Tools · BACnet Error Code Decoder

BACnet Error Code Decoder BACnet

Turn the numbers a device sends back when it refuses a request into what actually went wrong — error class and code, reject reason, or abort reason.

When a BACnet request fails, the device answers with one of three things: a BACnet-Error (an error class plus an error code), a BACnet-Reject (a reject reason — the message was malformed), or a BACnet-Abort (an abort reason — the transaction was torn down). Pick the kind you got, type the number(s), and read the meaning; or filter the full reference tables below.

The inputs are seeded with an example — edit them to your numbers.

Input

Error class (0–7)

Error code (0–255)

An Error is a class + code pair — the service ran and the device refused it.

Output

Error code —

Error class —

Enter a value to decode it.

The full reference

Every error class, error code, reject reason, and abort reason, filterable across all four at once. Click a value to copy it.

Filter by number, name, or meaning

Code	Name	What it means
0	other	Catch-all the device returns when no specific code fits; the real cause is vendor-defined, so check the device's own log or manual.
1	authentication-failed	—
2	configuration-in-progress	Device is mid-download or commissioning and can't service the request; retry once the config or program load finishes.
3	device-busy	Device is temporarily overloaded, often mid-backup, restore, or program load; back off and retry in a few seconds.
4	dynamic-creation-not-supported	—
5	file-access-denied	File-object read or write refused; usually a permissions issue or the file is locked open by a backup or restore.
6	incompatible-security-levels	—
7	inconsistent-parameters	Service arguments conflict with each other, like a mismatched array size or bad option combo; fix the request the tool built.
8	inconsistent-selection-criterion	—
9	invalid-data-type	Written value's datatype doesn't match the property, such as a real into an enum or integer; correct the datatype in the write.
10	invalid-file-access-method	—
11	invalid-file-start-position	—
12	invalid-operator-name	—
13	invalid-parameter-data-type	—
14	invalid-time-stamp	—
15	key-generation-error	—
16	missing-required-parameter	The request PDU left out a mandatory field; a malformed client request, so check the tool or driver encoding.
17	no-objects-of-specified-type	—
18	no-space-for-object	Device's object database is full, so CreateObject fails; delete unused objects or you've hit the device's object limit.
19	no-space-to-add-list-element	—
20	no-space-to-write-property	Property storage is full, often when adding to a list like a schedule or group; free space or trim existing entries.
21	no-vt-sessions-available	—
22	property-is-not-a-list	AddListElement or RemoveListElement was used on a property that isn't a list; wrong service for that property.
23	object-deletion-not-permitted	Object can't be deleted because it's built-in, like the Device object or a fixed I/O point; only dynamic objects delete.
24	object-identifier-already-exists	CreateObject asked for an instance number already in use; pick an unused instance for that object type.
25	operational-problem	Device has an internal fault blocking the operation; check its health and alarms, and it may need a reboot.
26	password-failure	—
27	read-access-denied	The property exists but reading it is blocked; you lack the rights or security level to read that property.
28	security-not-supported	—
29	service-request-denied	The target device refused the service on its own policy, state, or security grounds; the request was well-formed, so check that device, not the network.
30	timeout	No reply within the APDU timeout; a comms problem like wrong MAC or network number, a dead device, or MS/TP token loss.
31	unknown-object	The referenced object doesn't exist on the device; wrong object type or instance, or it was deleted — a rename won't do it, references are by id.
32	unknown-property	The object doesn't support that property id; wrong property or a proprietary one this device doesn't implement.
34	unknown-vt-class	—
35	unknown-vt-session	—
36	unsupported-object-type	CreateObject asked for an object type the device doesn't implement; check the PICS for supported types.
37	value-out-of-range	Written value is outside the property's allowed range, like a bad priority, COV increment, or setpoint; clamp it to range.
38	vt-session-already-closed	—
39	vt-session-termination-failure	—
40	write-access-denied	Property is read-only or not writable now, such as an input's Present_Value or a command-priority conflict.
41	character-set-not-supported	—
42	invalid-array-index	Array index is past the property's size, or index 0 misused; read the array length before indexing into it.
43	cov-subscription-failed	Device couldn't set up the COV subscription, usually its subscription table is full; free a slot or fall back to polling.
44	not-cov-property	Subscribed change-of-value on a property that doesn't support it; only ones like Present_Value or Status_Flags qualify.
45	optional-functionality-not-supported	Device doesn't implement that optional service or feature; check its BIBBs or PICS before relying on it.
46	invalid-configuration-data	—
47	datatype-not-supported	The datatype used isn't one the device accepts for that property or operation; re-encode with a supported type.
48	duplicate-name	The Object_Name is already taken on this device; names must be unique per device, so choose another.
49	duplicate-object-id	The object-identifier collides with an existing object; that instance is already assigned on the device.
50	property-is-not-an-array	An array index was used on a scalar property; drop the index and read or write the value whole.
51	abort-buffer-overflow	—
52	abort-invalid-apdu-in-this-state	—
53	abort-preempted-by-higher-priority-task	—
54	abort-segmentation-not-supported	—
56	abort-other	—
57	invalid-tag	—
58	network-down	—
59	reject-buffer-overflow	—
60	reject-inconsistent-parameters	—
61	reject-invalid-parameter-data-type	—
62	reject-invalid-tag	—
63	reject-missing-required-parameter	—
64	reject-parameter-out-of-range	—
65	reject-too-many-arguments	—
66	reject-undefined-enumeration	—
67	reject-unrecognized-service	—
69	reject-other	—
70	unknown-device	A responding gateway or proxy doesn't recognize the referenced device instance; a true dead route instead shows up as a network Reject or a timeout, not this.
71	unknown-route	—
72	value-not-initialized	Property holds no value yet, typically an empty priority-array slot or a point that was never written.
73	invalid-event-state	—
74	no-alarm-configured	—
75	log-buffer-full	—
76	logged-value-purged	—
77	no-property-specified	—
78	not-configured-for-triggered-logging	—
79	unknown-subscription	Referenced a COV subscription that no longer exists; it expired or was never created, so resubscribe.
80	parameter-out-of-range	—
81	list-element-not-found	—
82	busy	Device can't service the request at the moment; wait briefly and retry.
83	communication-disabled	DeviceCommunicationControl has silenced the device's traffic; send a DCC enable or wait out its timer to restore comms.
84	success	No error; the positive result code confirming the operation completed.
85	access-denied	Request refused on authorization grounds; you lack the rights, common with BACnet/SC or key-based security.
86	bad-destination-address	—
87	bad-destination-device-id	—
88	bad-signature	—
89	bad-source-address	—
90	bad-timestamp	—
91	cannot-use-key	—
92	cannot-verify-message-id	—
93	correct-key-revision	—
94	destination-device-id-required	—
95	duplicate-message	—
96	encryption-not-configured	—
97	encryption-required	—
98	incorrect-key	—
99	invalid-key-data	—
100	key-update-in-progress	—
101	malformed-message	—
102	not-key-server	—
103	security-not-configured	—
104	source-security-required	—
105	too-many-keys	—
106	unknown-authentication-type	—
107	unknown-key	—
108	unknown-key-revision	—
109	unknown-source-message	—
110	not-router-to-dnet	—
111	router-busy	—
112	unknown-network-message	—
113	message-too-long	—
114	security-error	—
115	addressing-error	—
116	write-bdt-failed	—
117	read-bdt-failed	—
118	register-foreign-device-failed	—
119	read-fdt-failed	—
120	delete-fdt-entry-failed	—
121	distribute-broadcast-failed	—
122	unknown-file-size	—
123	abort-apdu-too-long	—
124	abort-application-exceeded-reply-time	—
125	abort-out-of-resources	—
126	abort-tsm-timeout	—
127	abort-window-size-out-of-range	—
128	file-full	—
129	inconsistent-configuration	—
130	inconsistent-object-type	—
131	internal-error	—
132	not-configured	—
133	out-of-memory	—
134	value-too-long	—
135	abort-insufficient-security	—
136	abort-security-error	—
137	duplicate-entry	—
138	invalid-value-in-this-state	—
139	invalid-operation-in-this-state	—
140	list-item-not-numbered	—
141	list-item-not-timestamped	—
142	invalid-data-encoding	—
143	bvlc-function-unknown	—
145	header-encoding-error	—
146	header-not-understood	—
147	message-incomplete	—
148	not-a-bacnet-sc-hub	—
149	payload-expected	—
150	unexpected-data	—
151	node-duplicate-vmac	—
152	http-unexpected-response-code	—
153	http-no-upgrade	—
154	http-resource-not-local	—
155	http-proxy-authentication-failed	—
156	http-response-timeout	—
157	http-response-syntax-error	—
158	http-response-value-error	—
159	http-response-missing-header	—
160	http-websocket-header-error	—
161	http-upgrade-required	—
162	http-upgrade-error	—
163	http-temporary-unavailable	—
164	http-not-a-server	—
165	http-error	—
166	websocket-scheme-not-supported	—
167	websocket-unknown-control-message	—
168	websocket-close-error	—
169	websocket-closed-by-peer	—
170	websocket-endpoint-leaves	—
171	websocket-protocol-error	—
172	websocket-data-not-accepted	—
173	websocket-closed-abnormally	—
174	websocket-data-inconsistent	—
175	websocket-data-against-policy	—
176	websocket-frame-too-long	—
177	websocket-extension-missing	—
178	websocket-request-unavailable	—
179	websocket-error	—
180	tls-client-certificate-error	—
181	tls-server-certificate-error	—
182	tls-client-authentication-failed	—
183	tls-server-authentication-failed	—
184	tls-client-certificate-expired	—
185	tls-server-certificate-expired	—
186	tls-client-certificate-revoked	—
187	tls-server-certificate-revoked	—
188	tls-error	—
189	dns-unavailable	—
190	dns-name-resolution-failed	—
191	dns-resolver-failure	—
192	dns-error	—
193	tcp-connect-timeout	—
194	tcp-connection-refused	—
195	tcp-closed-by-local	—
196	tcp-closed-other	—
197	tcp-error	—
198	ip-address-not-reachable	—
199	ip-error	—
200	certificate-expired	—
201	certificate-invalid	—
202	certificate-malformed	—
203	certificate-revoked	—
204	unknown-security-key	—
205	referenced-port-in-error	—
206	not-enabled	—
207	adjust-scope-required	—
208	auth-scope-required	—
209	bind-scope-required	—
210	config-scope-required	—
211	control-scope-required	—
212	extended-scope-required	—
213	incorrect-client	—
214	install-scope-required	—
215	insufficient-scope	—
217	no-policy	—
218	revoked-token	—
219	override-scope-required	—
220	inactive-token	—
221	unknown-audience	—
222	unknown-client	—
223	unknown-scope	—
224	view-scope-required	—
225	incorrect-audience	—
226	incorrect-client-origin	—
227	invalid-array-size	—
228	incorrect-issuer	—
229	invalid-token	—
No codes match that filter.

Class	Name	What it means
0	device	Device-level refusal: it's busy, mid-configuration, or has an operational problem and cannot service the request; usually transient, so retry.
1	object	The target object is the problem: unknown-object (wrong instance number), wrong type, or a create or delete the device forbids; verify the object-id.
2	property	The addressed property is at fault: unknown-property, write-access-denied (read-only), value-out-of-range, or a wrong datatype or array index.
3	resources	Device is out of memory or space: no room to create the object, add a list element, or store the value; often a full points or objects table.
4	security	Security check failed: bad password, authentication failure, incompatible security levels, or a key or encryption error blocked the request.
5	services	The service request is malformed: missing or inconsistent parameters, invalid tag encoding, or a parameter out of range; usually a client or stack bug.
6	vt	Virtual Terminal session errors: unknown VT class or session, none available, or already closed; a legacy text-terminal feature you'll rarely see.
7	communication	Message-transport problems: comms disabled by DCC, a duplicate or incomplete message, or an unknown network or route; check DCC state and routing.
No classes match that filter.

Reason	Name	What it means
0	other	Catch-all reject for a parse-level rejection that fits none of the defined codes; grab the raw APDU with a sniffer to see what tripped it.
1	buffer-overflow	Request exceeded the receiver's decode buffer, so it couldn't be fully decoded and was rejected; usually an oversized APDU to a device with a small Max-APDU.
2	inconsistent-parameters	Each argument decoded fine but they contradict one another, so the request can't be honored; a combination the service won't accept together.
3	invalid-parameter-data-type	An argument's encoded type isn't what the service expects, like a Real where an Unsigned belongs; usually an encoder bug on the sender.
4	invalid-tag	A context or application tag is wrong or misplaced, so the decoder lost the byte stream; classic hand-rolled or buggy encoder symptom.
5	missing-required-parameter	A mandatory argument for the service wasn't present; the sender omitted a required field the decoder needs to proceed.
6	parameter-out-of-range	An argument decoded but its value sits outside the range that field allows, such as an index or choice beyond the service's limits.
7	too-many-arguments	The request carried more arguments than the service defines; extra trailing parameters the decoder didn't expect to find.
8	undefined-enumeration	An enumerated argument held a value not defined for that enum; often a newer or proprietary code the receiver can't map.
9	unrecognized-service	The PDU parsed but the device doesn't implement that service choice; the requested service simply isn't supported here.
10	invalid-data-encoding	The bytes decode but do not form a legal encoding for their datatype — malformed at the datatype level, not just a bad tag. A later-edition reason older stacks will not send.
No reject reasons match that filter.

Reason	Name	What it means
0	other	Catch-all when no listed reason fits; the device tore down the transaction without saying why, so a packet capture is your only lead.
1	buffer-overflow	Receiver ran out of buffer space mid-transaction, usually a segmented message too big for a small device to reassemble; cut APDU size or segment count.
2	invalid-apdu-in-this-state	A segment or ACK the state machine wasn't expecting — often a stale duplicate retransmit, or a client reusing an invoke ID before its prior transaction closed.
3	preempted-by-higher-priority-task	Device intentionally abandoned this lower-priority transaction for more urgent internal work like reinitialization; uncommon, and not a load or slot issue.
4	segmentation-not-supported	The reply won't fit one APDU and this device can't segment; ask for less — smaller ReadPropertyMultiple or ReadRange chunks.
5	security-error	A BACnet network-security check failed — bad signature, key mismatch, or replayed message; verify keys and time sync across the secured devices.
6	insufficient-security	Message came in below the security level this operation requires; the peer must sign or encrypt to the policy minimum before the device will proceed.
7	window-size-out-of-range	The proposed segmentation window size fell outside the legal 1 to 127, or beyond what this device accepts — a botched segment-ACK negotiation.
8	application-exceeded-reply-time	The application layer took too long to build the response and the transaction was torn down; slow backend, blocked point, or an overloaded controller.
9	out-of-resources	Device has no free state-machine slots, memory, or handles left to continue; common on small controllers under heavy polling — throttle or stagger polls.
10	tsm-timeout	Transaction state machine timed out waiting for the next segment or ACK; usually a dropped packet, an offline peer, or MS/TP token loss.
11	apdu-too-long	The APDU exceeds the receiver's Max APDU Length Accepted and can't be segmented; shrink the request or response, or enable segmentation.
No abort reasons match that filter.

Enumerations imported from bacnet-stack's error enums (the de-facto machine-readable form of the ASHRAE 135 error tables, which are paywalled) — retrieved 2026-07-12: 8 classes, 225 error codes, 11 reject reasons, 12 abort reasons. Descriptions cover the field-common values; the long tail (BACnet/SC transport, HTTP / TLS / DNS, OAuth-scope codes added in later editions) is listed name-only. Verify exact normative wording against the standard.

Error vs. Reject vs. Abort

All three are a "no," but they fail at different points, and the difference tells you where to look. A BACnet-Error means your request was well-formed and the service ran — the device understood exactly what you asked and refused it, so it hands back an error class (the category) and an error code (the specific reason). This is the common one: unknown-property, write-access-denied, value-out-of-range.

A BACnet-Reject means the request never got that far — the APDU was malformed, mis-encoded, or used a service the device does not implement, so it was thrown out at the protocol layer before the service ran. A BACnet-Abort means a transaction that had already started was torn down mid-flight — almost always segmentation, a TSM timeout, or the device running out of buffer or resources. Reject points at the message; Abort points at the transport or the device's capacity.

Reading an error class and code

A BACnet-Error always carries the pair. The class buckets the problem — device, object, property, resources, security, services, vt, or communication — and the code is the specific message inside that bucket. In practice the code is what you act on; the class just tells you which subsystem raised it. The same code number can legitimately appear under more than one class, so decode both.

Classes 0–63 and the standard code range are ASHRAE's; a class 64 or above is a vendor-proprietary error, and its meaning lives in that manufacturer's documentation — the Vendor ID lookup tells you whose. The Object Reference covers the object types and properties these errors refer to.

BACnet error decoding FAQ

What is the difference between a BACnet Error, Reject, and Abort?

All three say a request failed, but at different stages. An Error means the service ran and the device refused it — it returns an error class plus an error code (unknown-property, write-access-denied). A Reject means the request could not be serviced at the protocol layer — malformed, mis-encoded, or asking for a service the device does not implement — thrown out before the service ran, and it returns a reject reason. An Abort tears down a transaction already in progress, usually over segmentation, a timeout, or resources — it returns an abort reason.

What does BACnet error class 2 code 32 mean?

Error class 2 is property and code 32 is unknown-property — you asked for a property the object does not have. Check the property identifier; a common cause is reading an optional property a given device or object does not implement.

What is a BACnet abort with reason APDU-too-long?

The response would not fit in one APDU and the device cannot segment it (or segmentation was not negotiated). It shows up on a big ReadPropertyMultiple or an Object_List read — split the request into smaller reads, or enable segmentation on both ends.

Why do I get write-access-denied writing a BACnet point?

Error code 40, write-access-denied, means the property is read-only or write-protected to you — for example an input's Present_Value, or a property the device simply will not let you write. On a commandable object, writing Present_Value directly can be refused because its value is owned by the program or the priority array — write at a priority instead, or write the object that actually drives it.

Where do I see the raw BACnet error class and code?

A workstation usually shows the decoded text, but a discovery log, an integration error dialog, or a Wireshark decode of the BACnet-Error / Reject / Abort APDU shows the bare numbers. That is when you paste them here.

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