if(!IsPlayerInAnyVehicle(playerid))
{
  SendClientMessage(playerid, 0xFFFFFFAA, "SERVER: You must be in the vehicle.");
  return 1;
}
else
{
  new Float:health, vehicleid;
  vehicleid = GetPlayerVehicleID(playerid);
  GetVehicleHealth(vehicleid, health);
  if(health < 900)
  {
    RepairVehicle(vehicleid);
    SendClientMessage(playerid, 0xFFFFFFAA, "SERVER: Your vehicle is repaired.");
  }
  else
  {
    SendClientMessage(playerid, 0xFFFFFFAA, "SERVER: Your vehicle's health is not below 900, so you can't repair it.");
  }
}

forward repaircar()

public OnGameModeInit()
{
SetTimer("repaircar",3000,1);
}

public repaircar()
{
     for(new i=0; i < MAX_PLAYERS; i++)
	{
       new Float:hp[MAX_PLAYERS];
       GetVehicleHealth(GetPlayerVehicleID(i),hp[i]);
       if (hp[i] < 900)
      {
         SetVehicleHealth(GetPlayerVehicleID(i),1000);
         GameTextForPlayer(i,"~w~Vehicle~g~ Repaired",3000,3);
      } 
    }
}