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
- That two cables should be used (CAN H and CAN L)
- Which voltage levels should be used
- What a message should look like
- How transfer errors should be handled.
Scheme 270
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.
- Binary 1 = 2.5 V on both CAN H and CAN L.
- 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 271
The message consists of the following components
- Identifier ("flag"), which indicates the message's identity and priority.
- Data information (value, information, etc.).
- Check sum, used to check that the message has arrived correctly
- Stop signal, which indicates that the message has finished.
A complete CAN-message is called a frame.
DESCRIPTION OF BEHAVIORS, ECM-9A0B
This information aims to give a brief description of the types of negative behavior that may be observed in the car when diagnostic trouble code (DTC) ECM-9A0B is stored in the engine control module (ECM). Scope, frequency and magnitude of a behavior depend on a large number of parameters and circumstances, which can result in variations from case to case.
HINT: Combinations of behaviors can occur.
Behavior 1
- Poor accelerator pedal (AP) response. Limited maximum speed of the car. HINT: However, a fully depressed accelerator pedal (AP) produces "normal" response without reduced maximum speed. HINT: This behavior only occurs after the car has been driven for more than 140 hours after the warning message first appeared in the display.
Behavior 2
- Limited maximum speed of the car.