Toyota training multiplexing networks

Controller Area Network CANEPS ECU Engine ECU ECM Air Conditioner Amplifier SIL DLC3 CAN-H CAN-L : CAN Main Bus Line High : CAN Sub-Bus Line High : CAN Main Bus Line Low : CAN Sub-Bus Li

• Additional Properties of MPX Protocols

Additional Properties of MPX Protocols

Protocol:A set of rules and standards for communication between networked

components Protocols establish the standards for a variety of possible network properties

Properties: Conventions

Communication Direction: One-way, two-wayTransmission Timing: Periodic, event-drivenCollision Detection & Recovery: Retransmission delay, priority scheme

Data Casting: Broadcast, unicast, multicastSleep Mode & Wake-up Function: Available, not available

The network protocols in Toyota vehicles include:

• BEAN

• CAN

• LIN

• AVC-LANEach protocol defines the rules and standards necessary for components on the network to communicate with one another Their rules and standards describe various network properties and their conventions

This section discusses some of these properties and typical conventions in more detail

Additional

Properties of MPX

Protocols

Main Body ECU

A/C ECU

Receiver Transmitter Data

Data

Communication direction is one of the considerations in multiplex network design Toyota networks may communicate in either a one-way direction or a two way direction

The directional design provides for two different situations:

In one-way communication, one component transmits data to another and waits for an acknowledgement In the example above, the Power Window ECU transmits data to the Main Body ECU that the power window switch is open The Main Body ECU only acknowledges receipt of the transmitted data

Two-way data transmissioninvolves data flowing in both directions – not just data and acknowledgement, but actual data in both directions In the example above, the Engine ECU transmits data related to the A/C compressor’s ON status and the A/C ECU acknowledges receipt of that data and replies with additional data related to the water and ambient temperature.BEAN communication direction can be either one-way or two-way The CAN, LIN, and AVC-LAN are all two-way communication networks

Communication

Direction

Page 86

Transmission Timing Periodic and event-driven

Meter ECU Water Temp

Sensor

Power Window Master Switch

Main Body ECU

Engine ECU

Main Body ECU

Meter ECU Power Window

Master Switch

W

Switch Operation

W S

Another network property taken into consideration in design is the

transmission timing of the data Data may be periodically transmitted or it may be event-driven.

Periodic data, such as a water temperature signal or engine speed, is transmitted at regular intervals Event-driven data is transmitted when an event occurs, such as when a switch is thrown

Transmission Timing

Collision Detection & RecoveryRetransmission delay or priority scheme

When two ECUs attempt to transmit data at the same time, a data collision occurs

Retransmission delay (BEAN)

Each ECU stops transmitting for a predetermined time interval ECUs resume

transmitting one after the other, with the highest priority ECU going first (10 kbps)

Priority scheme (CAN)

The ECU with the highest priority message is allowed to continue transmitting Other

ECUs stop until the communication line is no longer busy (250 to 500 kbps)

In a multi-master network (such as BEAN or CAN), collision detection is a

method of resolving data collisions that might occur when more than one ECU transmits at the same time Multiple access to the serial data bus allows individual ECUs to function independently and transmit at any time they sense

an idle network If a data collision occurs, the ECUs in some networks (such

as the BEAN) each wait for a slightly different predetermined time interval and then resume data transmission The sequence in which they restart is based

on their priority

CAN uses a message priority method for resolving conflicts on the network When a data collision occurs, the ECU with the highest priority message continues transmitting while the other ECUs stop The other ECUs can resume transmitting when they detect the communication line is not busy By not interrupting transmission of the priority message, the CAN protocol is able

to operate at faster speeds

Both LIN and AVC-LAN networks are controlled by a master node, so no collisions can occur and arbitration or collision management in the slave nodes is not required

Collision Detection

Data is sent from an ECU to a group of other ECUs.

Broadcast, unicast and multicast

Transmit Transmit

Transmit Receive Receive Receive Receive

Receive

Receive Receive

Another attribute of network protocol is data casting There are three basic types of data casting methods used

• Broadcast communication where every node on the network receives the

data

• Unicast communication where data is only addressed to one node on the

network and the address is ignored by the other nodes

• Multicast communication where data is transmitted from one node on the

network and addressed to a group of other nodes

The Body Electronics Area Network can transmit data using all three types of data casting methods

The Controller Area Network transmits using broadcast and multicast methods Individual ECUs can ignore sent data but will send a receipt of data transmission A CAN Bus Check is a broadcast signal which checks to confirm which ECUs are responding Replies are returned in the order of reception

Local Interconnect Network transmits using the multicast method

Audio Visual Communication-Local Area Network uses all three

Data Casting

Sleep Mode & Wakeup Function

Not all systems have sleep mode When a system with sleep mode judges that the vehicle is not being used, it stops communication of all ECUs to reduce parasitic current (BEAN, CAN, LIN)

• All doors are closed

• After a predetermined time the system goes to sleep.

Wake-up

During sleep, if any of the relevant switches are operated:

• Open the door

• Unlock the door, etc.

the affected ECU sends a “wake-up”

message to other ECUs.

Wake-up signal

In the BEAN and LIN protocols, ECUs periodically transmit data This activity

uses battery voltage and creates a normal parasitic draw To reduce

parasitic drawwhen the vehicle is not being used, ECUs enter “sleep” mode after a set time when the ignition is off and the doors are closed

After the ignition has been turned OFF, a CAN node may also enter sleep mode to reduce the power consumption The transmitter portion of the transceiver module is switched OFF, however the receiver part can remain active to check for activity on the bus

When any network-related switch is operated, the associated ECU “wakes up” and sends a wake up signal to all the other ECUs on the network

In a LIN network, both the master and slaves are able to wake-up the network

AVC-LAN does not have a sleep mode and wake-up function

• A dead battery from a parasitic draw can be caused by a BEAN, LIN, or

CAN network that is not going to sleep

• A network can be kept awake if one of the ECUs on the network is receiving

constant input from a faulty switch or sensor.

• Circuits operating properly can also keep a network awake - an immobilizer key left in the key cylinder (with ignition off) for example

Sleep Mode

Wakeup Function

SERVICE TIP

Body Electronics Area Network (BEAN)

Topology:

• Daisy chain configuration to improve reliability in the event of open circuit

• Single-wire voltage drive (speed = 10 kbps)

2004 Avalon MPX2

Body ECU

Theft Deterrent ECU

MPX2 MPX1

Power Seat ECU

MPX1

Driver Door ECU

Passenger Door ECU

The Body Electronics Area Network (BEAN) is a proprietary network developed by Toyota It is a low-speed protocol typically used for ordinary body electrical systems such as windows, doors, mirrors, seats, etc

The BEAN uses a combination of the ring and bus styles to network its ECUs This style of connection is also called a daisy chain The advantage of a ring configuration is that the ECUs in the ring part of the network can continue to communicate even if there is an open in one area because the transmission can travel via two possible pathways

Even in the ring configuration, if the communication line is cut at more than one point, communication becomes impossible In recent Toyota systems, however, a back-up bus is provided to maintain limited communications A backup bus usually links the combination switch, front Controller, and Main Body ECU

Several BEAN networks may be connected to each other via a Gateway ECU

or to other networks via the GatewayBEAN also provides the capability for customizing certain system settings using Techstream

Body Electronics

Area Network

Local Interconnect Network (LIN)

Master-Slave Protocol:

• Master sends request for data to the slave

• The slave responds with data requested

• Slaves cannot transmit unless requested (except for “wake-up” message)

• Slaves cannot communicate with each other

LIN

Master ECU Slave

ECU

Slave ECU

Slave ECU

Slave ECU

Speed = 20 kbps (e.g Power Window Master Switch, Sliding Roof ECU, etc.)

LIN was developed by a consortium of European car manufacturers as a lower cost alternative to CAN Though its maximum transmission speed is only 20 kbps, its cost is two to three times lower per node It is typically used

to control sensors and actuators in non-critical systems such as windows, doors, seats and air conditioning systems

The LIN protocol uses an AV (automotive vinyl) single wire in a star topology

to create a master-slave configuration Because each of the slaves are connected directly to the master, nodes may be added to the network without requiring hardware or software changes

In the master-slave configuration, slaves can only communicate with the master, and can send data only after receiving a data request from the master

Because each slave is separately connected to the master, a failure in any part of the network does not affect the rest of the network

BEAN was developed by Toyota as a proprietary network before wide automotive networks were available Because LIN has now appeared as

industry-an industry stindustry-andard industry-and is also a low-speed, low cost network similar to BEAN, it is replacing BEAN in most newer Toyota vehicles

LIN Characteristics

Local Interconnect

Network

LIN Replacing

BEAN

LIN has a multiple slave network architecture with a message identification for multi-cast transmission between any network node It shares some of the features of an AVC-LAN network except that a LIN master ECU contains a gateway function which has the capability to interface with higher-level networks such as CAN This feature extends the benefits of networking all the way down to the individual sensors and actuators.

Local Interconnect Network (LIN)

Topology:

• Master ECU is connected to the CAN network

• Master serves as a gateway for up to 64 slaves

• Single-wire voltage drive

ECU

Slave ECU

Slave ECU

Slave ECU

Slave ECU

LIN Gateway

Function

Controller Area Network (CAN)

EPS ECU Engine ECU (ECM)

Air Conditioner Amplifier

SIL

DLC3

CAN-H CAN-L

: CAN Main Bus Line (High) : CAN Sub-Bus Line (High) : CAN Main Bus Line (Low) : CAN Sub-Bus Line (Low) : Serial Communication Line

Topology

• Bus style with terminating resistors at each end

• Sub-bus lines connect ECUs and sensors to the main bus line

• Twisted-pair differential voltage drive

Terminating Resistors (120 ohm)

CAN HS = 500 kbps (max 1 Mbps)CAN MS = 250 kbps

Certification ECU Meter ECU

Skid Control ECU

Main Body ECU

Airbag Sensor Assembly

Steering Angle Sensor

Yaw Rate Sensor

Deceleration Sensor

The Controller Area Network (CAN) was originally developed specifically for automotive applications by Bosch and later adopted as a standard by the International Standards Organization (ISO) It has since been adapted for use

in elevators and medical device applications

Similar to BEAN, multiple ECUs are connected to a common CAN bus However, CAN is not designed for use in a ring topology, and is limited to a maximum of 13 ECUs on a single network To accommodate more ECUs, multiple CAN networks can be linked by Gateway ECUs

CAN uses twisted-pair wiring to carry matching high and low voltage signals for reliability and speed It comes in two varieties– HS (high-speed, 500 kbps) and MS (medium-speed, 250 kbps)

The CAN bus uses 120 ohm resistors at each end of the bus to prevent signals from bouncing back and corrupting communications Since each bus has two resistors between CAN high and CAN low, the resistance between the two CAN bus lines is approximately 60 ohms

Controller Area

Network

Terminating Resistors

AVC-LAN is a unified standard developed by six companies including Toyota Motor Corporation The intention was to standardize signals such as audio signals, visual signals, switch indication signals and communication signals The purpose for the standardization was to avoid the incompatibility that resulted when products from more than one manufacturer were combined in a single multimedia system.

When the AVC-LAN is linked to other networks, a Gateway ECU (or a gateway function integrated in another ECU) is needed

Audio Visual

Communication

-Local Area Network

Audio Visual Communication – Local Area Network (AVC-LAN)Topology:

• Master-slave configuration using differential voltage drive

• Broadcast, unicast, and multicast communication

Speed = 17.8 kbps

Audio Head Unit

Stereo Component Amp.

Stereo Component Tuner

Television Camera ECU

Driver Side J/B ECU

Multi Display (Master)

Audio Head Unit

Stereo Component Amp.

Stereo Component Tuner

Television Camera ECU

Driver Side J/B ECU

Multi Display (Master)

Audio Visual Communication – Local Area Network (AVC-LAN)Control:

• Each component has an ID The one with the lowest ID is the master

ID: 1F4

Note: IDs are hexadecimal numbers

An AVC-LAN system consists of audio units and ECUs that are connected in parallel Each of these units has a switch to connect the unit to the

communication bus

When the ignition switch is turned to the ACC position, the vehicle’ s LAN System Master Unit sends a registration request on the system’s LAN circuit At that time, the mode control portion of the system transmits a

AVC-physical addressback to the Master Unit The physical address is a digit code designation for each of the components of the system (such as the Navigation ECU, Television Camera ECU, Stereo Component Amplifier, etc.)The mode control portion of the system provides communication traffic control and transmits output ON, and output OFF instructions to each of these units when switching from one operation unit within the system to another

three-All of the components in the system transmit a logical address from each unit

The logical address is a two-digit code (in hexadecimal) that is assigned to

each function for that unit (such as command switch, speaker beep, etc).The mode control portion of the system then verifies the connection and operation of each of the components

The numeric IDs are given in hexadecimal numbers Hexadecimal is the

base-16 number system used by computers where A = 10, B=11, C=12, D=13, E=14, and F=15

In vehicles with a multi display (ID = 110 or 118) , the multi display is the master In vehicles without a multi display, the radio receiver (ID = 190) is the master

AVC-LAN Protocol

NOTE

Certification ECU Driver Seat ECU Multiplex Tilt and Telescopic ECU Outer Mirror Control Tire Pressure Warning ECU Bus Buffer ECU

Gateway ECUs

Some ECUs have an integrated gateway function

If different types of networks connect to one ECU, you can assume it has a gateway function

2009 Land Cruiser

Rear Heater Control Panel

Immobilizer Code ECU

Steering Lock ECU

Main Body ECU (with gateway

Navigation ECU*

Television Display* Radio Receiver Assembly

Stereo Component Amplifier Assembly Skid Control ECU Yaw Rate Sensor Assembly Seat Belt Control ECU Steering Sensor Skid Control ECU* Warning ECUClearance

ECM A/C Amplifier

Assembly

Center Airbag Sensor Assembly Meter AssemblyCombination Multi-Display*

Front Heater Control Panel

Sliding Roof ECU Power Window

ECU

CAN

Movement Control Bus (HS)

*: Option

DLC3

Network Gateway ECU

Network Gateway ECU

CAN

MS Bus

LIN CAN AVC-LAN

Components on networks using different protocols can’t communicate directly with one another because they don’t “speak the same language.” To translate and relay messages between networks, Gateway ECUs were developed

A Gateway ECU also serves as the interface between vehicle networks and the diagnostic tester (via the DLC3 connector)

In many systems, a major ECU (such as the Main Body ECU) may include a gateway function within it If different types of networks connect to one ECU, you can assume it also serves as a Gateway ECU

A vehicle may have multiple Controller Area Networks for a variety of reasons

• A CAN bus can have no more than 13 nodes To link more than 13 components using CAN requires two or more networks

• CAN buses may be different speeds (HS or MS)

• Multiple buses are often intentionally used so that a failure in one bus doesn’t disable components on other CAN buses

To link multiple CAN buses together, a CAN Gateway ECU can be used

Gateway ECU

CAN Gateway ECU

Gateway ECU Functions

Communication:Provides communication

link between multiple buses of the same

Diagnosis:Stores DTCs for BEAN networks

Interface:Translates messages from one

Gateway ECU

BEAN

The Gateway ECU connects buses of different protocols and DLC3, and

manages communications between them It also provides signal conversion

between the BEAN, CAN, and AVC-LAN networks

Gateways also regulate the exchange of data between networks of the

same protocol, such as two BEAN networks Separate BEAN networks ensure that a failure in one network won’t disable all BEAN components.BEAN networks are connected to the DLC3 via the gateway and the gateway communicates with the diagnostic tester The gateway does not interpret the messages; it simply transfers the Diagnostic Requests onto the BEAN and then transfers Diagnostic Responses from the BEAN onto ISO 9141 (the diagnostic protocol) If a malfunction occurs in the BEAN communication, DTCs are stored in the gateway memory

The gateway acts as a kind of firewall to prevent the entire system from

being affected if one bus fails

The gateway enables the customize feature of BEAN networks.

Summary of

Gateway ECU

Functions

CAN Gateway ECU Functions

Data destined for components on the other bus is relayed

Data not intended for components on the other bus is not forwarded

DTCs are stored in the

CAN Gateway ECU

ECU

CAN Gateway ECU ECU

ECU

ECU

ECU ECU

ECU

A CAN Gateway ECU has fewer but more specialized functions.

Compared to other Gateway ECUs, the CAN Gateway ECU’s functions are simplified:

•Forward data from one bus to the other when the data is addressed to

components on the other bus

•Restrict transmission of data to the other bus when the data is not

addressed to any components on that bus

•Store DTCs for failure in components or communication lines.

CAN Gateway ECU

Functions

Transmit/Receive ChartsAir Conditioning System Diagram

A/C Amplifier

ECM BEAN/CAN

Heater Relay Control Signal Magnetic Clutch Control Signal Rear DEF Relay Control Signal Idle Up Signal

Pressure Sensor Signal External Variable Control Solenoid Current Signal Multiplex Network

Body ECU

BEAN Diagnostic Tool Response

Diagnostic Data Accessory Meter

Assy

BEAN / LAN

AVC-Indicator ON demand signal

DLC3

ECM

BEAN AVC-LAN

CAN

ECM

Gateway ECU Accessory

Meter Assy

Combination Meter Assy

Multiplex Network Body ECU

Front Controller A/C Amplifier

The transmit/receive charts in the Repair Manual can be very helpful in understanding the operation of a multiplex circuit The example above is just

a portion of the chart for the air conditioning system of a 2005 Avalon

These charts can be found in the System Diagram section of the Repair Manual for each system using multiplex communication

Transmit/Receive

Charts

BEAN Communication Signal

BEAN uses a single wire voltage drive protocol The BEAN communication signal varies from zero to a nominal 10 volts The circuit is at rest when at zero volts

BEAN Signal

BEAN Diagnosis

Communication line disconnection or open at 2 points DTC No Detection Item Detecting Condition B1200 MPX Body ECU communication stop Communication with Gateway ECU

stopped 10 sec or more B1271 Combination meter ECU communication stop

Communication line short

B1214 Short to B+ in door system communication bus malfunction

When a +B short circuit is detected

in the door system communication bus

B1215 Short to GND in door system communication bus malfunction

When a body ground short circuit is detected in the door system communication bus Check DTC information

2008 Avalon

Examples

The Gateway ECU monitors communication on the BEAN and stores a DTC when it detects a network communication error (DTC B12XX) The Gateway ECU outputs only B12XX DTCs

Note that DTCs indicating “communication stop” typically mean there is a disconnection or open circuit that is isolating one more ECUs from the network You can determine the possible locations of the open circuit by examining the wiring diagram and analyzing which ECUs are offline

Because short circuits disable the entire network, those DTCs do not identify

a particular ECU The diagnostic procedure for shorts involves disconnecting portions of the circuit until communication resumes You then know the short

is in the disconnected portion of the circuit

BEAN Diagnosis

Defective combination meter ECU power supply or ground

BEAN Diagnosis – Open Circuit

DTC No Detection Item Detecting Condition B1271 Combination meter ECU communication stop Communication with Gateway ECU

stopped 10 sec or more

: Communication Circuit

Communication line disconnection or open at 2 points

Connector disconnected

Failure in Combination Meter ECU

Defective inner communication line in each ECU

Components connected to the BEAN in a ring style (daisy chain) have two paths for data flow around the ring, so a single open in the network does not stop communication Two opens in the communication line, however, will isolate one or more ECUs

In the example above, the Combination Meter ECU has become isolated The potential problem areas are:

• A loss of power or ground to the Meter ECU

• Failure inside the Meter ECU

• Meter ECU connector disconnected

• Two opens in the wire harness leading to the Meter ECU

• Failures in the internal communication lines of the two ECUs connected to the Meter ECU

Open Circuit

BEAN Diagnosis – Short Circuit

DTC No Detection Item Detecting Condition B1215 Short to GND in door system

communication bus malfunction

When a body ground short circuit is detected in the door system communication bus

Communication line short

When a communication line is short-circuited to B+, the entire line is 12V, and

if short-circuited to ground, it’s 0V Being unable to vary the voltage on the line, the Gateway ECU cannot communicate with any ECUs so it is impossible for it to determine the location of the short

To locate the short, disconnect each ECU one by one and check what DTC is output

Short Circuit

BEAN Diagnosis – Short Circuit (Step 1)

If communication does not resume, the short

is still in some other part of the network. : Communication Circuit

disconnected, network communication will resume

To determine when the network is communicating again, you can connect a DVOM or oscilloscope to the BEAN circuit at the Gateway ECU When voltage or a signal reappears on the circuit, the most recent component disconnected is the one with the short

Another way to check for communication is to examine DTCs after an ECU is disconnected In this example, the Meter ECU is disconnected first

If DTC 1215 (communication line short) is still present, then the Meter ECU is not the problem; the short is still in the part of the circuit connected to the Gateway ECU Continue to the next step

• If DTC 1271 (Meter ECU stop) occurs, then the short circuit is no longer present in the network and it is working again This means the short must be

in the disconnected Meter ECU Replace it

Don’t disconnect the Gateway ECU because that’s where the DTCs are stored When DLC3 is connected to the Gateway ECU, disconnecting the

Short Circuit Step 1

NOTE

BEAN Diagnosis – Short Circuit (Step 2)

If the fault is not found, disconnect the next ECU and recheck for

communication.

If communication resumes after the Body ECU is disconnected, the short is in harness B” or in the Body ECU Reconnecting the Meter ECU will tell you where the short is (Step 3).

“A”

“B”

“C”

“D”

If communication does not resume, the short is still

in some other part of the network Reconnect the Meter ECU, then disconnect the A/C ECU (Step 4).

: Communication Circuit

Continuing trouble shooting this example, disconnect the next ECU after the Meter ECU and check if the communication signal reappears

If checking DTCs:

• If DTC 1215 (communication line short) is still present, then the harness “B”and the Body ECU are not the problem The short is in the part of the network still connected to the Gateway ECU Continue to step 4

• If DTC 1271 (Meter ECU stop) and DTC 1200 (Body ECU stop) occur, then the short circuit is no longer present in the network Since you already ruled out a problem with the Meter ECU, this means the fault must be in the disconnected harness “B” or in the Body ECU To diagnose which, continue to step 3

Short Circuit Step 2

BEAN Diagnosis – Short Circuit (Step 3)

If fault is found, isolate the location by reconnecting the first ECU and

rechecking for communication.

If communication

continues, the short is

in the Body ECU that

is disconnected from

the network.

If communication stops when the Meter ECU is reconnected, that means the short is in the harness that was just reconnected to the network.

To determine if the problem is in harness “B” or the Body ECU, reconnect the Meter ECU

If communication stops, the short is in harness “B” If communication continues, the short is in the Body ECU

If checking DTCs:

• If DTC 1215 (communication line short) occurs again instead of DTC 1200 (Body ECU stop), then the short has been reconnected to the part of the circuit connected to the Gateway ECU It has to be in harness “B” Replace it

• If DTC 1200 (Body ECU stop) remains, the short circuit has been isolated from the network The only part not connected to the network is the Body ECU Replace it

Short Circuit Step 3

BEAN Diagnosis – Short Circuit (Step 4)

If the fault wasn’t found, continue isolating the problem by

disconnecting the next ECU and rechecking for communication.

If communication

resumes, the short is in

harness “C” or the A/C

ECU Reconnect the

Body ECU and recheck

for communication (Step

If communication does not resume, reconnect the Body ECU, and go to step 6

If checking DTCs:

• If DTC 1215 (communication line short) is still present, then the harness “C”and the A/C ECU are not the problem because they are no longer connected

to the Gateway ECU Continue to step 6

• If DTC 1200 (Body ECU stop) and B1262 (A/C ECU stop) occur, then the short circuit is no longer present in the network This means it must be in the disconnected harness “C” or in the A/C ECU To diagnose which, continue to step 5

Short Circuit Step 4

BEAN Diagnosis – Short Circuit (Step 5)

If fault is found, isolate the location by reconnecting the

previous ECU & rechecking DTCs.

If DTC 1262 (A/C ECU stop), then the short is in A/C ECU.

If DTC 1215, then

the short is in the

part of the network

that was just

• If only DTC 1262 (A/C ECU stop) is present, then the short circuit is no longer present in the network This means it must be in the disconnected A/C ECU Replace it

Short Circuit Step 5