diff --git a/selfdrive/debug/can_print_changes.py b/selfdrive/debug/can_print_changes.py
index 4fa775ac1..caf001eea 100755
--- a/selfdrive/debug/can_print_changes.py
+++ b/selfdrive/debug/can_print_changes.py
@@ -1,46 +1,75 @@
 #!/usr/bin/env python3
+import argparse
 import binascii
-import sys
+import time
 from collections import defaultdict
 
 import cereal.messaging as messaging
-from common.realtime import sec_since_boot
+from tools.lib.logreader import logreader_from_route_or_segment
 
 
-def can_printer(bus=0):
-  """Collects messages and prints when a new bit transition is observed.
-  This is very useful to find signals based on user triggered actions, such as blinkers and seatbelt.
-  Leave the script running until no new transitions are seen, then perform the action."""
+def update(msgs, bus, low_to_high, high_to_low, quiet=False):
+  for x in msgs:
+    if x.which() != 'can':
+      continue
+
+    for y in x.can:
+      if y.src == bus:
+        i = int.from_bytes(y.dat, byteorder='big')
+
+        l_h = low_to_high[y.address]
+        h_l = high_to_low[y.address]
+
+        change = None
+        if (i | l_h) != l_h:
+          low_to_high[y.address] = i | l_h
+          change = "+"
+
+        if (~i | h_l) != h_l:
+          high_to_low[y.address] = ~i | h_l
+          change = "-"
+
+        if change and not quiet:
+          print(f"{time.monotonic():.2f}\t{hex(y.address)} ({y.address})\t{change}{binascii.hexlify(y.dat)}")
+
+
+def can_printer(bus=0, init_msgs=None, new_msgs=None):
   logcan = messaging.sub_sock('can')
 
   low_to_high = defaultdict(int)
   high_to_low = defaultdict(int)
 
-  while 1:
-    can_recv = messaging.drain_sock(logcan, wait_for_one=True)
-    for x in can_recv:
-      for y in x.can:
-        if y.src == bus:
-          i = int.from_bytes(y.dat, byteorder='big')
+  if init_msgs is not None:
+    update(init_msgs, bus, low_to_high, high_to_low, quiet=True)
 
-          l_h = low_to_high[y.address]
-          h_l = high_to_low[y.address]
+  if new_msgs is not None:
+    update(new_msgs, bus, low_to_high, high_to_low)
+  else:
+    # Live mode
+    while 1:
+      can_recv = messaging.drain_sock(logcan, wait_for_one=True)
+      update(can_recv, bus, low_to_high, high_to_low)
 
-          change = None
-          if (i | l_h) != l_h:
-            low_to_high[y.address] = i | l_h
-            change = "+"
 
-          if (~i | h_l) != h_l:
-            high_to_low[y.address] = ~i | h_l
-            change = "-"
+if __name__ == "__main__":
+  desc = """Collects messages and prints when a new bit transition is observed.
+  This is very useful to find signals based on user triggered actions, such as blinkers and seatbelt.
+  Leave the script running until no new transitions are seen, then perform the action."""
 
-          if change:
-            print(f"{sec_since_boot():.2f}\t{hex(y.address)} ({y.address})\t{change}{binascii.hexlify(y.dat)}")
+  parser = argparse.ArgumentParser(description=desc,
+                                   formatter_class=argparse.ArgumentDefaultsHelpFormatter)
 
+  parser.add_argument("--bus", type=int, help="CAN bus to print out", default=0)
 
-if __name__ == "__main__":
-  if len(sys.argv) > 1:
-    can_printer(int(sys.argv[1]))
-  else:
-    can_printer()
+  parser.add_argument("--init", type=str, help="Route or segment to initialize with")
+  parser.add_argument("--comp", type=str, help="Route or segment to compare against init")
+
+  args = parser.parse_args()
+
+  init_lr, new_lr = None, None
+  if args.init:
+    init_lr = logreader_from_route_or_segment(args.init)
+  if args.comp:
+    new_lr = logreader_from_route_or_segment(args.comp)
+
+  can_printer(args.bus, init_msgs=init_lr, new_msgs=new_lr)
diff --git a/tools/lib/logreader.py b/tools/lib/logreader.py
index c8d506b4b..5597a5ffd 100755
--- a/tools/lib/logreader.py
+++ b/tools/lib/logreader.py
@@ -5,8 +5,9 @@ import bz2
 import urllib.parse
 import capnp
 
-from tools.lib.filereader import FileReader
 from cereal import log as capnp_log
+from tools.lib.filereader import FileReader
+from tools.lib.route import Route, SegmentName
 
 # this is an iterator itself, and uses private variables from LogReader
 class MultiLogIterator:
@@ -99,6 +100,16 @@ class LogReader:
       else:
         yield ent
 
+
+def logreader_from_route_or_segment(r):
+  sn = SegmentName(r, allow_route_name=True)
+  route = Route(sn.route_name.canonical_name)
+  if sn.segment_num < 0:
+    return MultiLogIterator(route.log_paths())
+  else:
+    return LogReader(route.log_paths()[sn.segment_num])
+
+
 if __name__ == "__main__":
   import codecs
   # capnproto <= 0.8.0 throws errors converting byte data to string