diff --git a/pyghmi/ipmi/command.py b/pyghmi/ipmi/command.py
index 7e24dec2..b8028907 100644
--- a/pyghmi/ipmi/command.py
+++ b/pyghmi/ipmi/command.py
@@ -384,7 +384,7 @@ class Command(object):
             if 'error' in rsp:
                 if rsp['code'] == 203:  # Sensor does not exist, optional dev
                     continue
-                raise Exception(rsp['error'])
+                raise exc.IpmiException(rsp['error'], code=rsp['code'])
             yield self._sdr.sensors[sensor].decode_sensor_reading(rsp['data'])
 
     def get_sensor_descriptions(self):
diff --git a/pyghmi/ipmi/private/constants.py b/pyghmi/ipmi/private/constants.py
index 553a3097..98cbe909 100644
--- a/pyghmi/ipmi/private/constants.py
+++ b/pyghmi/ipmi/private/constants.py
@@ -1174,4 +1174,5 @@ ipmi_completion_codes = {
     0xd5: "Command not supported in present state",
     0xd6: "Cannot execute command because subfunction disabled or unavailable",
     0xff: "Unspecified",
+    0xffff: "Timeout",  # not ipmi, but used internally
 }
diff --git a/pyghmi/ipmi/private/session.py b/pyghmi/ipmi/private/session.py
index a4181036..b3940c3e 100644
--- a/pyghmi/ipmi/private/session.py
+++ b/pyghmi/ipmi/private/session.py
@@ -1436,7 +1436,7 @@ class Session(object):
         self.nowait = True
         self.timeout += 1
         if self.timeout > self.maxtimeout:
-            response = {'error': 'timeout'}
+            response = {'error': 'timeout', 'code': 0xffff}
             self.ipmicallback(response)
             self.nowait = False
             self._mark_broken()