diff --git a/opendbc/car/nissan/carcontroller.py b/opendbc/car/nissan/carcontroller.py
index 42f693a2b16..ad0717267c6 100644
--- a/opendbc/car/nissan/carcontroller.py
+++ b/opendbc/car/nissan/carcontroller.py
@@ -22,6 +22,7 @@ def __init__(self, dbc_names, CP):
     self.packer = CANPacker(dbc_names[Bus.pt])
 
   def update(self, CC, CS, now_nanos):
+    raise RuntimeError("car_diff error dropdown test")  # TODO: remove, intentional failure to exercise car_diff error reporting
     actuators = CC.actuators
     hud_control = CC.hudControl
     pcm_cancel_cmd = CC.cruiseControl.cancel
diff --git a/opendbc/car/tests/car_diff.py b/opendbc/car/tests/car_diff.py
index b4424be8975..37d82314056 100755
--- a/opendbc/car/tests/car_diff.py
+++ b/opendbc/car/tests/car_diff.py
@@ -293,8 +293,11 @@ def main(platform: str | None = None, segments_per_platform: int = 10, update_re
   icon = "⚠️" if with_diffs else "✅"
   print(f"\n{icon}  {len(with_diffs)} changed, {n_passed} passed, {len(errors)} errors")
 
-  for plat, seg, err in errors:
-    print(f"\nERROR {plat} - {seg}: {err}")
+  if errors:
+    print("<details><summary><b>Show errors</b></summary>\n\n```")
+    for err in dict.fromkeys(err for _, _, err in errors):
+      print(f"\n{err}")
+    print("```\n</details>")
 
   if with_diffs:
     print("<details><summary><b>Show changes</b></summary>\n\n```")