diff --git a/libraries/AP_RangeFinder/RangeFinder.cpp b/libraries/AP_RangeFinder/RangeFinder.cpp
index 5bb172898f..6951f6d8c4 100644
--- a/libraries/AP_RangeFinder/RangeFinder.cpp
+++ b/libraries/AP_RangeFinder/RangeFinder.cpp
@@ -582,7 +582,7 @@ void RangeFinder::update(void)
                 continue;
             }
             drivers[i]->update();
-            update_pre_arm_check(i);
+            drivers[i]->update_pre_arm_check();
         }
     }
 }
@@ -843,32 +843,6 @@ bool RangeFinder::pre_arm_check() const
     return true;
 }
 
-/*
-  set pre-arm checks to passed if the range finder has been exercised through a reasonable range of movement
-      max distance sensed is at least 50cm > min distance sensed
-      max distance < 200cm
-      min distance sensed is within 10cm of ground clearance or sensor's minimum distance
- */
-void RangeFinder::update_pre_arm_check(uint8_t instance)
-{
-    // return immediately if already passed or no sensor data
-    if (state[instance].pre_arm_check || state[instance].status == RangeFinder_NotConnected || state[instance].status == RangeFinder_NoData) {
-        return;
-    }
-
-    // update min, max captured distances
-    state[instance].pre_arm_distance_min = MIN(state[instance].distance_cm, state[instance].pre_arm_distance_min);
-    state[instance].pre_arm_distance_max = MAX(state[instance].distance_cm, state[instance].pre_arm_distance_max);
-
-    // Check that the range finder has been exercised through a realistic range of movement
-    if (((state[instance].pre_arm_distance_max - state[instance].pre_arm_distance_min) > RANGEFINDER_PREARM_REQUIRED_CHANGE_CM) &&
-         (state[instance].pre_arm_distance_max < RANGEFINDER_PREARM_ALT_MAX_CM) &&
-         ((int16_t)state[instance].pre_arm_distance_min < (MAX(state[instance].ground_clearance_cm,min_distance_cm(instance)) + 10)) &&
-         ((int16_t)state[instance].pre_arm_distance_min > (MIN(state[instance].ground_clearance_cm,min_distance_cm(instance)) - 10))) {
-        state[instance].pre_arm_check = true;
-    }
-}
-
 const Vector3f &RangeFinder::get_pos_offset_orient(enum Rotation orientation) const
 {
     uint8_t i=0;
diff --git a/libraries/AP_RangeFinder/RangeFinder.h b/libraries/AP_RangeFinder/RangeFinder.h
index 8903428eb6..56d9cf81f3 100644
--- a/libraries/AP_RangeFinder/RangeFinder.h
+++ b/libraries/AP_RangeFinder/RangeFinder.h
@@ -209,6 +209,5 @@ private:
     void detect_instance(uint8_t instance);
     void update_instance(uint8_t instance);  
 
-    void update_pre_arm_check(uint8_t instance);
     bool _add_backend(AP_RangeFinder_Backend *driver);
 };
diff --git a/libraries/AP_RangeFinder/RangeFinder_Backend.cpp b/libraries/AP_RangeFinder/RangeFinder_Backend.cpp
index f116a78bda..8de913780e 100644
--- a/libraries/AP_RangeFinder/RangeFinder_Backend.cpp
+++ b/libraries/AP_RangeFinder/RangeFinder_Backend.cpp
@@ -58,3 +58,29 @@ void AP_RangeFinder_Backend::set_status(RangeFinder::RangeFinder_Status status)
         state.range_valid_count = 0;
     }
 }
+
+/*
+  set pre-arm checks to passed if the range finder has been exercised through a reasonable range of movement
+      max distance sensed is at least 50cm > min distance sensed
+      max distance < 200cm
+      min distance sensed is within 10cm of ground clearance or sensor's minimum distance
+ */
+void AP_RangeFinder_Backend::update_pre_arm_check()
+{
+    // return immediately if already passed or no sensor data
+    if (state.pre_arm_check || state.status == RangeFinder::RangeFinder_NotConnected || state.status == RangeFinder::RangeFinder_NoData) {
+        return;
+    }
+
+    // update min, max captured distances
+    state.pre_arm_distance_min = MIN(state.distance_cm, state.pre_arm_distance_min);
+    state.pre_arm_distance_max = MAX(state.distance_cm, state.pre_arm_distance_max);
+
+    // Check that the range finder has been exercised through a realistic range of movement
+    if (((state.pre_arm_distance_max - state.pre_arm_distance_min) > RANGEFINDER_PREARM_REQUIRED_CHANGE_CM) &&
+         (state.pre_arm_distance_max < RANGEFINDER_PREARM_ALT_MAX_CM) &&
+         ((int16_t)state.pre_arm_distance_min < (MAX(state.ground_clearance_cm,state.min_distance_cm) + 10)) &&
+         ((int16_t)state.pre_arm_distance_min > (MIN(state.ground_clearance_cm,state.min_distance_cm) - 10))) {
+        state.pre_arm_check = true;
+    }
+}
diff --git a/libraries/AP_RangeFinder/RangeFinder_Backend.h b/libraries/AP_RangeFinder/RangeFinder_Backend.h
index 95b7ebc078..1b99b8c1d8 100644
--- a/libraries/AP_RangeFinder/RangeFinder_Backend.h
+++ b/libraries/AP_RangeFinder/RangeFinder_Backend.h
@@ -38,6 +38,8 @@ public:
 
     virtual void handle_msg(mavlink_message_t *msg) { return; }
 
+    void update_pre_arm_check();
+
 protected:
 
     // update status based on distance measurement