to make your initial check of the entire starting system and particularly the battery is to get a jump. Yep, get some jumper cables and jump the mower off your car. Turn the key and try to start it in the normal fashion. If it starts cool! It is likely a bad battery.
- Charge the battery for a few hours, on a charger.
- Then perform a voltage measurement of the battery.
- Switch a volt meter to DC Volts and clip it to the battery. It should read between 12-13 volts. If not the battery is suspect.
Now let's check the starting system while bypassing all the safety switches and wiring. How? You can perform this test simply by jumping the starter solenoid. Hold a wrench or fat screwdriver across the two large posts of the starter solenoid. This bypasses the key switch and all safety devices and directly drives the starter. Your starter will crank if the battery and starter are good, the wires and connections are good, and the engine is not locked up. Don't crank it for more that a couple seconds. You just want to verify the battery and the starter are both in good shape. (The engine will crank but not start during this test if the key is off, or if the safety switches or wiring are damaged, or if the safety switches are in the no start/run positions.)
If the starter cranks try one more test. Run a small jumper wire from the positive post of the battery to the little terminal on the solenoid. You may have to take the small wire off the terminal, on the starter solenoid, in order to do this. When you apply this current from the battery to the terminal it should make the solenoid activate and the starter crank. This test bypasses the key switch and shows you the starter system is working. You could do this test first; if it works you do not need to do the basic jump test.
If these tests cause the engine to crank, but it will not crank with the key, then you know you have a problem somewhere in your starter wiring, safety switch system, fuse, or in your Key Switch. Of course you did check the battery terminals for good connection, right?
Most modern riding mowers have the following safety switches:
- Seat switch
- PTO switch
- Reverse switch (RIS) and Reverse Relay (RIO)
- Brake/Clutch switch
If you need detailed instruction for testing your wiring and safety system, I will need your complete machine info.
- Engine Model
- Transmission Model
- Deck Size.
On a John Deere (100 series) the starting current flows through the following items in this order:
- Battery to Fuse then to the Key Switch.
- With key switch in the start position, the current flows from the Key Switch to PTO.
- With PTO off, current flows from the PTO to Brake/Clutch
- With Brake/Clutch Pedal all the way down, the current flows to the starter solenoid.
- If the Starter Solenoid is in good shape, the solenoid connects the battery to the Starter and the engine cranks. Cranking does not mean running; it just means the engine turns over. Running is dependent on many other systems.
Those components are all part of the cranking/starting system. They can prevent the Starter Motor from cranking when you turn the Key Switch. You can trace the voltage with a multi-meter. Connect the black lead to ground and look for 12 volts on each successive step. If the voltage disappears at one particular step, there is your suspect.
Electrical elements that are NOT part of the starting system:
The RIO is the Reverse Implement Option. It is a switch that latches and stays latched under certain conditions. It is activated by the RIS. The RIS is the Reverse Implement Switch. It activates the RIO. These two separate components work to allow the blades to cut while you are backing up (without killing the engine). They have nothing to do with the starting system.
The Seat and the RIO (the reverse latch not the button) switches are tied into the engine kill system.They provide a ground path for grounding the Coil. This same system controls the fuel shut off valve beneath the carburetor. The Seat and RIO can keep the engine from running but they will not prevent the Starter Motor from cranking. Therefore, if you turn the key and nothing happens, the problem has nothing to do with the Seat and Reverse switches.
Note: With the Key in the RUN position, power flows from the Key Switch to the Hour Meter, then to the RIO latch relay (not the RIS button), then to the fuel shut off solenoid. If you do not hear the Fuel Shut off Solenoid clicking on and off when you turn the Key Switch from off to run, there may be a problem in this circuit; including a possible problem in the Hour Meter. Of course none of this affects the cranking circuit. Your engine will still crank, it just won't run.