diff --git a/libraries/AP_NavEKF3/AP_NavEKF3.cpp b/libraries/AP_NavEKF3/AP_NavEKF3.cpp
index 41038740c2..915f78c311 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3.cpp
+++ b/libraries/AP_NavEKF3/AP_NavEKF3.cpp
@@ -1030,13 +1030,21 @@ bool NavEKF3::healthy(void) const
     return core[primary].healthy();
 }
 
-bool NavEKF3::all_cores_healthy(void) const
+// returns false if we fail arming checks, in which case the buffer will be populated with a failure message
+bool NavEKF3::pre_arm_check(char *failure_msg, uint8_t failure_msg_len) const
 {
     if (!core) {
+        hal.util->snprintf(failure_msg, failure_msg_len, "no EKF3 cores");
         return false;
     }
     for (uint8_t i = 0; i < num_cores; i++) {
         if (!core[i].healthy()) {
+            const char *failure = core[primary].prearm_failure_reason();
+            if (failure != nullptr) {
+                hal.util->snprintf(failure_msg, failure_msg_len, failure);
+            } else {
+                hal.util->snprintf(failure_msg, failure_msg_len, "EKF3 core %d unhealthy", (int)i);
+            }
             return false;
         }
     }
@@ -1796,21 +1804,6 @@ uint32_t NavEKF3::getLastVelNorthEastReset(Vector2f &vel) const
     return core[primary].getLastVelNorthEastReset(vel);
 }
 
-// report the reason for why the backend is refusing to initialise
-const char *NavEKF3::prearm_failure_reason(void) const
-{
-    if (!core) {
-        return "no EKF3 cores";
-    }
-    for (uint8_t i = 0; i < num_cores; i++) {
-        const char * failure = core[primary].prearm_failure_reason();
-        if (failure != nullptr) {
-            return failure;
-        }
-    }
-    return nullptr;
-}
-
 // Returns the amount of vertical position change due to the last reset or core switch in metres
 // Returns the time of the last reset or 0 if no reset or core switch has ever occurred
 // Where there are multiple consumers, they must access this function on the same frame as each other
diff --git a/libraries/AP_NavEKF3/AP_NavEKF3.h b/libraries/AP_NavEKF3/AP_NavEKF3.h
index cc77ed4e8a..e09ce64ef6 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3.h
+++ b/libraries/AP_NavEKF3/AP_NavEKF3.h
@@ -59,8 +59,8 @@ public:
     // Check basic filter health metrics and return a consolidated health status
     bool healthy(void) const;
 
-    // Check that all cores are started and healthy
-    bool all_cores_healthy(void) const;
+    // returns false if we fail arming checks, in which case the buffer will be populated with a failure message
+    bool pre_arm_check(char *failure_msg, uint8_t failure_msg_len) const;
 
     // Update instance error scores for all available cores 
     float updateCoreErrorScores(void);
@@ -398,9 +398,6 @@ public:
     // returns the time of the last reset or 0 if no reset has ever occurred
     uint32_t getLastPosDownReset(float &posDelta);
 
-    // report any reason for why the backend is refusing to initialise
-    const char *prearm_failure_reason(void) const;
-
     // set and save the _baroAltNoise parameter
     void set_baro_alt_noise(float noise) { _baroAltNoise.set_and_save(noise); };
 
diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_VehicleStatus.cpp b/libraries/AP_NavEKF3/AP_NavEKF3_VehicleStatus.cpp
index a5a693fa2f..9954ea10cc 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_VehicleStatus.cpp
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_VehicleStatus.cpp
@@ -13,7 +13,7 @@ extern const AP_HAL::HAL& hal;
    Monitor magnetometer innovations to see if the heading is good enough to use GPS
    Return true if all criteria pass for 10 seconds
 
-   We also record the failure reason so that prearm_failure_reason()
+   We also record the failure reason so that pre_arm_check()
    can give a good report to the user on why arming is failing
 */
 void NavEKF3_core::calcGpsGoodToAlign(void)