BAP reverse engineering (volkswagen PQ)

This is kind of a loose data collection on BAP (for the PQ plattform) collected from various data sources and reverse engineering.

VW uses BAP (German: “Bedien- und Anzeigeprotokoll” ~ control- and display protocol) for communication between a control unit and a display unit. BAP is meant to transport data event based instead of the usual broadcast style (e.g. ECU hot-lamp = bit X in message Y, broadcasted all 10ms). Instead data (e.g. data to be displayed or menus to be built in the telephone menu) is transmitted once and updated as necessary. BAP is the successor of DDP (Display Daten Protokoll ~ display data protocol).

Everything in Volkswagen-group terminology is German, so are some of the abbrevations.

The control unit generating the data to be displayed is called “FSG” (Funktionssteuergerät ~ functional control unit). No HMI / display capability.

The control unit displaying the data is called “ASG” (Anzeigesteuergerät ~ display control unit). In PQ this is either the cluster’s display (called MFA) or the radio-navigation unit (only for certain clima-related data). Usually displays data to the user / driver (HMI), able to display data from the FSG.

Communication is always between FSG and ASG. Not ASG to ASG and not FSG to FSG.

In general different control units have different CAN-IDs they emit data from. That is no different in BAP. Certain CAN-IDs are related to BAP-traffic. In vw terms, those messages will be called something like BAP_xxx (e.g. BAP_Clima, BAP_NAVI, BAP_Compass, …) depending on their function. This is the communication channel from FSG (clima control, navigation system, compass) to the ASG (display). The communication backwards (e.g. cluster confirming displaying of data or alive-status) also has its own CAN-IDs / messages (e.g. BAP_ASG_0x, BAP_Anzeige). The FSG sends a ‘request’ to the ASG which answers with a ‘indication’ and vice versa.

Terminology: OSI-Layer1: mostly CAN (could be LIN, FlexRay, MOST, …). OSI-Layer2-4: BCL (BAP communication layer), OSI-Layer5: BPL (BAP protocol layer), OSI-Layer6: BAL (BAP application layer), OSI-Layer7: application layer (BAP functions, e.g. display text, enable symbol, …).

Obviously nearly all data is routed from the different CAN-bus of the car (CAN-powertrain for PDC/PLA & old ACC, CAN-comfort, CAN-infotainment, CAN-extended) to the gateway which finally routes to CAN-cluster.

Despite its alive-functions (called ‘heartbeat’) data is only transmitted event-based or based on a request by FSG or ASG. No “unasked” transmissions take place.

A BAP-message can consist of multiple CAN-messages. Each BAP-message has a BAP-header which specifies lsg_id, fct_id and op_code in addition to the BAP-message’s data.


There are two types of BAP-messages: short (less or equal 6 BAP-data-bytes) or long (more than 6 BAP-data-bytes). DLC is variable.

  • the size of the BAP-header is always 2 bytes
  • BAP is big-endian (example: BAP-header is of size 16bit, e.g. using data[0] and data[1] of the CAN-message. Big-endian means that the MSB of the header is in byte0|bit7

BAP-payload-data (BAP-application-data <=6 (less or requal than 6 bytes) -> 1 CAN-message (dlc maximum = 8bytes) is enough to transmit all data. To indicate that it is a short-BAP-frame the MSB of the CAN-data[0] of the CAN-message must be clear (must NOT be set).

BAP short frame + example

If there is more than 6bytes of BAP-data to be transmitted, the BAP-message must be split into multiple CAN-messages. The first CAN-message of this BAP-message is special, since it announces the amount of data to be expected (BAP-preample) as well as the BAP-header. The following CAN-messages have a simple counter (BAP-index) plus the BAP-data. DLC is always according to needs.

BAP long frame
example of a long BAP-message

derived from:, see his python-class for a excellent python implementation

In the screenhot below you can see a decoded BAP-message which shows the radio station (“ANTENNE”) and the currently played song name (“Habitt” by “Laurell”) in the cluster’s main display, audio tab. Note that the screen is switched back and forth multiple times and only radio-BAP-information is shown in this CAN-trace which covers round about 30 seconds in total. That is why you see multiple occurences of the station-information. It is because data is always transmitted as soon as the audio-tab is opened.

CAN-messageCAN-ID (hex)comment
BAP_Anzeige_0267AhASG: RNS, Radio => FSG: OPS, HYB, Dämpfer
BAP_ASG_036C7hASG: RNS, Radio => FSG: Tel, TV, DSP
BAP_ASG_046CAhASG: RNS, Radio => FSG: RSE, Rearview
BAP_ASG_056CBhASG: RNS, Radio => FSG: Clima
BAP_ASG_066C6hASG: RNS, Radio => FSG: Tel., MDI
BAP_Clima6DBhFSG: Clima => ASG: RNS, Radio
BAP_RV6DChFSG: Rearview => ASG: RNS, Radio
BAP_Telefon_016D2hFSG: Tel. => ASG: RNS, Radio
BAP_Telefon_026D5hFSG: Tel. => ASG: RNS, Radio
BAP_Telefon_0363BhFSG: Tel. => ASG: RNS, Radio
list of known BAP-channels with corresponding CAN-ID

BAP communication

Inside the BAP system each control unit has (at least) one so called logical-ID “lsg_id” (logische Steuergeräte ID ~ logical control unit ID) which is partly derived from the CAN-message’s CAN-ID. Note that most control units have multiple lsg_ids, like telephone-menu and telephone-screen have different lsg_ids.

BAP_Charisma(*1)23 (0x17)
34 (0x22)
BAP_NAVI8 (0x8)
21 (0x15)
25 (0x19)
28 (0x1c)
35 (0x23)
50 (0x32)
BAP_AUDIOcluster shows RDS-information only, menu like structure only for FM radio stations49 (0x31)
BAP_SHZ(*1)3 (0x3)
BAP_Telefon_048 (0x8)
12 (0xc)
19 (0x13)
20 (0x14)
43 (0x2b)
BAP_RDKS(*1)4 (0x4)
7 (0x7)
8 (0x8)
12 (0xc)
BAP_ACC(*1)5 (0x5)
27 (0x1b)
BAP_OPS0 (0x0)
3 (0x3)
10 (0xa)
BAP_VZArecognized traffic signs in BAP-traffic33 (0x21)
BAP_LDW(*1)25 (0x19)
BAP_SWA(*1)26 (0x1a)
observed lsg_ids

*1 = menu items in cluster, at least no human readable content (like menu-item-textstrings) were observed in BAP-traffic from this unit

For each lsg_id exists a individual list of function-IDs “fct_id” (Funktions-ID ~ functional ID). These function-IDs describe functions that can be applied to the (sub-) control unit. For example: list all functions, screen-data, menu-data, … . For each lsg_id exists a special (device specific) set of fct_ids. However some fct_ids seem to be standardized in the BAP standard an thus often repeat:

0x01GetAllget all propertiesused to synchronize the application-cache in the ASG. FSG delivers all property-values with op_code ‘StatusAll’. Parameter ‘Data’ of op_code ‘StatusAll’ contains all function-property-values in one continously segmented BAP-message

op_code: GetAll (noParam), StatusAll (data), Error (errorCode)
0x02BAP-ConfigBAP_Version_major (byte), BAP_Version_minor (byte), LSG-Class (The LSG_Class_ID classifies the function catalogue uniquely because a function catalogue can occur several times with different LSG-IDs), LSG-Sub-Class, LSG-Version_major, LSG-Version_minorinformation for BAP-version and LSG-version

op_codes: Get (empty), Status (data), Reset (data), HeartbeatStatus (data),
Error (errorCode)
0x03Function-ListFctList = bitfield, bytestream,list of supported BAP-functions

This bitfield indicates the support of a certain function during runtime.

op_codes: Get (noParam), Status (FctList), HeartbeatStatus (FctList), Error (errorCode)
0x04HeartBeatHeartBeatTime (byte, scale=100, unit=ms, 0..25500ms)this message contains the time betweent two heartbeat-messages. The parameter ‘HeartBeatTime’ * 100ms = time in unit ‘milliseconds, ms’. If a heart beat error occurs for a BAP-connection, it is reported on function HeartBeat (0x04)

op_codes: Get (noParam), Status (HeartBeatTime), HeartbeatStatus (HeartBeatTime), Error (errorCode)
byte: 0x00=normalOperation, 0x01=offStandby, 0x02=reserved, 0x03=initializing, 0x04..0x0d=reserved,
0x0e=functionInactive, 0x0f=defective,
with the parameter ‘OP-State’ this function announces the operational state of the FSG

op_codes: Get (noParam), Status (OP_state), HeartbeatStatus (OP_state), Error (errorCode)

The op_code (operation code ID) indicates the type of operation which is to be applied to the “fct_id-lsg_id”-combination. This could be something like set-value, get-value, reset, …

op_codes are grouped in function classes. Each function class has its own values and valid op_codes.

Defined function classes:

  • Property: time independant value that can be read or written
  • Array: like property but for big amount of data (multiple elements at once, e.g. lists)
  • Method: time dependant action
  • Cache: synchronize application cache in ASG


The “Function List” (VW internal document) defines one function class (either Property or Array or Method or Cache) for each “ID” (most probable “ID” within the “Function List” means function ID = fct_id). As a result, each fct_id only has one function class and thus only one set of valid op_codes!

Function class
Function class
Function class
Function class
0Reset / SetSetArrayStartASG -> FSG (Start, Set)
FSG -> ASG (Reset)
1GetGetArrayAbortGetAllASG -> FSG
2SetGetSetGetArrayStartResultASG -> FSG
3HeartbeatStatusChangeArrayProcessingFSG -> ASG
4StatusStatusArrayResultStatusAllFSG -> ASG
5StatusAckFSG -> ASG
6AckASG -> FSG
7Error Error Error Error FSG -> ASG

Error codes: 0x00=noError, 0x01..0x3f=stdBAPerror, 0x40..0xff=reserved

VW requires:

  • All parameters transmitted via BAP shall be stored in non-volatile memory on the FSG to keep information during loss of power.
  • Function-IDs 1 to 4 shall not be evaluated by application if not otherwise specified

Note that each lsg_id has its own list of fct_ids and each fct_id has its own set of op_codes. Not all op_codes are valid for all fct_id! All named above are (hopefully) BAP-standardized, not any more device specific or at least the same over all BAP-participants.

Control & buttons

With displaying data, there is a need to control menus, select entries, manipulate values, etc. All this is handled by the FSG (and not via BAP). Button presses from the MFL (Multifunktionslenkrad ~ multifunctional steering wheel) or steering column stalks (up/down + OK/Reset at the wiper control stalk) are passed to the control unit (FSG) which then updates the ASG’s display. It is not entirely clear at the moment if the cluster (as main display device) also handles menus and propagates selected items or adjusted values to other control units (FSGs) (on request?).

For the multifunctional steering wheel CAN-message “mMFL_Tasten” transports the pressed button in byte[0] of CAN-message: CAN-ID 1473 (dec) = 0x5c1 (hex), cycle 100ms, dlc=4

Button codes are as follows for “normal” multifunctional steering wheel:

0x0A10menu up / MFA arrow right
0x099menu down / MFA arrow left
0x2234MFA up
0x2335MFA down
0x2840MFA OK / Reset (long press)
0x2941MFA back
0x022skip+ / right
0x033skip- / left
0x066volume +
0x077volume –
0x2A42PTT / Microphone / Voicecontrol

However some more modern PQ cars have a so called “MQB-style” multifunctional steering wheel with a completely different button layout. (These also have the GRA / cruise control switches) in steering-wheel-buttons and not in the turn-indicator-stalk or 3rd stalk). For those steering wheels, the button codes are different:

0x1016volume +
0x1117volume –
0x1521skip right +
0x1622skip left –

If no multifunctional steering wheel is present, the car has buttons on the right side of the wiper stalk. Those would be “up” / “down” and “OK” ( / Reset if long pressed) which also allow for navigation through the menus. It’s most probable, that those are routed with the message mLSM_1 (CAN-ID: 705 (dec) = 0x2c1(hex) in bit LS1_MFA_Tasten from SMLS into the system.

VW CAN and LIN (PQ plattform)

Note that the messaging scheme for PQ vs. MQB vs. MLB (Audi only) are entirely different. Following are the VW version definitions for the different CAN-matrix (as VW names its CAN-version).

  • PQ: CAN matrix v4.5.x (4.x ?)
  • MQB: CAN matrix v5.x
  • MLB: CAN matrix v6.x

CAN bus

VW uses 11bit identifiers in broadcast-manner, 29bit are used for diagnostic/ISO-traffic but that is (obviously) only seen when sniffing CAN bus during a diagnostic session.

Not all bus are present in all PQ cars. Passat B6 for example only has CAN powertrain + diagnosis. Passat B7 has powertrain, infotainment, comfort, cluster, infotainment mandatory.

CAN bus requires 120Ohm termination on either side of the distributed CAN. VW does use following terminations:

CANspeedtermination 1termination 2
AFS private100 kBit/sAFS: 66OhmAFS module left & right (both 2.6kOhm)
powertrain / Antrieb500 kBit/sECU / Motorsteuergerät: 66OhmACC (3C0-radars, LIDAR), AFS, Airbag, ESP/ABS, DCC, PDC/PLA, EPS/Lenkung, CAN-Gateway, TCU/Getriebe, LWS/Lenkwinkelsensor, GearSelector/Wählhebel, Haldex:
all 2.6kOhm
EPB (if not on private CAN with ABS)
diagnosis500 kBit/sCAN-Gateway: 66OhmOBD-II connector
infotainment100 kBit/sCIB/car interface box, CAN-Gateway, Radio&Navigation, phone, SHZ/Standheizung:
all 560Ohm
compass, MDI/mobile device interface, rearset audio, TV-Tuner, soundsystem:
all 5.6kOhm
cluster / Kombiinstrument500 kBit/sCAN-Gateway: 66Ohmcluster: 2.6kOhm
comfort100 kBit/sBCM, CAN-Gateway, clima: 560Ohm
driver-door, passenger-door: 1kOhm
trailer, Multifunktionssteuergerät, SMLS/steering column electronics, memory driver seat:
all 5.6kOhm
EPB private / parking break 500 kBit/sEPBABS/ESP (not MK60EC1)
SWA / side assist private500 kBit/sside assist masterside assist slave
extended500 kBit/s? CAN-Gateway ?
probably 66Ohm ?
MFK/multifunctional camera, SWA/side assist, ACC (post 3C0-radars like 3AA, 7N0)

“private” indicates a private CAN between control units. Private means that the CAN is not routed to the CAN-Gateway.

some abbreviations are more German than others:

  • AFS = Advanced Frontlight System
  • DCC = Dynamic Chassis Control
  • TCU = Transmission Control Unit = GSG = Getriebesteuergerät
  • LWS = Lenkwinkelsensor = steering angle sensor
  • BCM = Body Control Module = BSG = Bordnetzsteuergerät
  • SMLS = Schaltermodul Lenksäule = steering column electronics
  • EPS = Electronic Power Steering
  • SWA = Spurwechselassistent = lane change assist
  • EPB = Electronic Parking Brake = elektronische Parkbremse

LIN bus

speed 19,2 kBit/s

BCM-LIN / BSG-LINRLS/rain-&lightsensor, front wiper
Tür-LIN / doorback doors
SMLS-LIN / steering wheel electronicsMFL/MFSW multifunctional steering wheel
DWA-LIN / alarmalarm horn, sensors overhead (?)
Dach-LIN / roof

Higher level protocols


DDP (probably not used in PQ, clusters with red color dot matrix display)