diff --git a/APMrover2/APM_Config.h b/APMrover2/APM_Config.h
index 81269d6157..3813a45142 100644
--- a/APMrover2/APM_Config.h
+++ b/APMrover2/APM_Config.h
@@ -20,10 +20,6 @@
 
 #define TRACE               DISABLED
 
-// sonar is currently broken - it causes an APM1 to crash
-// after a few seconds
-#define CONFIG_SONAR DISABLED
-
 //#define LOGGING_ENABLED DISABLED
 
 //#include "APM_Config_HILmode.h"  // for test in HIL mode with AeroSIM Rc 3.83
diff --git a/APMrover2/system.pde b/APMrover2/system.pde
index 13ee2eac13..23e46136ca 100644
--- a/APMrover2/system.pde
+++ b/APMrover2/system.pde
@@ -129,6 +129,9 @@ static void init_ardupilot()
 
     timer_scheduler.init( & isr_registry );
 
+    // initialise the analog port reader
+    AP_AnalogSource_Arduino::init_timer(&timer_scheduler);
+
 	//
 	// Check the EEPROM format version before loading any parameters from EEPROM.
 	//