GENERIC AUTOMOTIVE PROTOCOLS

GENERIC AUTOMOTIVE PROTOCOLS

To date I've evaluated several VW, AUDI, SKODA and SEAT scan tools and discovered that there are many, many readers who have no idea what generic automotive protocols are or what a automotive scan tool does. The following is an explanation of automotive protocols, but if you like, you may download the PDF document that identifies which protocol / protocols are specific to your vehicle's make and model. To make things simple, if your car was manufactured after 2008 then your vehicle soley uses the  CAN protocol, whereas if it was manufactured prior to Y2K then it's very likely that it soley uses the ISO 9141 protocol, but there are exceptions. Cars manufactured between Y2k and 2007 inclusive, uses one, two or three of the ISO diagnostic protocols.

ISO stands for 'International Organization for Standardization' and is a Worldwide Federation to which  most national standards bodies situated in most countries are affiliated to, as members. Member bodies interested in a specific subject, automotive or electrical or otherwise, for which a technical committee has been established, has the right to be represented on this committee. Any draft International Standards adopted by these technical committees are then circulated to all member bodies and publication of the impending International Standard requires approval by a 75 % member majority vote before it can be accepted as cast in stone. The numbers 9141 / 1430 / 15765 are just numerical numbers allocated to standard when approved and gives you some idea as to how many standards they already approved.  ISO 9141 has been amended and is now known as ISO 9141-2.

The various colour lines depict the various bus systems. In the drawing only three modules for each bus system is shown but there could me more than 10 modules per system hence the open ended arrows. As can be seen, the Powertrain bus, the Diagnostic bus, the Infotainment bus, the Lin Bus, the Instrument panel bus and the Convenience bus are all disparate bus systems that converge at the Gateway module which is responsible or protocol translation between the various bus systems.

Anyway,  VAG vehicles predominantly use either ISO 9141-2 ("CARB"), or ISO 1430 ("KWP-2000") [Keyword Protocol 2000]  or the  ISO-15765 ("CAN") [Controller Area Network] protocol and these are the languages of OBDII (On-board Diagnostic 2) systems.   Some VWs support all three protocols and the scan tool normally used the protocol best suited for communication subject to the mission criticality and speed of the individual networks. There are other protocols in use by different car manufacturers like, LIN (Local Interconnect Network) Bus, and FlexRay, Byteflight,  and MOST (Media Oriented Systems Transport) etc... but these are not the only bus protocols used in electronics.

For example HTTP (Hyper Text Transfer Protocol),  SSL (Secure Socket Layer), TCP/IP (Transmission Control Protocol Internet Protocol) are protocol that come to mind that are used for internet communication. Then there is the WI-FI protocol for cell phone or laptop  to router communication, then there is  Bluetooth for cell phone to cell phone communication or computer to printer communication to mention but a few.

A protocol is essentially a set of rules that determines the interchange of digital information between on-board emission-related Electronic Control Units (ECUs) or two bus enabled electronic devices. Restated, how the electronic modules in your car communicate with one another and how  they communicates with a scan tool in order to display, read and clears DTC's. DTC stands for Diagnostic Trouble Codes. You may download this PDF of generic trouble codes specific to VW, Audi SEAT and SKODA vehicles. A scan tool can exchange digital information with any of many electronic modules to establish the correct module coding based on installed equipment. A basic set of modules are

Address 01: Engine   - Engine Control Module (ECU)

Address 02: Auto Trans  Transmission Control Module (TCU)

Address 03: ABS Brakes  - Assisted Braking System Module (ABS)

Address 08: Auto HVAC  - Heating, Ventilation and Air Conditioning

Address 09: Cent. Elect.  - Central Electronics Control Module

Address 15: Airbags  -  Supplemental Restraint System (SRS)

Address 17: Instruments  - Dashboard cluster

Address 19: CAN Gateway - On-Board Power supply

Address 25: Immobilizer - Immobilizer Control Module

Address 44: Steering Assist - Power steering Module

Address 45: Inter. Monitor - Interior Control Module

Address 46: Central Conv.  - Central Convenience Control Module

Address 56: Radio - Radio Control Module

Getting back to the rules, a protocol is commonly called a hand shake. It takes to parties to commit to communication. Its something like when someone comes to knock at your door, and when you hear the knock , you go answer the door. The person at the door greets and you return the greeting because it is protocol to do so. The visitor asks if this is number '303 steering module street' and you say yes. He then say he represents the electricity department and needs to take a reading of your electricity meter, you agree for him to enter. He then capture the information in his palm top, thanks you for you cooperation and you let him out and closed the door behind him. 

Likewise the scan tool (someone at the door) sends a signal (knock on the door) to the engine control module or the steering control module, or the gateway modules. The relevant module (you) receives the signal and decodes it, then determines (the nature of business) that the scan tool requests access to its internal non-volatile memory. Because the request signal had the appropriate greeting, the relevant control module reciprocates and allows its contents to be read. Thereafter the scan tool transmits an  exit signal and the control module releases or shuts down communication.  That basically describes a successful yet very simplified digital information interchange between scan tool and control module. However, all this is done in  naughts and ones, the bits and bytes of binary code and is a lot more intricate than described but the objective was just to give you a general idea of function of a  protocol. 

CAN-bus is used for the Drivetrain Network
CAN-bus is used for the Instrument Cluster/Suspension Network 
CAN-bus is also used for the Convenience Network
CAN-bus or LIN or MOST is used for the Infotainment Network
CAN-bus is also used for the Diagnostic Network