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What is a Diagnostic Communication

Diagnostic Communication :

 Diagnostic Communication is base of Automotive Diagnostics.
It is an exchange of Diagnostic messages between an two entities. Those could be two ,ECUs or ECU and Tester Application.or it could be a group of ECUs and a tester application  

 The basic components of the diagnostic communication are :

 A Diagnostic Message : 
It could be of these types - 
1. A Request
2. A Response 
3. A Negative Response Code

 Diagnostic Address : 
1. Functional
2. Physical 

Diagnostic Protocol :
1. UDS
2. J1939
3. KWP 2000 etc.

Supporting Protocols : 
1. CAN
2. Ethernet
3. K-line ,etc

 What is
 Diagnostic Protocols ans supporting Protocols  ? 

 ECUs and tester communication are connected to each other by physical or wireless media. They exchange messages (requests and responses) over that physical or wireless channel. It is same as we connect to each other over internet or phone. 

 For any type of communication we need to follow a set of rules. These set of rules are called as Protocols in technical term Use of Protocol makes the communication reliable and universally understandable.  

 Reliable means whatever we send,  it shall be delivered to correct recipient within expected time and with correct content. 

 Understandable means recipient understands the message sent by sender and vice versa.

 So, for Diagnostic communication to be reliable and understandable we too follow a different Protocols and a OSI model.

 There different combinations of protocols that we can use them together for diagnostic communication. 

 Some of them are mentioned below :

 1. ISO 14229  : Unified Diagnostic Services (UDS over CAN/KWP/IP/Ethernet)
2. GMLAN 3110 : GENERAL MOTORS LOCAL AREA NETWORK ENHANCED DIAGNOSTIC TEST MODE SPECIFICATION 
3. SAE J1939  : Truck and Bus Serial Communications Vehicle Network 
4. ODB2         : Onboard Diagnostics (OBD2 over CAN /KLINE - ISO 9141/SAE J1850/ISO 14230-KWP 2000/SAE J2480 Diagnostic over CAN)
5. SAE J1979  : vehicle’s OBD systems and test equipment implemented across vehicles

 Though we have a many ways to do that, in practical scenario, use of protocols depends upon the as per the usage of ECU or market of the vehicle, OEM and ECU supplier requirements etc.

 Different ECU in a vehicle may support different protocols for Diagnostic Communication based upon their functionality and usage. Like powertrain ECUs need to support OBD2. Some ECUS may have ethernet link and then can support UDS on Ethernet. All other ECUs having only CAN may support UDS on CAN only. 

 Also different type of vehicle support different protocols.
Heavy duty vehicles(buses , trucks, JCBs, etc) use J1939. They do not support UDS on CAN for diagnostic communication.

 It is a huge list of concepts that we need to understand these protocols in depth. As most of these protocols are based on the OSI model we shall know OSI layers and its functionality of each layer. 

 for example , Physical layer : 
The basic parameter of physical layer is voltage levels(bus voltage), topology, baudrate, datarate, etc. 

 Like,If ECU is connected to CAN bus then the characteristics of CAN bus comes into picture. We will see the values of these parameters for the CAN communication.

 If we are using Ethernet then Ethernet channel then its respective characteristics and set of values will come into picture. 

 All these parameters and its suitable values are documented under respective Physical layer of the Protocols.            

 We will see it detail functionality of each layer with the example of "UDS on CAN" in upcoming posts

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