diff --git a/lin.cpp b/lin.cpp
index ce5123a..79a6106 100644
--- a/lin.cpp
+++ b/lin.cpp
@@ -24,7 +24,6 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "Arduino.h"
 #include "lin.h"
-#include <util/delay.h>
 
  //void p(char *fmt, ... );
 
@@ -120,7 +119,8 @@ uint8_t Lin::addrParity(uint8_t addr)
 void Lin::send(uint8_t addr, const uint8_t* message, uint8_t nBytes,uint8_t proto)
 {
   uint8_t addrbyte = (addr&0x3f) | addrParity(addr);
-  uint8_t cksum = dataChecksum(message,nBytes,(proto==1) ? 0:addrbyte);
+  // LIN diagnostic frame shall always use CHKSUM of protocol version 1.x.
+  uint8_t cksum = dataChecksum(message, nBytes, (proto == 1 || addr == 0x3C) ? 0 : addrbyte);
   serialBreak();       // Generate the low signal that exceeds 1 char.
   serial.write(0x55);  // Sync byte
   serial.write(addrbyte);  // ID byte
@@ -143,26 +143,27 @@ uint8_t Lin::recv(uint8_t addr, uint8_t* message, uint8_t nBytes,uint8_t proto)
   pinMode(txPin, INPUT);
   digitalWrite(txPin, LOW);  // don't pull up
   do { // I hear myself
-    while(!serial.available()) { _delay_us(100); timeoutCount+= 100; if (timeoutCount>=timeout) goto done; }
+    while(!serial.available()) { delayMicroseconds(100); timeoutCount+= 100; if (timeoutCount>=timeout) goto done; }
   } while(serial.read() != 0x55);
   do {
-    while(!serial.available()) { _delay_us(100); timeoutCount+= 100; if (timeoutCount>=timeout) goto done; }
+    while(!serial.available()) { delayMicroseconds(100); timeoutCount+= 100; if (timeoutCount>=timeout) goto done; }
   } while(serial.read() != idByte);
 
 
   for (uint8_t i=0;i<nBytes;i++)
     {
       // This while loop strategy does not take into account the added time for the logic.  So the actual timeout will be slightly longer then written here.
-      while(!serial.available()) { _delay_us(100); timeoutCount+= 100; if (timeoutCount>=timeout) goto done; } 
+      while(!serial.available()) { delayMicroseconds(100); timeoutCount+= 100; if (timeoutCount>=timeout) goto done; } 
       message[i] = serial.read();
       bytesRcvd++;
     }
-  while(!serial.available()) { _delay_us(100); timeoutCount+= 100; if (timeoutCount>=timeout) goto done; }
+  while(!serial.available()) { delayMicroseconds(100); timeoutCount+= 100; if (timeoutCount>=timeout) goto done; }
   if (serial.available())
     {
     uint8_t cksum = serial.read();
     bytesRcvd++;
-    if (proto==1) idByte = 0;  // Don't cksum the ID byte in LIN 1.x
+    // LIN diagnostic frame shall always use CHKSUM of LIN protocol version 1.x.
+    if (proto == 1 || addr == 0x3D) idByte = 0; // Don't cksum the ID byte in LIN 1.x
     if (dataChecksum(message,nBytes,idByte) == cksum) bytesRcvd = 0xff;
     //p("cksum byte %x, calculated %x %x\n",cksum,dataChecksum(message,nBytes,idByte),dataChecksum(message,nBytes,0));
     }
diff --git a/lin.h b/lin.h
index aad89ef..761a969 100644
--- a/lin.h
+++ b/lin.h
@@ -22,6 +22,8 @@ ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
 
+#ifndef LIN_H_
+#define LIN_H_
 
 //typedef unsigned char uint8_t;
 //typedef unsigned int uint16_t;
@@ -124,3 +126,5 @@ class Lin
   void loop();
 
 };
+
+#endif // LIN_H_