MOTOR Magazine

A MOTOR Magazine Newsletter
April 20, 2017

Contributed by Bob Chabot
Look Who’s Talking!

Verifying network integrity is essential to modern diagnostics

“As vehicle systems continue to become more electrified, their communication architectures are increasing in complexity," explained Wally Mouradian, a DENSO Corp. trainer. "Understanding network topologies, verifying their integrity, and knowing how to efficiently diagnose them have becoming essential ‘must haves’ to providing service and repair to new vehicles today. That’s only going to ramp up in the future. ‘Will you be ready?’ is the question.”

MOTOR spent a day with Mouradian at the 25th VISION Hi-Tech Training & Expo held last month. During his presentation, GM Network Diagnostics and Module Reprogramming, he shared some of his expertise regarding vehicle communication network diagnostics.

The complex code that comprises network messages means a lot to engineers and scan tool manufacturers," Mouradian advised. "Technicians don't have to review or understand that code; they just have to be able to discern whether messages have been sent and received as intended, because a simple yes or no is often a pointer toward if and where to begin network diagnostics." (All images — Wally Mouradian / DENSO Corp.)

Take the Time to Become Familiar with Network Topologies
"Think of topology as being a map or layout of a vehicle’s communication landscape, with networks the information highways on that landscape. Vehicles today typically have a number of different but interconnected networks in their onboard communication architecture — commonly known as network topology. But be aware, more networks are coming that are faster and more complex. They will not only require a change in the underlying architecture (e.g. Ethernet), they will also impact how you diagnose and resolve problems.”

Each type of network — CAN, LIN, LAN, Keyword, MOST and others — use a unique language, called a protocol, to send, receive and act on those messages. Each utilizes voltage to propel complex data via coded messages between modules, actuators and sensors positioned throughout a vehicle.

Besides the embedded action or command, these messages also include code that identifies where the message came from, its destination and the state of health of modules and other network elements. For example, where a technician may see a U2038 diagnostic trouble code (DTC), an automotive engineer will see much more information in that code.

Mouradian explained that networks can have different designs that hint at the shape and how elements on the network interact (e.g. loop, star, ring, etc.). Networks can also feature a series or parallel design, or a combination of both. Note also that automakers often tweak a certain type of network and rename it with a unique proprietary name — which can make it confusing for technicians working on multiple vehicle brands.

He cited General Motors (GM) as an example. In addition to many other protocols, GM uses two types of CAN (controller area networks) on many of its vehicles. One is the CAN High network, for which signals toggle over a 2.5 to 3.5 voltage range; the other is CAN Low, which toggle over a lower 1.5 to 2.5 range. On a labscope, the signals for each mirror each other and provide a redundancy benefit that can be helpful during diagnosis.

Most technicians know that splice boxes in wiring schematics are junctions where wiring from various modules come together, which eases testing. Newer vehicles more frequently use gateway modules, which essentially connect modules in much the same way. But gateways can also connect different networks and are able to translate data messages in one protocol to another. They also send faster messages because only the data requested is sent.

First Things First
“I'm all about diagnosing efficiently — whatever and wherever the root cause of a communication problem originates,” Mouradian emphasized. “As the electrification of vehicles proliferates, this competency is necessary to making successful repairs. In particular, being competent in network diagnostics will soon be the differentiator between making a complete repair or just getting close.”

“Technicians need to be aware that the root cause of a problem may reside in the network itself rather than a specific system, module or connection. An unaware technician who jumps right to hooking up a tool to scan all modules could be chasing ghosts or taking the long way — adding labor, and possibly unnecessary replacement parts. For instance, sometimes a message isn't received by an addressed module (e.g. due to a short to power or a short to ground), or it is otherwise corrupted (e.g. a U1000 ‘no communication’ DTC). Being able to recognize these and other network situations and proceed to a successful diagnosis and complete fix is becoming a necessary competency.”

Mouradian then identified three challenges, by way of questions, to help technicians self-assess their readiness for network diagnostics:

  • Can You Truly Apply a Sound Understanding of Electricity Basics? — It's not enough to just have book knowledge about electrical theory; technicians must increasingly be able to readily apply it to vehicles. Mouradian said he’s seen many instances where a technician who has good book knowledge cannot read a wiring diagram well enough to determine how different networks are designed to operate, let alone whether the network might be the problem.
  • Can You Use Tools and Conduct Tests Properly? — Book knowledge of electricity basics, diagnostic tests and associated tools isn't enough. Despite the wide range of tests and associated tools that are available to technicians, Mouradian emphasized that whatever test or tool is used, what matters is that technicians must know when, where and how to use them. From a tool perspective, he finds breakout boxes and labscopes to be two of the better tools to see who's talking on a network or why communication isn’t happening. He acknowledged that many technicians don’t use these. But those who rely on digital volt ohm meters (DVOMs) to diagnose are using a tool that simply cannot keep up to the speed of a network. Problems can slip through the cracks.
  • Do You Gather Enough Information First, to Justify the Diagnostic Path You Choose to Pursue? — Too many technicians start testing, even though they have no supporting evidence to do so, Mouradian noted. Trying to fix the car without understanding what is truly wrong leads to effects, rather than root causes, being treated. Those vehicles never get fully repaired until they end up in a shop under the eye of a technician who understands electricity and network diagnostics, not just how a tool operates.

Mouradian used many network case studies to walk attendees through the information-gathering approach to determine the most likely diagnostic path, supported by real evidence, to follow toward a solution and fix. These included network circuit faults due to a CAN High short to ground, CAN High short to voltage (i.e. power), CAN Low short to ground, CAN Low short to voltage, opens and others.

Network Issues Often Boil Down to Shorts to Ground or Power
“Consider this scenario,” Mouradian posed. “Have you ever encountered a vehicle with multiple DTCs on multiple modules? If so, how long did it take you to resolve the issue(s)? If you're like many technicians in this situation, too darn long.” Hold that thought.

"Customers pay you for your applied knowledge and expertise," Mouradian stated. "You need to be able to sell diagnostics confidently and perform them efficiently, even when networks are involved. To do that, you need to have a plan that you use consistently that allows you to gather enough information to support starting down the most likely network diagnostic path."

Mouradian's shared his approach to gathering supporting information, before even beginning a diagnosis. It involves six steps:

  • Conduct a customer interview.
  • Visually inspect the vehicle.
  • Research technical service bulletins and other resources.
  • Road test the vehicle.
  • Factor in known good experiences with similar vehicles similar and situations.
  • Based on the information gathered, determine the most likely diagnostic path.
  • Mouradian shared two examples of applying book knowledge and experience to network diagnostics. Here are two of them:

    • Four Digit Network Communication "U" Codes Fall Into Two Major Groups — Generic (aka global codes) have a "0" as their second digit to indicate they are common to all makes and models of vehicles. Examples include the codes that are required for basic emissions fault diagnosis. In contrast, enhanced (aka manufacturer-specific codes) have a "1" as their second digit to indicate they are unique to a particular vehicle make or model. These special codes were deemed necessary by the vehicle manufacturers so they could provide additional diagnostic information beyond the basic list of generic OBD II codes for all kinds of faults, not just emissions-related faults. To answer the challenge he posed earlier, Mouradian stated, "If just one or more DTCs on any module or on multiple modules was a U1300, U1301 or U1305, then the root cause of the issue is an intermittent short on the network circuit. Had you known that, your diagnostic path and labor would have been much more efficient.”
    • Did You Know the Last Two Digits of a DTC Point toward the Affected Module? — For instance, U1064 refers to the body control module; U1017 to the powertrain module; and U1041 to the brake control module. When a U code is set in one or more modules, the last two digits of the U-code point to where the problem is — either in the module pointed to, or in the wiring leading to it. If it’s the wiring, the issue may be a short-to-power, short-to-ground or an open.

    In the near future, everything on vehicles is going to operate on a network," Mouradian shared. Verifying the integrity of onboard communication networks, especially with the implementation of telematics, autonomous driving and more robust security is making network diagnostics a must-have competency.

    Verifying Network Integrity is Growing in Importance
    “Technicians often miss network circuit fault issues that are caused by a short-to-ground or a short-to-voltage because they don’t start at the beginning,” Mouradian advised. Similar to ensuring the battery supply is good before walking down an electrical circuit when performing a voltage drop test, technicians need to check first that the integrity of the network is good rather than jumping to scanning modules and pulling codes. Chasing what could be costly ghosts — time, labor and parts — is not efficient; it may not be effective either.”

    “In the near future, everything on vehicles is going to operate on a network," Mouradian concluded. "That's why network diagnostics is quickly becoming a must-have competency. Fortunately, aftermarket training is available to help shops and their technicians ante-up. It will help you learn how to focus on what is going to give you the most amount of information for the least amount of effort. It will also help you understand how to leverage information-gathering to better diagnose network issues. That’s an investment that will pay you back many times over."

    [Editor's note: Visit for the latest diagnostic and service insights.]

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