Of the hondas ive seen, they all have the diode in the fuse box. Ive looked at the skematic, and its in the starter relay circuit.
What purpose does it serve? Is it to keep the starter from spinning when the motor is running, and the starter button is depressed? If its bad (open in both directions) what would be the symptoms? If it were shorted in both directions(i dont think it can be ) what would be the symptoms?
I know a diode works like a one way valve..it only allows current to flow thru it in one direction...and i know how to inspect it, im just curious as to why its in the circuit. Ive tried looking at the service manuals and tech books...but its something that i havent seen discussed.
Anyone know?

 

The diode on a 400ex prevent the neutral light from coming on when the clutch is pulled. It prevents the flow of electricity from the bulb to ground through the clutch switch. Anytime the start button is pushed, the starter relay will engage if either the neutral switch, or the clutch switch is made. With the diode the only time the neutral light is on, is when the neurtal switch is made. Without the diode, pulling the clutch would also turn on the neutral light. I fthe diode were open, the relay would engage with the clutch switch made, but not with the neutral switch made, although the neutral light would still work.

You almost have to be looking at the wiring diagram to follow the path.

Think of the diode as a check valve. Current will only flow in one dirrection. The diode's purpose is to prevent current flow in the opposite direction to ground, but allow two paths to ground in the other direction.

If you are having trouble understanding this, I can scan a diagram and label it for you that might make it easier to understand.

Kirk

 

Interesting, thanks.

 

Hey, that would be great, ill pm my email address.

 

i think another reason they do that is so if you have an accidental short to ground before the diode, it wont make the ICM go into fits about thinking the trans is in neutral, because i think it changes your spark advance and stuff when you are in neutral vs. in gear. that and i think the rev-limiter might be lower in neutral to keep people from blowing up their engines by revving them too much with no load. if that diode wasnt there and you had a short somewhere it would think it's in neutral all the time and maybe cause some problems.

 

I'm not sure which wiring diagram you are referring to, but on a 400 ex the icm has no clue as to what gear the transmission is in. The neutral safety switch is only in the start circuit. It acts only to keep the neutral light turned off when the clutch is pulled.

K

 

The original post mentions Honda's in general, I was not reffering to just the 400 ex. I'm sure you're right about that model since it has the manual clutch system. I was referring to most of the utility quads, like my 04 rancher.

 

Heres an update.
I found an article in the july 05 issue of nuts and volts, an elctronics magazine, which explained the use and purpose of the diode.
Its to keep the flyback voltage from spiking the ecu. Once i looked closer at the print, I saw the diode is in parallel with the starter solinoid.
When you let off the starter button,the field in the solinoid, collaspes, and induces a voltage spike, of opposite polarity, back into the circuitry. The speed of the collaspe determines the voltage peak. It can be way more than 12 volts, and its the opposite polarity, so the diode is there to block the backward flowing volage to the circuitry of the ecu.