Familiarise yourself with the latest vehicle networking technologies – By James Dillon – Technical Topics.
CAN Bus was, or maybe still is, considered to be king of the vehicle networks. We have CAN Bus enabled scan tools, CAN breakout boxes, and even CAN enabled LED lighting kits. However, there are several ‘new kids’ on the block – we’ll use the term ‘new’ with a large pinch of salt, but undoubtedly, in-vehicle networking has changed and is continuing to do so. Due to the restrictions of bandwidth (capacity for data) and technological requirements, CAN is losing favour as the chosen one and the vehicle manufacturers are ushering in a new era of vehicle networking technology.
As the electronic systems within a car continue to grow in complexity, we’re seeing more sensors, controls and interfaces being utilised. All of these are leading to much higher bandwidth requirements. The different computers and domains within the vehicle increasingly need to communicate with one another in order to share their data. The complexity, cost, and weight of wiring harnesses to support this, has increased such that the wiring harness is now the third costliest and heaviest component in a car. Currently, there are several different proprietary standards for communication, with each sub-system typically using a dedicated wire/cable/network.
By moving towards a single standard, all the communications from all the different components can coexist on the same network, with a single pair or wires connecting each location in the car from a central hub or network switch. The increase in volume of data, system participants and speed requirements, mean that CAN isn’t technically able to cope with any longer.
Flexray is one of the newer standards used for inter-module communication. We’ll get into the technical nitty gritty a bit later in this article, but the headline is that Flexray runs at 20 times the speed of a typical CAN network. This speed improvement is due to distinct structural differences in the Flexray network layout, as well as enhancements to signalling and software control techniques. The improved signal speed that provides the extra bandwidth is so quick, that many automotive scopes will have a problem measuring it. The bit time in this system is measured in nano-seconds (billionths of a second), compares to CAN’s micro-second bit time (millionths of a second). In practical terms, many automotive oscilloscopes are simply incapable, because of a lack of scoping horsepower, to measure signals at this speed.
Unfortunately, this will leave technicians in the dark, being unable to see signal structure, which will delay diagnosis and potentially lead to misdiagnosis in vehicles which utilise the Flexray network infrastructure. In order to provide some clarity, I’ll do my best to answer some of the questions that surround diagnosis of this system.
Just how widespread is the use of Flexray? If we consider the group (known as a consortium) who were involved with developing the Flexray standard, it included Bosch, Phillips, Freescale, NXP Semiconductors, BMW, VW Group, Daimler, General Motors, Ford, Mazda, Fiat, Toyota, Honda, Nissan, PSA, Renault, Volvo. Flexray is currently fitted to a wide range of vehicles, which include BMW (1, 3, 5, 7, X3 and X5 Series), Audi (A4, A5, A6, A7, A8, Q7 and TT), Mercedes (C, S and E Class), Land Rover (various) and Volvo (various).
So how do you tell if the vehicle has Flexray? The issue with identifying Flexray from ‘under the bonnet’ is that the physical layer (for our purposes, the wiring) looks the same as CAN. It is difficult to know without consulting technical manuals or wiring diagram information for the specific vehicle in question. Also, many Flexray equipped vehicles still utilise CAN, Flexray, LIN and MOST networks on many of the sub-systems. For instance, both Audi and BMW have a combination of CAN and Flexray within the powertrain system. Telling them apart without technical information is almost impossible. This means that a vehicle which is suffering from a fault many not display useful or useable test or data values.
How can I test Flexray? Can I use the ohmmeter across the data link connector like I do with CAN? In truth, using the ohmmeter across the datalink connector has always been a very slack method of testing CAN. This is due to the implementation of diagnostic interfaces (firewalls or gateways) which separate the actual CAN from a diagnostic version of CAN. In systems which use this technique, the data link connector uses a ‘simulated’ 60 Ohm resistor between the data link connector and the gateway. In this case, the CAN proper (the vehicle side of the diagnostic interface) could be shorted to ground, having no communication, but your test at the data link connector will show a good reading of 60 Ohms.
It is possible to measure the vehicle with a meter and a scope, but the preferable option for speed and accuracy, is to use a scan tool to perform a global scan of the vehicle. Aftermarket diagnostic tools have been facing a growing challenge of how to communicate with, and interpret codes and data from all of the modules on the entire vehicle network. Poor network coverage means that you may miss (not be able to see) vital diagnostic data. Another area where the aftermarket tool is lagging significantly is its ability to display the current status of the vehicle network in a topology style. The vast majority of dealer tools perform a global scan upon initial communication with the vehicle. This technique ensures that a total vehicle state is used as a basis for subsequent diagnosis. In addition to this, the topological view can provide vital clues to the nature and location of any vehicle network issues.
But I don’t have access to dealer tools in my workplace. Am I doomed? If you are limited to using aftermarket scan tools for your diagnosis, you’ll need help in the form of an analytical technique to support your diagnostic data’s critical analysis. Technical Topics have developed a Network Fault Cluster Analysis Technique to help with just that.
The best advice is for technicians is to build their awareness of the new range of vehicle networking technologies. Attend some training, read some articles and get some hands-on research time with a modern vehicle. Build a baseline of information so that when faced with a problem, you stand a chance of differentiating between the good, the bad and the ugly. Spending some time researching Flexray, Ethernet and DOIP and V2X will pay dividends in the long run. If face-to-face learning is your preferred method, it just so happens that I know a firm which runs a very cool in-vehicle networking training course.
James is running the following courses at Technical Topics HQ in Bridgwater:
June 10th to 14th – EV Bootcamp
June 18th and 19th – EV Level 3
June 20th and 21st – VW Dealer Tool Training
June 24th and 25th – Oscilloscope Masterclass
June 27th and 28th – Peugeot & Citroen Dealer Tool Training
July 1st & 2nd – IMI Diagnostic Technician Programme
July 3rd & 4th – IMI Master Technician Programme
July 8th to 12th – Diagnostic Bootcamp
July 15th to 19th – EV Bootcamp
July 22nd & 23rd – BMW Dealer Diagnostic Tool Training
July 25th and 26th – Volvo Dealer Diagnostic Tool Training
For detailed course information, please visit: http://www.techtopics.co.uk/training-events/