diff --git a/nmcli-with-gsm.md b/nmcli-with-gsm.md
index fa02ab4..928bbc5 100644
--- a/nmcli-with-gsm.md
+++ b/nmcli-with-gsm.md
@@ -201,3 +201,12 @@ sudo gpio write 15 1
 sleep 5
 sudo gpio write 15 0
 ```
+# Enable ModemManager debug
+change /etc/systemd/system/dbus-org.freedesktop.ModemManager1.service
+add --debug after `/usr/sbin/ModemManager`
+then  
+```
+sudo systemctl daemon-reload
+sudo systemctl restart  ModemManager.service  
+```
+