Index: src/vehicle_func.h
===================================================================
--- src/vehicle_func.h	(revision 12166)
+++ src/vehicle_func.h	(working copy)
@@ -19,7 +19,7 @@
 
 typedef void *VehicleFromPosProc(Vehicle *v, void *data);
 
-void VehicleServiceInDepot(Vehicle *v);
+void VehicleMaintenanceInDepot(Vehicle *v);
 void VehiclePositionChanged(Vehicle *v);
 Vehicle *GetLastVehicleInChain(Vehicle *v);
 uint CountVehiclesInChain(const Vehicle *v);
@@ -68,7 +68,9 @@
 Money GetTrainRunningCost(const Vehicle *v);
 
 bool VehicleNeedsService(const Vehicle *v);
+bool VehicleNeedsUpdate(const Vehicle *v);
 
+
 uint GenerateVehicleSortList(const Vehicle*** sort_list, uint16 *length_of_array, VehicleType type, PlayerID owner, uint32 index, uint16 window_type);
 void BuildDepotVehicleList(VehicleType type, TileIndex tile, Vehicle ***engine_list, uint16 *engine_list_length, uint16 *engine_count, Vehicle ***wagon_list, uint16 *wagon_list_length, uint16 *wagon_count);
 CommandCost SendAllVehiclesToDepot(VehicleType type, uint32 flags, bool service, PlayerID owner, uint16 vlw_flag, uint32 id);
Index: src/train.h
===================================================================
--- src/train.h	(revision 12166)
+++ src/train.h	(working copy)
@@ -307,4 +307,6 @@
 	void OnNewDay();
 };
 
+Money EstimateTrainCost(EngineID engine);
+
 #endif /* TRAIN_H */
Index: src/ship_cmd.cpp
===================================================================
--- src/ship_cmd.cpp	(revision 12166)
+++ src/ship_cmd.cpp	(working copy)
@@ -144,9 +144,9 @@
 
 static void CheckIfShipNeedsService(Vehicle *v)
 {
-	if (_patches.servint_ships == 0 || !VehicleNeedsService(v)) return;
+	if (!VehicleNeedsService(v)) return;
 	if (v->IsInDepot()) {
-		VehicleServiceInDepot(v);
+		VehicleMaintenanceInDepot(v);
 		return;
 	}
 
@@ -368,7 +368,7 @@
 	RecalcShipStuff(v);
 
 	PlayShipSound(v);
-	VehicleServiceInDepot(v);
+	VehicleMaintenanceInDepot(v);
 	InvalidateWindowData(WC_VEHICLE_DEPOT, v->tile);
 	InvalidateWindowClasses(WC_SHIPS_LIST);
 }
@@ -398,9 +398,13 @@
 	return (t < v->progress);
 }
 
-static CommandCost EstimateShipCost(EngineID engine_type)
+/**
+ * Return cost of building a new ship
+ * @param engine_type Type of ship to build
+ */
+Money EstimateShipCost(EngineID engine_type)
 {
-	return CommandCost(EXPENSES_NEW_VEHICLES, GetEngineProperty(engine_type, 0x0A, ShipVehInfo(engine_type)->base_cost) * (_price.ship_base >> 3) >> 5);
+	return GetEngineProperty(engine_type, 0x0A, ShipVehInfo(engine_type)->base_cost) * (_price.ship_base >> 3) >> 5;
 }
 
 static void ShipArrivesAt(const Vehicle* v, Station* st)
@@ -815,7 +819,7 @@
 
 	if (!IsEngineBuildable(p1, VEH_SHIP, _current_player)) return_cmd_error(STR_SHIP_NOT_AVAILABLE);
 
-	value = EstimateShipCost(p1);
+	value = CommandCost(EXPENSES_NEW_VEHICLES, EstimateShipCost(p1));
 	if (flags & DC_QUERY_COST) return value;
 
 	/* The ai_new queries the vehicle cost before building the route,
Index: src/roadveh.h
===================================================================
--- src/roadveh.h	(revision 12166)
+++ src/roadveh.h	(working copy)
@@ -82,4 +82,6 @@
 
 void RoadVehUpdateCache(Vehicle *v);
 
+Money EstimateRoadVehCost(EngineID engine_type);
+
 #endif /* ROADVEH_H */
Index: src/aircraft.h
===================================================================
--- src/aircraft.h	(revision 12166)
+++ src/aircraft.h	(working copy)
@@ -127,4 +127,6 @@
 	void OnNewDay();
 };
 
+Money EstimateAircraftCost(EngineID engine);
+
 #endif /* AIRCRAFT_H */
Index: src/train_cmd.cpp
===================================================================
--- src/train_cmd.cpp	(revision 12166)
+++ src/train_cmd.cpp	(working copy)
@@ -642,9 +642,14 @@
 	}
 }
 
-static CommandCost EstimateTrainCost(EngineID engine, const RailVehicleInfo* rvi)
+/**
+ * Compute cost to construct a new train
+ * @param engine: Train to build
+ */
+Money EstimateTrainCost(EngineID engine)
 {
-	return CommandCost(EXPENSES_NEW_VEHICLES, GetEngineProperty(engine, 0x17, rvi->base_cost) * (_price.build_railvehicle >> 3) >> 5);
+	const RailVehicleInfo *rvi = RailVehInfo(engine);
+	return GetEngineProperty(engine, 0x17, rvi->base_cost) * (_price.build_railvehicle >> 3) >> 5;
 }
 
 static void AddRearEngineToMultiheadedTrain(Vehicle* v, Vehicle* u, bool building)
@@ -702,7 +707,7 @@
 
 	if (rvi->railveh_type == RAILVEH_WAGON) return CmdBuildRailWagon(p1, tile, flags);
 
-	CommandCost value = EstimateTrainCost(p1, rvi);
+	CommandCost value = CommandCost(EXPENSES_NEW_VEHICLES, EstimateTrainCost(p1));
 
 	uint num_vehicles =
 		(rvi->railveh_type == RAILVEH_MULTIHEAD ? 2 : 1) +
@@ -2254,7 +2259,7 @@
 		}
 	}
 
-	VehicleServiceInDepot(v);
+	VehicleMaintenanceInDepot(v);
 	InvalidateWindowClasses(WC_TRAINS_LIST);
 	v->PlayLeaveStationSound();
 
@@ -3614,9 +3619,9 @@
 
 static void CheckIfTrainNeedsService(Vehicle *v)
 {
-	if (_patches.servint_trains == 0 || !VehicleNeedsService(v)) return;
+	if (!VehicleNeedsService(v)) return;
 	if (v->IsInDepot()) {
-		VehicleServiceInDepot(v);
+		VehicleMaintenanceInDepot(v);
 		return;
 	}
 
Index: src/ship.h
===================================================================
--- src/ship.h	(revision 12166)
+++ src/ship.h	(working copy)
@@ -16,7 +16,7 @@
 /**
  * This class 'wraps' Vehicle; you do not actually instantiate this class.
  * You create a Vehicle using AllocateVehicle, so it is added to the pool
- * and you reinitialize that to a Train using:
+ * and you reinitialize that to a Ship using:
  *   v = new (v) Ship();
  *
  * As side-effect the vehicle type is set correctly.
@@ -44,4 +44,6 @@
 	void OnNewDay();
 };
 
+Money EstimateShipCost(EngineID engine_type);
+
 #endif /* SHIP_H */
Index: src/roadveh_cmd.cpp
===================================================================
--- src/roadveh_cmd.cpp	(revision 12166)
+++ src/roadveh_cmd.cpp	(working copy)
@@ -125,9 +125,13 @@
 	DrawSprite(6 + _roadveh_images[spritenum], pal, x, y);
 }
 
-static CommandCost EstimateRoadVehCost(EngineID engine_type)
+/**
+ * Compute cost for constructing a new road vehicle
+ * @param engine_type Road vehicle to build
+ */
+Money EstimateRoadVehCost(EngineID engine_type)
 {
-	return CommandCost(EXPENSES_NEW_VEHICLES, ((_price.roadveh_base >> 3) * GetEngineProperty(engine_type, 0x11, RoadVehInfo(engine_type)->base_cost)) >> 5);
+	return ((_price.roadveh_base >> 3) * GetEngineProperty(engine_type, 0x11, RoadVehInfo(engine_type)->base_cost)) >> 5;
 }
 
 byte GetRoadVehLength(const Vehicle *v)
@@ -174,7 +178,7 @@
 
 	if (!IsEngineBuildable(p1, VEH_ROAD, _current_player)) return_cmd_error(STR_ROAD_VEHICLE_NOT_AVAILABLE);
 
-	cost = EstimateRoadVehCost(p1);
+	cost = CommandCost(EXPENSES_NEW_VEHICLES, EstimateRoadVehCost(p1));
 	if (flags & DC_QUERY_COST) return cost;
 
 	/* The ai_new queries the vehicle cost before building the route,
@@ -1373,7 +1377,7 @@
 	if (first) {
 		if (RoadVehFindCloseTo(v, x, y, v->direction) != NULL) return true;
 
-		VehicleServiceInDepot(v);
+		VehicleMaintenanceInDepot(v);
 
 		StartRoadVehSound(v);
 
@@ -1973,9 +1977,9 @@
 static void CheckIfRoadVehNeedsService(Vehicle *v)
 {
 	/* If we already got a slot at a stop, use that FIRST, and go to a depot later */
-	if (v->u.road.slot != NULL || _patches.servint_roadveh == 0 || !VehicleNeedsService(v)) return;
+	if (v->u.road.slot != NULL || !VehicleNeedsService(v)) return;
 	if (v->IsInDepot()) {
-		VehicleServiceInDepot(v);
+		VehicleMaintenanceInDepot(v);
 		return;
 	}
 
Index: src/vehicle.cpp
===================================================================
--- src/vehicle.cpp	(revision 12166)
+++ src/vehicle.cpp	(working copy)
@@ -93,7 +93,11 @@
 /* Initialize the vehicle-pool */
 DEFINE_OLD_POOL_GENERIC(Vehicle, Vehicle)
 
-void VehicleServiceInDepot(Vehicle *v)
+/**
+ * Perform maintenance in a depot
+ * @param v Vehicle to perform maintenance on
+ */
+void VehicleMaintenanceInDepot(Vehicle *v)
 {
 	v->date_of_last_service = _date;
 	v->breakdowns_since_last_service = 0;
@@ -101,7 +105,12 @@
 	InvalidateWindow(WC_VEHICLE_DETAILS, v->index); // ensure that last service date and reliability are updated
 }
 
-bool VehicleNeedsService(const Vehicle *v)
+/**
+ * Does vehicle needs (periodic) maintenance?
+ * @param v Vehicle to check
+ * @return \c true if vehicle should go to the depot for maintenance
+ */
+static bool VehicleNeedsMaintenance(const Vehicle *v)
 {
 	if (v->vehstatus & (VS_STOPPED | VS_CRASHED))       return false;
 	if (v->current_order.type != OT_GOTO_DEPOT || !(v->current_order.flags & OFB_PART_OF_ORDERS)) { // Don't interfere with a depot visit by the order list
@@ -110,15 +119,107 @@
 		if (v->current_order.type == OT_GOTO_DEPOT && v->current_order.flags & OFB_HALT_IN_DEPOT) return false;
 	}
 
+	/* vehicles without break-down, and 'no servicing if not break-down' are never maintained */
 	if (_patches.no_servicing_if_no_breakdowns && _opt.diff.vehicle_breakdowns == 0) {
-		return EngineHasReplacementForPlayer(GetPlayer(v->owner), v->engine_type, v->group_id);  /* Vehicles set for autoreplacing needs to go to a depot even if breakdowns are turned off */
+		return false;
 	}
 
-	return _patches.servint_ispercent ?
-		(v->reliability < GetEngine(v->engine_type)->reliability * (100 - v->service_interval) / 100) :
-		(v->date_of_last_service + v->service_interval < _date);
+	/* Is the game global setting 'maintenance disabled'? */
+	switch (v->type) {
+		case VEH_TRAIN:    if (_patches.servint_trains == 0) return false;
+		case VEH_ROAD:     if (_patches.servint_roadveh == 0) return false;
+		case VEH_SHIP:     if (_patches.servint_ships == 0) return false;
+		case VEH_AIRCRAFT: if (_patches.servint_aircraft == 0) return false;
+		default: break; // Weird vehicle type, don't bother
+	}
+
+	if (v->service_interval == 0) // Vehicle needs no maintenance
+		return false;
+
+	/* Maintenance interval has passed */
+	if (_patches.servint_ispercent) {
+		return (v->reliability < GetEngine(v->engine_type)->reliability * (100 - v->service_interval) / 100);
+	} else {
+		return (v->date_of_last_service + v->service_interval < _date);
+	}
 }
 
+/**
+ * Does vehicle needs an update (renewal or replacement)?
+ *
+ * @param v Vehicle to check
+ * @return \c true if the vehicle should be renewed or (auto)replaced
+ */
+bool VehicleNeedsUpdate(const Vehicle *v)
+{
+	EngineID replace_engine;
+	Player *p = GetPlayer(v->owner);
+
+	if (VehicleHasDepotOrders(v)) return false; // The vehicle will end up in the hangar eventually on it's own
+
+	/* Does an engine replacement exist for this vehicle? */
+	replace_engine = EngineReplacementForPlayer(p, v->engine_type, v->group_id);
+	if (replace_engine == INVALID_ENGINE) {
+		if (!p->engine_renew) return false; // autorenewal switched off
+		if ((v->age - v->max_age) < p->engine_renew_months * 30) {
+			/* Player has autorenewal switched off, or the vehicle is not old enough => No need to replace it */
+			return false;
+		}
+		/* autorenew means replacing the engine with one of the same type */
+		replace_engine = v->engine_type;
+	}
+
+	/* Either the engine should be replaced, or renewed.
+	 * Next question, is it useful to do now?
+	 */
+	if (!IsEngineBuildable(replace_engine, v->type, v->owner)) {
+		/* Engine is not buildable anymore */
+		return false;
+	}
+
+	/* Since p may be different from _current_player, the DoCommand and the
+	 * CmdBuild*vehicle*() functions cannot be used here
+	 */
+	Money money_needed;
+	switch (v->type) {
+		case VEH_TRAIN:    money_needed = EstimateTrainCost(replace_engine); break;
+		case VEH_ROAD:     money_needed = EstimateRoadVehCost(replace_engine); break;
+		case VEH_SHIP:     money_needed = EstimateShipCost(replace_engine); break;
+		case VEH_AIRCRAFT: money_needed = EstimateAircraftCost(replace_engine); break;
+		default: return false; // Weird vehicle type, don't bother replacing/renewing it
+	}
+
+	if (p->player_money < (p->engine_renew_money + (2 * money_needed))) {
+		/* We lack enough money to request the replacement right away.
+		 * We want 2*(the price of the new vehicle) and not looking at
+		 * the value of the vehicle we are going to sell.
+		 * The reason is that we don't want to send a whole lot of
+		 * vehicles to depots when we only have enough money to replace
+		 * a few.
+		 * Remember this happens in the background so the user can't stop this.
+		 */
+		return false;
+	}
+
+	/* We found no reason NOT to replace/renew the vehicle so we will send it there at once */
+	return true;
+}
+
+/**
+ * Decide whether vehicle needs service (needs to go to a depot).
+ * A vehicle may need service either for maintenance or for an update (a renewal or replacement).
+ * @param v Vehicle to check.
+ * @return \c true if service is needed, \c false otherwise.
+ */
+bool VehicleNeedsService(const Vehicle *v)
+{
+	return VehicleNeedsMaintenance(v) || VehicleNeedsUpdate(v);
+}
+
+
+
+
+
 StringID VehicleInTheWayErrMsg(const Vehicle* v)
 {
 	switch (v->type) {
@@ -2211,7 +2312,7 @@
 	v->vehstatus |= VS_HIDDEN;
 	v->cur_speed = 0;
 
-	VehicleServiceInDepot(v);
+	VehicleMaintenanceInDepot(v);
 
 	TriggerVehicle(v, VEHICLE_TRIGGER_DEPOT);
 
Index: src/aircraft_cmd.cpp
===================================================================
--- src/aircraft_cmd.cpp	(revision 12166)
+++ src/aircraft_cmd.cpp	(working copy)
@@ -234,9 +234,14 @@
 	height = spr->height;
 }
 
-static CommandCost EstimateAircraftCost(EngineID engine, const AircraftVehicleInfo *avi)
+/**
+ * Compute cost of constructing a new aircraft
+ * @param engine Aircraft to build
+ */
+Money EstimateAircraftCost(EngineID engine)
 {
-	return CommandCost(EXPENSES_NEW_VEHICLES, GetEngineProperty(engine, 0x0B, avi->base_cost) * (_price.aircraft_base >> 3) >> 5);
+	const AircraftVehicleInfo *avi = AircraftVehInfo(engine);
+	return GetEngineProperty(engine, 0x0B, avi->base_cost) * (_price.aircraft_base >> 3) >> 5;
 }
 
 
@@ -276,8 +281,7 @@
 {
 	if (!IsEngineBuildable(p1, VEH_AIRCRAFT, _current_player)) return_cmd_error(STR_AIRCRAFT_NOT_AVAILABLE);
 
-	const AircraftVehicleInfo *avi = AircraftVehInfo(p1);
-	CommandCost value = EstimateAircraftCost(p1, avi);
+	CommandCost value = CommandCost(EXPENSES_NEW_VEHICLES, EstimateAircraftCost(p1));
 
 	/* to just query the cost, it is not neccessary to have a valid tile (automation/AI) */
 	if (flags & DC_QUERY_COST) return value;
@@ -287,6 +291,8 @@
 	/* Prevent building aircraft types at places which can't handle them */
 	if (!CanAircraftUseStation(p1, tile)) return CMD_ERROR;
 
+	const AircraftVehicleInfo *avi = AircraftVehInfo(p1);
+
 	/* Allocate 2 or 3 vehicle structs, depending on type
 	 * vl[0] = aircraft, vl[1] = shadow, [vl[2] = rotor] */
 	Vehicle *vl[3];
@@ -704,9 +710,9 @@
 
 static void CheckIfAircraftNeedsService(Vehicle *v)
 {
-	if (_patches.servint_aircraft == 0 || !VehicleNeedsService(v)) return;
+	if (!VehicleNeedsService(v)) return;
 	if (v->IsInDepot()) {
-		VehicleServiceInDepot(v);
+		VehicleMaintenanceInDepot(v);
 		return;
 	}
 
@@ -1551,52 +1557,13 @@
 		}
 	}
 
-	VehicleServiceInDepot(v);
+	VehicleMaintenanceInDepot(v);
 	SetAircraftPosition(v, v->x_pos, v->y_pos, v->z_pos);
 	InvalidateWindowData(WC_VEHICLE_DEPOT, v->tile);
 	InvalidateWindowClasses(WC_AIRCRAFT_LIST);
 }
 
-/** Checks if an aircraft should head towards a hangar because it needs replacement
- * @param *v the vehicle to test
- * @return true if the aircraft should head towards a hangar
- */
-static inline bool CheckSendAircraftToHangarForReplacement(const Vehicle *v)
-{
-	EngineID new_engine;
-	Player *p = GetPlayer(v->owner);
 
-	if (VehicleHasDepotOrders(v)) return false; // The aircraft will end up in the hangar eventually on it's own
-
-	new_engine = EngineReplacementForPlayer(p, v->engine_type, v->group_id);
-
-	if (new_engine == INVALID_ENGINE) {
-		/* There is no autoreplace assigned to this EngineID so we will set it to renew to the same type if needed */
-		new_engine = v->engine_type;
-
-		if(!p->engine_renew || (v->age - v->max_age) < p->engine_renew_months * 30) {
-			/* No need to replace the aircraft */
-			return false;
-		}
-	}
-
-	if (!HasBit(GetEngine(new_engine)->player_avail, v->owner)) {
-		/* Engine is not buildable anymore */
-		return false;
-	}
-
-	if (p->player_money < (p->engine_renew_money + (2 * DoCommand(0, new_engine, 0, DC_QUERY_COST, CMD_BUILD_AIRCRAFT).GetCost()))) {
-		/* We lack enough money to request the replacement right away.
-		 * We want 2*(the price of the new vehicle) and not looking at the value of the vehicle we are going to sell.
-		 * The reason is that we don't want to send a whole lot of vehicles to the hangars when we only have enough money to replace a single one.
-		 * Remember this happens in the background so the user can't stop this. */
-		return false;
-	}
-
-	/* We found no reason NOT to send the aircraft to a hangar so we will send it there at once */
-	return true;
-}
-
 ////////////////////////////////////////////////////////////////////////////////
 ///////////////////   AIRCRAFT MOVEMENT SCHEME  ////////////////////////////////
 ////////////////////////////////////////////////////////////////////////////////
@@ -1731,7 +1698,7 @@
 	AircraftNextAirportPos_and_Order(v);
 
 	/* Send the helicopter to a hangar if needed for replacement */
-	if (CheckSendAircraftToHangarForReplacement(v)) {
+	if (VehicleNeedsUpdate(v)) {
 		_current_player = v->owner;
 		DoCommand(v->tile, v->index, DEPOT_SERVICE | DEPOT_LOCATE_HANGAR, DC_EXEC, CMD_SEND_AIRCRAFT_TO_HANGAR);
 		_current_player = OWNER_NONE;
@@ -1783,7 +1750,7 @@
 	AircraftLandAirplane(v);  // maybe crash airplane
 
 	/* check if the aircraft needs to be replaced or renewed and send it to a hangar if needed */
-	if (CheckSendAircraftToHangarForReplacement(v)) {
+	if (VehicleNeedsUpdate(v)) {
 		_current_player = v->owner;
 		DoCommand(v->tile, v->index, DEPOT_SERVICE, DC_EXEC, CMD_SEND_AIRCRAFT_TO_HANGAR);
 		_current_player = OWNER_NONE;