Controller Area Network - Design & Function (Coupe): Other Volvo C70 I

General

CAN (Controller Area Network) is a standardized system for multiplex communication. Multiplex communication means that you can transmit messages between one or more control modules on the same wires without communication between the various control modules disrupting one another. Volvo has produced a new standard for multiplex communication, known as VOLCANO. VOLCANO is a further development of CAN and works with real-time processing, as well as prioritization. The description of prioritization is based on VOLCANO but named CAN.

The standard for Control area network (CAN) specifies

1. That two cables should be used (CAN H and CAN L)
2. Which voltage levels should be used
3. What a message should look like
4. How transfer errors should be handled.

Scheme 452

The wires CAN H and CAN L must not be confused with HS CAN and LS CAN, which indicate the speed of the CAN network. CAN H and CAN L are the names for the wires used to distribute the signals in the multiplex communications network.

Communication takes place using two wires. These two wires are twisted together and are made of a copper material.

The voltage levels for communication take place using differential voltage levels. Two twisted-pair wires and differential voltage levels are used because this makes the network less susceptible to interference.

The same message is transferred simultaneously by both cables, but different voltage levels are used.

1. Binary 1 = 2.5 V on both CAN H and CAN L.
2. Binary 0 = 4 V on CAN H and 1 V on CAN L.

When measured between CAN L and earth, the average voltage level is approx. 2.3 V.

When measuring between CAN H and ground, the average voltage level is approx. 2.8 V. When measuring between the two CAN wires, with normal traffic on the network, the average voltage level is approx. 0.55-0.90 V (up to max. 0.6-1.4 V).

Volvo's CAN-net meets ISO 11898-2. Other standard is 11898-3 where the voltage on CAN H changes from approx. 5 V to approx. 1 V, and CAN L from approx. 0 V to approx. 4 V when changing from logic "0" to logic "1". Other standard is SAE J2411 where only one cable is used for CAN-communication.

Scheme 453

The message consists of the following components

1. Identifier ("flag"), which indicates the message's identity and priority.
2. Data information (value, information, etc.).
3. Check sum, used to check that the message has arrived correctly
4. Stop signal, which indicates that the message has finished.

A complete CAN-message is called a frame.

Prioritizing

Conflicts can occur in a network when several control modules wish to send a message at the same time. For example when the driver presses the brake pedal at the same time as the passenger changes the climate control settings and a passenger in the rear seat opens the power window.

For safe function the messages have to be prioritized. In addition the time delays which occur in case of queue situations must be held within reasonable limits. This is so that the customer does not experience the system as "sluggish" or slow.

To solve problems with conflicts and time delays there is a priority order of messages to ensure good functionality.

Prioritization of messages is determined by the number of zeroes at the beginning of a message, the more zeroes the higher the priority.

Prioritization occurs as follows

1. When the network is available, all the control modules that have "something to say" send bit one in their message.
2. All the control modules detect what has been transmitted on the network
3. If a control module has transmitted 0 those that have sent 1 stop and wait until the next time the network is available
4. Those that transmitted 0 transmit bit two of the message
5. If a control module has transmitted 0 as bit two those that have sent 1 stop and wait until the next time the network is available and so on.

The message with the highest priority (most zeroes at the beginning) "wins" and is sent first.

The end of a message is seven zeroes. The control modules then know that the network is available and a new message can be sent in priority order.

Two Types Of Message

There are two types of message in the system

1. Periodical frames . These messages are sent regularly and give the status of a parameter. They are used for information which is frequently updated, speed signals for example.
2. Event frames , which are only sent when predetermined conditions have been met. This type of message is used for things that seldom occur, raising/lowering a window for example.

The message can contain an update bit which states how "fresh" the information is.

The system assumes that the receiver has received the message so an acknowledgment is not sent (a reply is only sent to a direct question from another control module).

However, the receiver "knows" how often it should receive a message about which status applies. If the message is missing, the receiver can connect an emergency program and/or generate a diagnostic trouble code.

Diagnostic trouble codes (DTCs) can also be stored if the receiving control module does not "understand" the message it has received. Examples of this may include intermittent short-circuits between one of the CAN wires and voltage or earth.

Quality Factor

In a distributed system where information (signals) is sent between different control modules in a network, it is usually the control module that generates/creates information (the signal) that knows the quality of the information that is sent. To be able to inform receiving control modules about the quality of information, a quality factor (Q-factor) is sent over the network at the same time as the information (signal). The quality factor describes status of the information (signal). For example, if the signal is defective due to a faulty sensor, a receiving control module can use the quality factor to decide if the control module shall take any action (e. g., reconfiguration).

The quality factor can be of the following status

1. OK The value indicates that the signal is normal and shows a credible status and accuracy.
2. Outside specified range Even though the value indicates that the signal is normal and may be usable, some fault has been detected that indicates that accuracy has been reduced so that performance may be affected or instability can occur.
3. No data found The value indicates that the signal has its initial start-up value and has not yet had time to receive measured or calculated value. This may occur when the control module's start-up process is not completely finished. As soon as the control module has started, the signal shall have a correct value. Receiving control module has a built-in delay to wait for correct signal.
4. No data exists The value indicates that the signal is faulty. This prevents the signal from being used by receiving control modules.

Summary Of Quality Factor That May Apply.

*Diagnostic trouble code may be stored.

Compatibility

The units must "speak" the same language and must be compatible with each other. A standardized communication protocol is used for this.

Signal configuration (sfg) contains the language between the modules. If any module has a signal configuration which does not tally with other modules, this module is unable to communicate with other modules. This means that all modules must have compatible signal configuration. The signal configuration is sometimes changed as new messages are added and old ones are deleted.

Configuration

Instructions for the following are downloaded when a system is configured

1. Which control modules are included in the system (for example central electronic module (CEM), and others.)
2. Which control module should do what (for example "you are the control module for the driver's door - you are the control module for the passenger door")
3. Which functions should be included (for example if the alarm function should be on or off)
4. Which components are connected to the control modules (for example whether the inclination sensor is included in the alarm or not)
5. Which messages a control module is to transmit and which it is to receive
6. Where the different data should be stored.

In the central electronic module (CEM), information is stored on which control modules are installed in this particular vehicle. This information is stored and retrieved from Volvo's central database when software is downloaded. The central electronic module (CEM) also contains information on which primary signal configuration is to be used in the vehicle. Information on the vehicle's signal configuration must be stored in all control modules connected to the CAN network so that they can communicate in the first place.

The signal configuration is a part of the software downloaded after a control module is fitted or replaced. When software is loaded to a control module, the information in the control module indicating, for example, that a new accessory has been connected is updated automatically.

Once software has been downloaded, some values may be changed according to the customer's requirements, for example whether lamp indication upon locking or unlocking the vehicle should be active, or the dip degree of the interior rear view mirror. These settings may disappear when new software is downloaded.

Software is downloaded via the Software Manager.

Note. Even if two vehicles appear identical they may behave differently due to differing configurations, a parameter may have been modified by, e. g., the customer or workshop.

The network is made up of a number of control modules (sometimes called nodes) which are connected to each other serially via two communication cables. Each control module is supplied with power and grounded individually and receives messages/commands via the two communication cables. In both networks (high and low speed sides) the control modules are serially connected. In the event of an open-circuit those control modules beyond the open-circuit will not be able to communicate with other parts of the network.

Scheme 454

The network consists of two parts: a high speed side (HS CAN) which transmits signals/messages between the central electronic module (CEM) and control modules mainly in the engine compartment, and a low speed side (LS CAN) which transmits signals/messages between the central electronic module (CEM) and control modules in the passenger compartment and the luggage compartment.

The interface between the high and low speed sides is supplied by the central electronic module (CEM) which converts the transmission speed up or down for communication between the two network sides.

Scheme 455

The data link connector is located in the passenger compartment near the driver's station, cables for high-speed side (HS CAN) and low-speed side (LS CAN) are connected to the data link connector.

Scheme 456

1. Pin 3 LS CAN (low-speed side) (H-cable)
2. Pin 4 Chassis ground
3. Pin 5 Signal ground
4. Pin 6 HS CAN (high-speed side) (H-cable)
5. Pin 11 LS CAN (low-speed side) (L-cable)
6. Pin 14 HS CAN (high-speed side) (L-cable)
7. Pin 16 Voltage feed

Note. The data link connector's other connections may be used by other functions. This service information only describes connections related to CAN.

Transfer Speeds

The Volvo Controller area network (CAN) has two transfer speeds.

1. HS CAN (high speed) has a transfer rate of 500 kbit/s.
2. LS CAN (low speed) has a transfer rate of 125 kbit/s.

1 kbit/s = 1024 bits per second (1 byte = 8 bits).

For serial communication (Volcano Lite) between a control module and a slave control module the transfer rate is 10.4 kbit/s.

There is another serial standard known as LIN. This is an international standard which is becoming more commonly used. Its function is almost identical to that of Volcano Lite. The difference is in the communication method and rate. The transfer rate for LIN is 9.6 kbit/s.

Terminating Resistor

High-speed net HS CAN (High Speed), example

Scheme 457

Low-speed net LS CAN (Low Speed), example

Scheme 458

To prevent electrical reflections and interference in the CAN network, there are terminating resistors which bridge CAN H (High) and CAN L (Low), one at each end (main line) on both the high and low speed sides of the network. Each terminating resistor has a resistance of 120 ohm

1. For HS CAN (high speed), the terminating resistors are located in the brake control module (BCM) and the engine control module (ECM).
2. For LS CAN (low speed), the terminating resistors are located in the upper electronic module (UEM) and the rear electronic module (REM).

Resistance measurement of parallel circuit with terminating resistor

Both the terminating resistors create a parallel circuit The following resistors can be measured under specified conditions

1. When the CAN network is intact, the resistance on the network is approx. 60 ohm.
2. In case of open circuits on the cables, so that 1 terminating resistor is not included in the circuit, the resistance in the net is approx. 120 ohm (only one main line is measured)
3. An open circuit on the cables to control modules located "outside" the measured circuit cannot be detected with this measurement.
4. In case of short-circuiting between the communication cables, the resistance is approx. 0 ohm between the cables, regardless of where the short-circuiting is located.

Scheme 459

Scheme 460

Scheme 461

The number of control modules in the CAN network varies depending on the car model, equipment level and structure week, The structure week and construction week are not necessarily the same week. The construction week is the week in which the vehicle is built in the factory. The content of the vehicle is steered towards structure week. A structure week may extend over a number of construction weeks. Structure weeks are specified in the format YYYYWW.

For example, structure week 199815 indicates that the structure week of the vehicle is week 15, year 1998.

Note. To troubleshoot respective CAN-net, see troubleshooting for CAN-related diagnostic trouble codes for Central electronic module (CEM). For example, choose any of CEM-DF01-DF17 depending on CAN-net.

The CAN network is monitored by the central electronic module (CEM). When the central electronic module (CEM) detects a fault in the CAN network, a diagnostic trouble code (DTC) is stored in the central electronic module (CEM). There are various types of diagnostic trouble code (DTC), depending on the type of fault.

Types of error which are handled are

1. Electrical faults
2. No communication from the control module
3. Faulty communication.

Electrical Faults

When there is a fault in the signal levels on the communication wire to the central electronic module (CEM), a diagnostic trouble code (DTC) is stored in the central electronic module (CEM). Each individual communication wire to the central electronic module (CEM), CAN L and CAN H on the low speed side of the network and CAN L and CAN H on the high speed side of the network, is checked. There are two different levels detected on each wire: short-circuit to voltage or short-circuit to earth. As the central electronic module (CEM) can also determine when a short-circuit on one or more wires takes place, the control module can also detect a short-circuit between the two CAN wires in the same part of the network.

This gives eight diagnostic trouble codes for detecting electrical faults.

HINT: The central electronic module (CEM) is unable to store diagnostic trouble codes (DTCs) for open-circuits on the CAN wires. Other diagnostic trouble codes (DTCs) may, however, be stored on account of this.

No Communication From the Control Module

The central electronic module (CEM) knows which control modules should be present in the CAN network and checks at regular intervals to ensure that all control modules are communicating. If any control module in the CAN network is not communicating, a diagnostic trouble code (DTC) is stored in the central electronic module (CEM). There is a specific diagnostic trouble code (DTC) for every control module in the CAN network.

Faulty Communication

Every control module, apart from the central electronic module (CEM), has two diagnostic trouble code (DTC) types which relate to faulty communication (the central electronic module (CEM) has only one diagnostic trouble code (DTC) type).

These are

1. Faulty messages
2. Configuration error (not present on the central electronic module (CEM)).

Diagnostic trouble code (DTC) for faulty configuration is missing from the Central electronic module (CEM) since the control module is always the main control module in the network.

Faulty Messages

When a control module transmits faulty signals in its messages a number of times, the control module shuts down communication. This is referred to as the control module going to "Bus-off". A diagnostic trouble code (DTC) is stored in the control module that transmitted faulty messages, and the control module stops communicating on the CAN network. This is done so that the control module does not interfere with other communication on the CAN network. If the fault is permanent, it is not possible to communicate with the control module and there is no chance of reading diagnostic trouble codes (DTCs) from the control module that has shut down communication as long as the control module continues to be powered. If the control module which stored a diagnostic trouble code (DTC) is powered down (for example by switching off the ignition or if the fuse to the power feed is removed), the control module will attempt again to communicate when the control module is powered up again. When troubleshooting such faults, therefore, it is important to know what kind of power feed is used for the control module in question.

Configuration Fault

The central electronic module (CEM) transmits at regular intervals a control message to all control modules on the CAN network, This message includes, among other things, the ID number of the signal configuration currently being used. The reason for this is that all control modules on the CAN network must have the same signal configuration if they are to be able to communicate.

If the ID number of a control module's signal configuration does not tally with the ID number transmitted by the central electronic module (CEM), a diagnostic trouble code (DTC) is stored in the control module with the faulty signal configuration.

The control module which stores the diagnostic trouble code (DTC) will stop communicating on the CAN network but will still monitor traffic and respond to diagnostics communication.

Faulty Signal

Faulty signal

See Frozen Values And Counter For Diagnostic Trouble Codes.

1. DONE See «Checking the Throttle Unit»(ref-439006-S14622942162011120700000)

Checking the Throttle Unit

Use the diagnostic trouble codes' frozen values as well as the counters, to determine the driving conditions when the problem was detected the first time and how often the problem has occurred. The values show the problem's current status and how intermittent the problem is. Check if the diagnostic trouble code has been generated during engine start and if the battery voltage was very low at that time.

If the trouble code was stored when battery voltage was low and engine speed was close to 0 RPM when the fault occurred, it could indicate that the fault arose when the vehicle was stationary with the ignition on for a long period, thereby draining the battery, or that the fault arose due to battery voltage becoming low when the customer started the engine. This, in turn, indicates that the battery's charging status is not OK.

Check the battery charge status, connections to the battery and chassis and the battery cables for contact resistance and oxidation.

Remedy as necessary. Otherwise, continue as follows.

If the frozen values indicate that battery voltage was OK, try a new throttle unit (ETM).

Remedy as necessary.

Other information

1. See «Throttle Body (Electronic Throttle Module (ETM)), Replacing»(ref-408503-S15001656662011071200000)
2. See «Identifying Upgraded Software ECM/ETM»(ref-438955-S16861622552011120700000)
3. See «Checking Wiring And Terminals»(ref-438953-S20310262912011120700000)

If this is not done correctly, diagnostic trouble codes may remain even after deleting diagnostic trouble codes and any reconfiguration may remain, despite the problem being fixed.

Scheme 462

1. Continue See «Fault-Tracing Information»(ref-439006-S08532434602011120700000)

Fault-Tracing Information

1. FAULT NOT FOUND Refer to «Faulty signal»(ref-439006-S02771409732011120700000) .
2. FAULT FOUND OKAY: Troubleshooting has been completed.

Checking Components, Intake System

Check using information about combined diagnostic trouble codes if this trouble code is a root problem or not. If the diagnostic trouble code is stored as lone diagnostic trouble code or if it is indicated as a root problem, continue with the troubleshooting below, otherwise follow troubleshooting for the diagnostic trouble code pointed out as root problem.

ECM-130A can be generated due to a damaged mass air flow sensor. An indication of this is that the engine control system has increased the fuel amount at partial load and then primarily the value for "Lambda adaption, upper partial load". If any of the diagnostic trouble codes ECM-260A, ECM-261A, ECM-270A and/or ECM-271A with trouble type Upper limit is stored together with ECM-130A, troubleshoot according to any of these diagnostic trouble codes, otherwise continue according to the following.

Read off "Air mass, correction value" and check in which way the air adaption has gone. A low value, less than approx. 0.85 indicates a clogged crankcase ventilation and/or dirty throttle module. A higher value, greater than approximately 1. 15, indicates a (smaller) air leak somewhere in the intake system.

High value

Check the induction system for air leaks.

Check that the intake air temperature (IAT) sensor and boost pressure sensor are correctly installed. Check for air leakage around the components.

Note. Even extremely small air leaks can cause this diagnostic trouble code (DTC) to be stored.

Low value

For markets where upgraded software, released during year 2006 or later, is available, then if ECM-91A7 and/or ECM-91B7 is stored together with ECM-130A, then the throttle module shall be cleaned.

Otherwise, the solution to the diagnostic trouble code/symptom is to load the upgraded software in the vehicle.

For markets where upgraded software, released during year 2006 or later, is not available, the solution is to clean the throttle module and the crankcase ventilation.

See Identifying upgraded software ECM/ETM

Remedy as necessary.

Other information

1. See «Information about combined diagnostic trouble codes (DTCs)»(ref-438954-S03262982102011120700000)
2. See «Air leakage in the intake system, checking»(ref-438955-S00276150322011120700000)
3. See «Throttle body (TB), cleaning»(ref-408503-S04696046242011071200000)
4. See «Mass air flow (MAF) sensor, replacing»(ref-438954-S22650523202011120700000)

Scheme 463

1. Continue Refer to «Information»(ref-439006-S11396528122011120700000)

In case of this defect, troubleshooting is not followed by verification.

The information can be displayed again or the fault-tracing for this fault can be interrupted.