[sleepysnowflake]

pawn Код:

forward Repair(playerid);
public Repair(playerid)
{
    if (IsPlayerInAnyVehicle(playerid))
    {
        new Float:health;
        new vehicleid = GetPlayerVehicleID(playerid);
        GetVehicleHealth(vehicleid, health);
        if (health <= 999)
        {
            RepairVehicle(vehicleid);
        }
    }
}

Far more simple ?
NOTE: this will not be enabled or disabled by a command. It will fix all the time.