#!/usr/bin/perl -w
use strict;

while (<DATA>)
{
   if (m|^\s*<DTC>| ... m|^\s*</DTC>|)
   {
      print;   
   }
}

__DATA__ 
...is your data consisting of the C program...

##</code><code>##

<DTC>
  <TroubleCode>1101</TroubleCode> 
  <ShortDescription>The reductant pump needs to run slower than expected to keep the pressure.</ShortDescription>  
  <Classification>FAULT</Classification> 
  <SelfHealing>No selfhealing</SelfHealing> 
  <Erasability>erasable</Erasability> 
  <RedetectedDegradation>No Degradation</RedetectedDegradation> 
  <WarningLamp>No Warning Lamp</WarningLamp> 
  <DirectDegradation>No Action</DirectDegradation> 
  <Order>PRIMARY</Order> 
   </DTC>

##</code><code>##

/*XML doc start
<DTC>
  <TroubleCode>1101</TroubleCode> 
  <Classification>FAULT</Classification> 
  <SelfHealing>No selfhealing</SelfHealing> 
  <Erasability>erasable</Erasability> 
</DTC>
XML doc end */

##</code><code>##

/*Perl doc start
=some heading in Perl POD
... lines
=some other heading tag in Perl POD
..... lines
=cut
Perl doc end */