A look at J2534

July 1, 2018
Today’s cars are rolling computer networks and often require software updates to fix a variety of issues.

The rate at which technology is changing personal transportation accelerates every year. While this is a challenge for technicians now, imagine what interesting experiences still lay ahead of us.

It’s a known fact that throughout the automotive industry, vehicles are becoming more and more complex, with almost every device in the modern car operated via an electronic control module. These ECMs are connected via communication networks which allow for data transfer between each other. If we strip away the mechanicals, the modern vehicle is essentially a rolling computer, using both hardware and software. Just like your home PC or laptop, the vehicle’s computers struggle with software issues, and often require updates to ensure they continue to meet emission regulations as well as addressing product quality concerns.

(Image courtesy of AutoMate) Cars have become rolling computer networks with more lines of code than even the most sophisticated combat aircraft.

Some vehicle manufactures use the same engine control module or hardware across their various models – they simply change the software to suit different operating conditions or engine and driveline configurations. This process of common hardware and network architecture, has spread throughout most vehicle manufacturers and has given rise to the concept of the “Global Car.”

The idea of a global car has many advantages, as the manufacturer can “tune” the vehicle to suit its geographical location.

J2534 programming
Reprogramming a vehicles control module (that is – updating its software, also commonly referred to as “flashing” the control module) has typically been left to an OEM dealer. One reason is that each brand has their own specific diagnostic tool for analysing, coding and reprogramming. These tools are very expensive and can often be hard to navigate. There was also a distinct lack of training in this field outside of OEM dealerships, as access to OEM data and information had generally only been available to the dealer.

With the introduction of “Pass Thru” flash programming, independent repairer’s now had a way of performing the same analysing, coding and reprograming tasks as an OEM, albeit with some limitations. Pass-Thru is a method used to transfer data between a vehicle’s control module and a laptop or scan tool. A Pass Thru device or VCI (Vehicle Communication Interface) is used for this data transfer. The VCI acts as a translator or interpreter between the PC and the vehicle’s communication network, due to the different languages or programming code used.

(Image courtesy of AutoMate) Software updates are “flashed” to a vehicle’s control module to correct shortfalls or improve product quality.

You may have heard of a VCI referred to as a J2534 device. J2534 is in fact, an interface standard designed by the Society of Automotive Engineers. The standard requests that all manufacturers use conventional methods of data communication, and allow independent repairers the ability to re-flash emission-related vehicle control units. All OBD-II compliant vehicles, must use one of the SAE specified protocols.

This simply means that only one interface tool is needed for programming multiple vehicle make and models.

There are two parts to this standard; J2534-1 and J2534-2. J2534-1 was originally developed to allow independent vehicle repairers the ability to reprogram, update and configure emission related control modules only, without the need for an OEM specific tool. J2534-2 may be used for diagnostics, reprograming and updating on all OEM supported control modules and not just emission related.

Communication protocols
One of the many hurdles that independent repairers face is the growing number and complexity of vehicle communication networks. Even basic models with very few product options can have several control modules connected to one of its networks, with high series vehicles constructed with up to five separate communication networks and fifty separate control modules. Standard J2534 dictates that any Pass Thru device must be able to communicate with all protocols used by these networks.

(Image courtesy of AutoMate) Unlike your Windows or Apple PC, the vehicle computers may interact on various networks, all speaking different computer “languages.”

Keyword, KWP2000 or K line, use the UART (universal asynchronous receive and transmit) language. UART has a very slow data transfer rate.  This is around 10.4 kilo bytes per second, with data transfer through terminals 7 and 15 in the vehicles DLC. UART is now an older language now and not readily used in current vehicles due to its low speed.

Another language or protocol, is J1850. There are two versions of this protocol. Both use PWM (pulse width modulation) for data transfer, but J1850 VPW is able to vary its transfer speed. It’s four times faster than UART and much more common. J1850 uses pins 2 and 10 to communicate with the VCI.

LIN (Local Interconnect Network) is a broadcast serial network, comprising of one master and typically up to 15 slaves. All messages are initiated by the master — with at least one slave replying to a given message. LIN devices are generally not connected to the DLC, but can be accessed via a network gateway. In most cases this will be the vehicle’s body control module.

LAN (Local Area Network) is a single wire network, used for systems that do not require a high data transfer rate. This network is perfect for comfort and convenience systems. The LAN network is accessed by terminal 1 in the vehicle’s DLC. Data transfer speeds are in the vicinity of 33 kb/sec using voltages from zero to five.

(Image courtesy of AutoMate) Different networks also send and receive data at different speeds, further complicating updates.

CAN (Controller Area Network) is available in medium or high speed, with data transfer rates of 250 kb/ sec and 500 kb/s respectively. The power train network is connected to pins 6 and 14 of the DLC. Different manufacturers may use different names and voltages for CAN, but they all derive from BOSCH. CAN is perfect for real time data exchange and pass thru programming.

MOST (Media Oriented System Transport) data bus is specifically designed for the transmission of audio and video data. MOST commonly uses fibre optic technology, transmitting at speeds up to 150 megabytes per second. This network is not connected to the DLC but can be accessed via the communication gateway.

FlexRay is utilized for advanced stability control and safety systems. This area demands higher speed communication than any current or existing Controller Area Network (CAN), bus can provide. Flex ray is an alternative to adding multiple CAN bus systems to a vehicle. Due to the data transfer rate of around 10 megabits per second (FlexRay), congestion on the network is no longer a problem.

All J2534 compliant Pass Thru devices must be able to recognize the vehicles designated protocols, and interface with the vehicles communication network for data transfer.

What is API?
Performing Pass Thru programming with a J2534 device, requires the use of an Application Program Interface (API) that will need to be downloaded to either a personal computer, laptop or even a quality scan tool.

(Image courtesy of AutoMate) Firmware is the platform between the control module and the software. Think of Windows, for example.

It’s the responsibility of each OEM to maintain and update these portals and keep current applications available for download. If you need to access these portals, a fee set by the OEM will apply. These charges will vary between manufacturers.

There are two main types of vehicle reprogramming events we can perform with a Pass Thru device and the OEM application. These are known as a Software calibration and a Firmware calibration.

Firmware is the control modules interface – which sits on a platform between the software calibration files and the control module hardware. Think about how Windows operates on your PC. The PC operating system (Windows), is similar to the vehicle control module firmware.

Windows is required to access the files and programs on your PC. If Windows has a problem, you may not be able to access your programs. Vehicle control module firmware is the same. A calibration or update to the firmware will mean a complete erasure and reprogram of the control module’s memory. This may be needed to overcome an embedded problem within the module.

Pass Thru programming and system requirements
A high speed and reliable internet connection is a necessity when re-programming a control module, as the OEM application needs to be connected and communicating with its server (wherever in the world it is physically located), throughout the entire process. 

Make sure that you have the laptop or scan tool connected to the router via an Ethernet cable, and hard wired to the vehicle when downloading any calibration files.

It’s not recommended by any OEM to perform wireless downloads and reprogramming. It is far too easy for the data transfer to be interrupted or even corrupted. This is both time consuming and frustrating as the process must be restarted from the beginning. On some newer Euro vehicles, it’s not uncommon for the vehicle control units to cycle through all their functions as part of the re-programming operation. The current draw on the vehicle’s battery may climb to be as high as 70 amps.

(Image courtesy of AutoMate) A clean supply of power is essential to a successful “flash,” and something a typical shop battery charger cannot deliver.

 A 10-minute reprogramming event with this much drain would cause the battery voltage to drop to critical levels. This would be disastrous to the module receiving the update or new calibration file. A programming power supply capable of supplying a constant 70 to 100 amps must be connected to the vehicle when performing these tasks. The power supply must also provide “clean” voltage with little to no AC “ripple” present. That means that using your shop’s battery charger is not going to work – you’ll need a battery “maintainer” designed for this task.

Installing/uploading the program
Control module coding has many different names and as many different ways to be performed but is essentially the same across all OEMs. When the new software is installed to a control module, it needs to be relinked or initialised and reconfigured with the rest of the vehicle’s network.

This “hand shake” might reinstall the security parameters to the module, record the Vehicle Identification Number, perform RPO or variant configurations, or even perform relearn procedures.

Using a VCI and an OEM application interface is not a hard task to master. The challenge for independent repairers will be having access to the OEM information and data platforms needed for re-flashing operations. Don’t be afraid to charge the customer for this service or your knowledge.

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