diff --git a/selfdrive/test/process_replay/card_diff.py b/selfdrive/test/process_replay/card_diff.py
new file mode 100644
index 00000000000000..39f471d4168e32
--- /dev/null
+++ b/selfdrive/test/process_replay/card_diff.py
@@ -0,0 +1,76 @@
+#!/usr/bin/env python3
+import argparse
+import pickle
+import sys
+from collections import Counter, defaultdict
+from pathlib import Path
+
+from openpilot.tools.lib.logreader import LogReader
+from openpilot.selfdrive.test.process_replay.process_replay import (
+  replay_process, get_process_config, check_openpilot_enabled,
+)
+from openpilot.selfdrive.test.process_replay.compare_logs import (
+  compare_logs, format_process_diff,
+)
+from opendbc.car.tests.car_diff import dict_diff, format_diff, IGNORE_FIELDS, TOLERANCE
+
+CARD_CFG = get_process_config("card")
+
+
+def run_card(route):
+  lr = list(LogReader(route))
+  if not check_openpilot_enabled(lr):
+    print(f"Warning: {route} never engaged")
+  return replay_process(CARD_CFG, lr)
+
+
+def main():
+  parser = argparse.ArgumentParser()
+  parser.add_argument("route")
+  parser.add_argument("--ref", help="Reference route or .pkl file")
+  parser.add_argument("--save", help="Save to .pkl")
+  args = parser.parse_args()
+
+  print(f"Replaying: {args.route}")
+  new = run_card(args.route)
+  print(f"Got {len(new)} msgs: {dict(Counter(m.which() for m in new))}")
+
+  if args.save:
+    Path(args.save).write_bytes(pickle.dumps(new))
+    print(f"Saved: {args.save}")
+    return 0
+
+  if not args.ref:
+    print("Use --ref to compare or --save to save")
+    return 0
+
+  ref = pickle.loads(Path(args.ref).read_bytes()) if args.ref.endswith(".pkl") else run_card(args.ref)
+
+  diffs = compare_logs(ref, new, ignore_fields=CARD_CFG.ignore, tolerance=CARD_CFG.tolerance)
+
+  if not diffs:
+    print("PASS: no diffs")
+    return 0
+
+  diff, _ = format_process_diff(diffs)
+  print(f"\n{len(diffs)} diffs:")
+  print(diff)
+
+  ref_states = [(m.logMonoTime, m.carState) for m in ref if m.which() == "carState"]
+  new_states = [m.carState for m in new if m.which() == "carState"]
+
+  by_field = defaultdict(list)
+  for i, ((ts, r), n) in enumerate(zip(ref_states, new_states)):
+    for d in dict_diff(r.to_dict(), n.to_dict(), ignore=IGNORE_FIELDS, tolerance=TOLERANCE):
+      by_field[d[1]].append((d[1], i, d[2], ts))
+
+  for field, fd in sorted(by_field.items()):
+    print(f"  {field} ({len(fd)} diffs)")
+    for line in format_diff(fd, ref_states, new_states, field):
+      print(line)
+
+  return 1
+
+
+if __name__ == "__main__":
+  sys.exit(main())