My sprinkler system has 7 zones... but for some reason when it hits zone 4, it shuts the entire system off. I feel like it shorts out, but it doesn't throw the breaker in the fuse box. So, I tried just skipping that zone - and that seems to work (otherwise the system shuts off entirely and I have to hit the manual reset). There was some landscaping done in and around zone 4... what do you think is going on?
Do you know where the zone #4 valve is located? If not you may need to call an irrigation company that has a wire tracer to find it.
Once the valve is located, disconnect the common and the zone wire from the solenoid.
Using an ohm meter, read the resistance of the solenoid. If it reads below 20 ohms, replace the solenoid.
If the solenoid reads between 20-60 ohms, then the problem is elsewhere.
It is possible that the #4 zone wire and the common got scraped, and they are touching somewhere. Hopefully not, as that would require digging up the wire and visually inspecting it.
You can go here for more information on sprinkler problems.