diff --git a/Marlin/src/HAL/HAL_LPC1768/HAL.cpp b/Marlin/src/HAL/HAL_LPC1768/HAL.cpp
index fedca7a1ff..ac242ca4ab 100644
--- a/Marlin/src/HAL/HAL_LPC1768/HAL.cpp
+++ b/Marlin/src/HAL/HAL_LPC1768/HAL.cpp
@@ -52,11 +52,13 @@ int freeMemory() {
   return result;
 }
 
+// scan command line for code
+//   return index into pin map array if found and the pin is valid.
+//   return dval if not found or not a valid pin.
 int16_t PARSED_PIN_INDEX(const char code, const int16_t dval) {
-  const uint16_t val = (uint16_t)parser.intval(code), port = val / 100, pin = val % 100;
-  const  int16_t ind = (port < (NUM_DIGITAL_PINS >> 5) && (pin < 32))
-                      ? GET_PIN_MAP_INDEX(port << 5 | pin) : -2;
-  return ind > -2 ? ind : dval;
+  const uint16_t val = (uint16_t)parser.intval(code, -1), port = val / 100, pin = val % 100;
+  const  int16_t ind = (port < ((NUM_DIGITAL_PINS) >> 5) && pin < 32) ? GET_PIN_MAP_INDEX((port << 5) | pin) : -2;
+  return ind > -1 ? ind : dval;
 }
 
 void flashFirmware(int16_t value) {
diff --git a/Marlin/src/HAL/HAL_LPC1768/pinsDebug.h b/Marlin/src/HAL/HAL_LPC1768/pinsDebug.h
index 83d8c27fda..af3d7c92e7 100644
--- a/Marlin/src/HAL/HAL_LPC1768/pinsDebug.h
+++ b/Marlin/src/HAL/HAL_LPC1768/pinsDebug.h
@@ -40,6 +40,12 @@
 #define PRINT_PIN(p) do {sprintf_P(buffer, PSTR("%d.%02d"), LPC1768_PIN_PORT(p), LPC1768_PIN_PIN(p)); SERIAL_ECHO(buffer);} while (0)
 #define MULTI_NAME_PAD 16 // space needed to be pretty if not first name assigned to a pin
 
+// pins that will cause hang/reset/disconnect in M43 Toggle and Watch utilities
+//  uses pin index
+#ifndef M43_NEVER_TOUCH
+  #define M43_NEVER_TOUCH(Q) ((Q) == 29 || (Q) == 30 || (Q) == 73)  // USB pins
+#endif
+
 // active ADC function/mode/code values for PINSEL registers
 constexpr int8_t ADC_pin_mode(pin_t pin) {
   return (LPC1768_PIN_PORT(pin) == 0 && LPC1768_PIN_PIN(pin) == 2  ? 2 :
diff --git a/Marlin/src/gcode/config/M43.cpp b/Marlin/src/gcode/config/M43.cpp
index 5965f48b77..e1445eaf6d 100644
--- a/Marlin/src/gcode/config/M43.cpp
+++ b/Marlin/src/gcode/config/M43.cpp
@@ -47,13 +47,13 @@ inline void toggle_pins() {
 
   for (uint8_t i = start; i <= end; i++) {
     pin_t pin = GET_PIN_MAP_PIN(i);
-    //report_pin_state_extended(pin, ignore_protection, false);
     if (!VALID_PIN(pin)) continue;
-    if (!ignore_protection && pin_is_protected(pin)) {
+    if (M43_NEVER_TOUCH(i) || (!ignore_protection && pin_is_protected(pin))) {
       report_pin_state_extended(pin, ignore_protection, true, "Untouched ");
       SERIAL_EOL();
     }
     else {
+      watchdog_reset();
       report_pin_state_extended(pin, ignore_protection, true, "Pulsing   ");
       #if AVR_AT90USB1286_FAMILY // Teensy IDEs don't know about these pins so must use FASTIO
         if (pin == TEENSY_E2) {
@@ -77,12 +77,12 @@ inline void toggle_pins() {
       {
         pinMode(pin, OUTPUT);
         for (int16_t j = 0; j < repeat; j++) {
-          extDigitalWrite(pin, 0); safe_delay(wait);
-          extDigitalWrite(pin, 1); safe_delay(wait);
-          extDigitalWrite(pin, 0); safe_delay(wait);
+          watchdog_reset(); extDigitalWrite(pin, 0); safe_delay(wait);
+          watchdog_reset(); extDigitalWrite(pin, 1); safe_delay(wait);
+          watchdog_reset(); extDigitalWrite(pin, 0); safe_delay(wait);
+          watchdog_reset();
         }
       }
-
     }
     SERIAL_EOL();
   }
@@ -277,7 +277,7 @@ void GcodeSuite::M43() {
     for (uint8_t i = first_pin; i <= last_pin; i++) {
       pin_t pin = GET_PIN_MAP_PIN(i);
       if (!VALID_PIN(pin)) continue;
-      if (!ignore_protection && pin_is_protected(pin)) continue;
+      if (M43_NEVER_TOUCH(i) || (!ignore_protection && pin_is_protected(pin))) continue;
       pinMode(pin, INPUT_PULLUP);
       delay(1);
       /*
@@ -300,7 +300,7 @@ void GcodeSuite::M43() {
       for (uint8_t i = first_pin; i <= last_pin; i++) {
         pin_t pin = GET_PIN_MAP_PIN(i);
         if (!VALID_PIN(pin)) continue;
-        if (!ignore_protection && pin_is_protected(pin)) continue;
+        if (M43_NEVER_TOUCH(i) || (!ignore_protection && pin_is_protected(pin))) continue;
         const byte val =
           /*
             IS_ANALOG(pin)
diff --git a/Marlin/src/pins/pinsDebug.h b/Marlin/src/pins/pinsDebug.h
index a8003fcd97..2cf896abbb 100644
--- a/Marlin/src/pins/pinsDebug.h
+++ b/Marlin/src/pins/pinsDebug.h
@@ -102,6 +102,9 @@ const PinInfo pin_array[] PROGMEM = {
 
 #include HAL_PATH(../HAL, pinsDebug.h)  // get the correct support file for this CPU
 
+#ifndef M43_NEVER_TOUCH
+  #define M43_NEVER_TOUCH(Q) false
+#endif
 
 static void print_input_or_output(const bool isout) {
   serialprintPGM(isout ? PSTR("Output = ") : PSTR("Input  = "));