🩹 UM2 extruder cooling fan on PJ6 (#23194)

Marlin/src/module/temperature.cpp

     };
 
     uint8_t fanState = 0;
-    HOTEND_LOOP()
-      if (temp_hotend[e].celsius >= EXTRUDER_AUTO_FAN_TEMPERATURE)
+    HOTEND_LOOP() {
+      if (temp_hotend[e].celsius >= EXTRUDER_AUTO_FAN_TEMPERATURE) {
         SBI(fanState, pgm_read_byte(&fanBit[e]));
+        #if MOTHERBOARD == BOARD_ULTIMAIN_2
+          // For the UM2 the head fan is connected to PJ6, which does not have an Arduino PIN definition. So use direct register access.
+          // https://github.com/Ultimaker/Ultimaker2Marlin/blob/master/Marlin/temperature.cpp#L553
+          SBI(DDRJ, 6); SBI(PORTJ, 6);
+        #endif
+      }
+      else {
+        #if MOTHERBOARD == BOARD_ULTIMAIN_2
+          SBI(DDRJ, 6); CBI(PORTJ, 6);
+        #endif
+      }
+    }
 
     #if HAS_AUTO_CHAMBER_FAN
       if (temp_chamber.celsius >= CHAMBER_AUTO_FAN_TEMPERATURE)

Marlin/src/pins/ramps/pins_ULTIMAIN_2.h

 #endif
 
 #ifndef E0_AUTO_FAN_PIN
-  #define E0_AUTO_FAN_PIN                     77
+  #define E0_AUTO_FAN_PIN                     69
 #endif
 
 //