diff --git a/tools/releasetools/add_img_to_target_files.py b/tools/releasetools/add_img_to_target_files.py
index 4fe10c6..a56c305 100644
--- a/tools/releasetools/add_img_to_target_files.py
+++ b/tools/releasetools/add_img_to_target_files.py
@@ -59,12 +59,11 @@
 import build_image
 import build_super_image
 import common
-import rangelib
-import sparse_img
 import verity_utils
 import ota_metadata_pb2
 
 from apex_utils import GetSystemApexInfoFromTargetFiles
+from common import AddCareMapForAbOta
 
 if sys.hexversion < 0x02070000:
   print("Python 2.7 or newer is required.", file=sys.stderr)
@@ -110,45 +109,6 @@
       common.ZipWrite(self._output_zip, self.name, self._zip_name)
 
 
-def GetCareMap(which, imgname):
-  """Returns the care_map string for the given partition.
-
-  Args:
-    which: The partition name, must be listed in PARTITIONS_WITH_CARE_MAP.
-    imgname: The filename of the image.
-
-  Returns:
-    (which, care_map_ranges): care_map_ranges is the raw string of the care_map
-    RangeSet; or None.
-  """
-  assert which in common.PARTITIONS_WITH_CARE_MAP
-
-  # which + "_image_size" contains the size that the actual filesystem image
-  # resides in, which is all that needs to be verified. The additional blocks in
-  # the image file contain verity metadata, by reading which would trigger
-  # invalid reads.
-  image_size = OPTIONS.info_dict.get(which + "_image_size")
-  if not image_size:
-    return None
-
-  image_blocks = int(image_size) // 4096 - 1
-  assert image_blocks > 0, "blocks for {} must be positive".format(which)
-
-  # For sparse images, we will only check the blocks that are listed in the care
-  # map, i.e. the ones with meaningful data.
-  if "extfs_sparse_flag" in OPTIONS.info_dict:
-    simg = sparse_img.SparseImage(imgname)
-    care_map_ranges = simg.care_map.intersect(
-        rangelib.RangeSet("0-{}".format(image_blocks)))
-
-  # Otherwise for non-sparse images, we read all the blocks in the filesystem
-  # image.
-  else:
-    care_map_ranges = rangelib.RangeSet("0-{}".format(image_blocks))
-
-  return [which, care_map_ranges.to_string_raw()]
-
-
 def AddSystem(output_zip, recovery_img=None, boot_img=None):
   """Turn the contents of SYSTEM into a system image and store it in
   output_zip. Returns the name of the system image file."""
@@ -644,72 +604,6 @@
     assert available, "Failed to find " + img_name
 
 
-def AddCareMapForAbOta(output_zip, ab_partitions, image_paths):
-  """Generates and adds care_map.pb for a/b partition that has care_map.
-
-  Args:
-    output_zip: The output zip file (needs to be already open), or None to
-        write care_map.pb to OPTIONS.input_tmp/.
-    ab_partitions: The list of A/B partitions.
-    image_paths: A map from the partition name to the image path.
-  """
-  care_map_list = []
-  for partition in ab_partitions:
-    partition = partition.strip()
-    if partition not in common.PARTITIONS_WITH_CARE_MAP:
-      continue
-
-    verity_block_device = "{}_verity_block_device".format(partition)
-    avb_hashtree_enable = "avb_{}_hashtree_enable".format(partition)
-    if (verity_block_device in OPTIONS.info_dict or
-        OPTIONS.info_dict.get(avb_hashtree_enable) == "true"):
-      image_path = image_paths[partition]
-      assert os.path.exists(image_path)
-
-      care_map = GetCareMap(partition, image_path)
-      if not care_map:
-        continue
-      care_map_list += care_map
-
-      # adds fingerprint field to the care_map
-      # TODO(xunchang) revisit the fingerprint calculation for care_map.
-      partition_props = OPTIONS.info_dict.get(partition + ".build.prop")
-      prop_name_list = ["ro.{}.build.fingerprint".format(partition),
-                        "ro.{}.build.thumbprint".format(partition)]
-
-      present_props = [x for x in prop_name_list if
-                       partition_props and partition_props.GetProp(x)]
-      if not present_props:
-        logger.warning("fingerprint is not present for partition %s", partition)
-        property_id, fingerprint = "unknown", "unknown"
-      else:
-        property_id = present_props[0]
-        fingerprint = partition_props.GetProp(property_id)
-      care_map_list += [property_id, fingerprint]
-
-  if not care_map_list:
-    return
-
-  # Converts the list into proto buf message by calling care_map_generator; and
-  # writes the result to a temp file.
-  temp_care_map_text = common.MakeTempFile(prefix="caremap_text-",
-                                           suffix=".txt")
-  with open(temp_care_map_text, 'w') as text_file:
-    text_file.write('\n'.join(care_map_list))
-
-  temp_care_map = common.MakeTempFile(prefix="caremap-", suffix=".pb")
-  care_map_gen_cmd = ["care_map_generator", temp_care_map_text, temp_care_map]
-  common.RunAndCheckOutput(care_map_gen_cmd)
-
-  care_map_path = "META/care_map.pb"
-  if output_zip and care_map_path not in output_zip.namelist():
-    common.ZipWrite(output_zip, temp_care_map, arcname=care_map_path)
-  else:
-    shutil.copy(temp_care_map, os.path.join(OPTIONS.input_tmp, care_map_path))
-    if output_zip:
-      OPTIONS.replace_updated_files_list.append(care_map_path)
-
-
 def AddPackRadioImages(output_zip, images):
   """Copies images listed in META/pack_radioimages.txt from RADIO/ to IMAGES/.
 
@@ -1050,7 +944,9 @@
 
     # Generate care_map.pb for ab_partitions, then write this file to
     # target_files package.
-    AddCareMapForAbOta(output_zip, ab_partitions, partitions)
+    output_care_map = os.path.join(OPTIONS.input_tmp, "META", "care_map.pb")
+    AddCareMapForAbOta(output_zip if output_zip else output_care_map,
+                       ab_partitions, partitions)
 
   # Radio images that need to be packed into IMAGES/, and product-img.zip.
   pack_radioimages_txt = os.path.join(
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index b6ed8a4..83425cc 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -41,6 +41,7 @@
 from hashlib import sha1, sha256
 
 import images
+import rangelib
 import sparse_img
 from blockimgdiff import BlockImageDiff
 
@@ -3759,3 +3760,124 @@
   except ExternalError as e:
     logger.warning('Unable to get boot image timestamp: %s', e)
     return None
+
+
+def GetCareMap(which, imgname):
+  """Returns the care_map string for the given partition.
+
+  Args:
+    which: The partition name, must be listed in PARTITIONS_WITH_CARE_MAP.
+    imgname: The filename of the image.
+
+  Returns:
+    (which, care_map_ranges): care_map_ranges is the raw string of the care_map
+    RangeSet; or None.
+  """
+  assert which in PARTITIONS_WITH_CARE_MAP
+
+  # which + "_image_size" contains the size that the actual filesystem image
+  # resides in, which is all that needs to be verified. The additional blocks in
+  # the image file contain verity metadata, by reading which would trigger
+  # invalid reads.
+  image_size = OPTIONS.info_dict.get(which + "_image_size")
+  if not image_size:
+    return None
+
+  image_blocks = int(image_size) // 4096 - 1
+  assert image_blocks > 0, "blocks for {} must be positive".format(which)
+
+  # For sparse images, we will only check the blocks that are listed in the care
+  # map, i.e. the ones with meaningful data.
+  if "extfs_sparse_flag" in OPTIONS.info_dict:
+    simg = sparse_img.SparseImage(imgname)
+    care_map_ranges = simg.care_map.intersect(
+        rangelib.RangeSet("0-{}".format(image_blocks)))
+
+  # Otherwise for non-sparse images, we read all the blocks in the filesystem
+  # image.
+  else:
+    care_map_ranges = rangelib.RangeSet("0-{}".format(image_blocks))
+
+  return [which, care_map_ranges.to_string_raw()]
+
+
+def AddCareMapForAbOta(output_file, ab_partitions, image_paths):
+  """Generates and adds care_map.pb for a/b partition that has care_map.
+
+  Args:
+    output_file: The output zip file (needs to be already open),
+        or file path to write care_map.pb.
+    ab_partitions: The list of A/B partitions.
+    image_paths: A map from the partition name to the image path.
+  """
+  if not output_file:
+    raise ExternalError('Expected output_file for AddCareMapForAbOta')
+
+  care_map_list = []
+  for partition in ab_partitions:
+    partition = partition.strip()
+    if partition not in PARTITIONS_WITH_CARE_MAP:
+      continue
+
+    verity_block_device = "{}_verity_block_device".format(partition)
+    avb_hashtree_enable = "avb_{}_hashtree_enable".format(partition)
+    if (verity_block_device in OPTIONS.info_dict or
+            OPTIONS.info_dict.get(avb_hashtree_enable) == "true"):
+      if partition not in image_paths:
+        logger.warning('Potential partition with care_map missing from images: %s',
+                       partition)
+        continue
+      image_path = image_paths[partition]
+      if not os.path.exists(image_path):
+        raise ExternalError('Expected image at path {}'.format(image_path))
+
+      care_map = GetCareMap(partition, image_path)
+      if not care_map:
+        continue
+      care_map_list += care_map
+
+      # adds fingerprint field to the care_map
+      # TODO(xunchang) revisit the fingerprint calculation for care_map.
+      partition_props = OPTIONS.info_dict.get(partition + ".build.prop")
+      prop_name_list = ["ro.{}.build.fingerprint".format(partition),
+                        "ro.{}.build.thumbprint".format(partition)]
+
+      present_props = [x for x in prop_name_list if
+                       partition_props and partition_props.GetProp(x)]
+      if not present_props:
+        logger.warning(
+            "fingerprint is not present for partition %s", partition)
+        property_id, fingerprint = "unknown", "unknown"
+      else:
+        property_id = present_props[0]
+        fingerprint = partition_props.GetProp(property_id)
+      care_map_list += [property_id, fingerprint]
+
+  if not care_map_list:
+    return
+
+  # Converts the list into proto buf message by calling care_map_generator; and
+  # writes the result to a temp file.
+  temp_care_map_text = MakeTempFile(prefix="caremap_text-",
+                                           suffix=".txt")
+  with open(temp_care_map_text, 'w') as text_file:
+    text_file.write('\n'.join(care_map_list))
+
+  temp_care_map = MakeTempFile(prefix="caremap-", suffix=".pb")
+  care_map_gen_cmd = ["care_map_generator", temp_care_map_text, temp_care_map]
+  RunAndCheckOutput(care_map_gen_cmd)
+
+  if not isinstance(output_file, zipfile.ZipFile):
+    shutil.copy(temp_care_map, output_file)
+    return
+  # output_file is a zip file
+  care_map_path = "META/care_map.pb"
+  if care_map_path in output_file.namelist():
+    # Copy the temp file into the OPTIONS.input_tmp dir and update the
+    # replace_updated_files_list used by add_img_to_target_files
+    if not OPTIONS.replace_updated_files_list:
+      OPTIONS.replace_updated_files_list = []
+    shutil.copy(temp_care_map, os.path.join(OPTIONS.input_tmp, care_map_path))
+    OPTIONS.replace_updated_files_list.append(care_map_path)
+  else:
+    ZipWrite(output_file, temp_care_map, arcname=care_map_path)
diff --git a/tools/releasetools/test_add_img_to_target_files.py b/tools/releasetools/test_add_img_to_target_files.py
index 6b7a7db..a5850d3 100644
--- a/tools/releasetools/test_add_img_to_target_files.py
+++ b/tools/releasetools/test_add_img_to_target_files.py
@@ -21,9 +21,10 @@
 import common
 import test_utils
 from add_img_to_target_files import (
-    AddCareMapForAbOta, AddPackRadioImages,
-    CheckAbOtaImages, GetCareMap)
+    AddPackRadioImages,
+    CheckAbOtaImages)
 from rangelib import RangeSet
+from common import AddCareMapForAbOta, GetCareMap
 
 
 OPTIONS = common.OPTIONS
@@ -174,9 +175,9 @@
   def test_AddCareMapForAbOta(self):
     image_paths = self._test_AddCareMapForAbOta()
 
-    AddCareMapForAbOta(None, ['system', 'vendor'], image_paths)
-
     care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.pb')
+    AddCareMapForAbOta(care_map_file, ['system', 'vendor'], image_paths)
+
     expected = ['system', RangeSet("0-5 10-15").to_string_raw(),
                 "ro.system.build.fingerprint",
                 "google/sailfish/12345:user/dev-keys",
@@ -191,10 +192,10 @@
     """Partitions without care_map should be ignored."""
     image_paths = self._test_AddCareMapForAbOta()
 
-    AddCareMapForAbOta(
-        None, ['boot', 'system', 'vendor', 'vbmeta'], image_paths)
-
     care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.pb')
+    AddCareMapForAbOta(
+        care_map_file, ['boot', 'system', 'vendor', 'vbmeta'], image_paths)
+
     expected = ['system', RangeSet("0-5 10-15").to_string_raw(),
                 "ro.system.build.fingerprint",
                 "google/sailfish/12345:user/dev-keys",
@@ -226,9 +227,9 @@
         ),
     }
 
-    AddCareMapForAbOta(None, ['system', 'vendor'], image_paths)
-
     care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.pb')
+    AddCareMapForAbOta(care_map_file, ['system', 'vendor'], image_paths)
+
     expected = ['system', RangeSet("0-5 10-15").to_string_raw(),
                 "ro.system.build.fingerprint",
                 "google/sailfish/12345:user/dev-keys",
@@ -250,9 +251,9 @@
         'vendor_verity_block_device': '/dev/block/vendor',
     }
 
-    AddCareMapForAbOta(None, ['system', 'vendor'], image_paths)
-
     care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.pb')
+    AddCareMapForAbOta(care_map_file, ['system', 'vendor'], image_paths)
+
     expected = ['system', RangeSet("0-5 10-15").to_string_raw(), "unknown",
                 "unknown", 'vendor', RangeSet("0-9").to_string_raw(), "unknown",
                 "unknown"]
@@ -281,9 +282,9 @@
         ),
     }
 
-    AddCareMapForAbOta(None, ['system', 'vendor'], image_paths)
-
     care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.pb')
+    AddCareMapForAbOta(care_map_file, ['system', 'vendor'], image_paths)
+
     expected = ['system', RangeSet("0-5 10-15").to_string_raw(),
                 "ro.system.build.thumbprint",
                 "google/sailfish/123:user/dev-keys",
@@ -300,9 +301,9 @@
     # Remove vendor_image_size to invalidate the care_map for vendor.img.
     del OPTIONS.info_dict['vendor_image_size']
 
-    AddCareMapForAbOta(None, ['system', 'vendor'], image_paths)
-
     care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.pb')
+    AddCareMapForAbOta(care_map_file, ['system', 'vendor'], image_paths)
+
     expected = ['system', RangeSet("0-5 10-15").to_string_raw(),
                 "ro.system.build.fingerprint",
                 "google/sailfish/12345:user/dev-keys"]
@@ -317,25 +318,26 @@
     del OPTIONS.info_dict['system_image_size']
     del OPTIONS.info_dict['vendor_image_size']
 
-    AddCareMapForAbOta(None, ['system', 'vendor'], image_paths)
+    care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.pb')
+    AddCareMapForAbOta(care_map_file, ['system', 'vendor'], image_paths)
 
-    self.assertFalse(
-        os.path.exists(os.path.join(OPTIONS.input_tmp, 'META', 'care_map.pb')))
+    self.assertFalse(os.path.exists(care_map_file))
 
   def test_AddCareMapForAbOta_verityNotEnabled(self):
     """No care_map.pb should be generated if verity not enabled."""
     image_paths = self._test_AddCareMapForAbOta()
     OPTIONS.info_dict = {}
-    AddCareMapForAbOta(None, ['system', 'vendor'], image_paths)
-
     care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.pb')
+    AddCareMapForAbOta(care_map_file, ['system', 'vendor'], image_paths)
+
     self.assertFalse(os.path.exists(care_map_file))
 
   def test_AddCareMapForAbOta_missingImageFile(self):
     """Missing image file should be considered fatal."""
     image_paths = self._test_AddCareMapForAbOta()
     image_paths['vendor'] = ''
-    self.assertRaises(AssertionError, AddCareMapForAbOta, None,
+    care_map_file = os.path.join(OPTIONS.input_tmp, 'META', 'care_map.pb')
+    self.assertRaises(common.ExternalError, AddCareMapForAbOta, care_map_file,
                       ['system', 'vendor'], image_paths)
 
   @test_utils.SkipIfExternalToolsUnavailable()