Is it a Communication Issue, Electrical Issue or Both?

Vehicle electrical systems incorporate complex communication systems that allow the many components of the system, as well as the modules that control them, to work together. These systems impact component function and control, which can result in what appears to be a faulty component stemming from a communication issue. It is no longer enough to master Ohm’s Law, know how to root out tricky parasitic drains and effectively deploy voltage drop testing to pinpoint circuit issues. Technicians must also understand how communications systems work, what their normal function looks like and how to remedy faulty communications to effectively diagnose electrical system issues. We have pulled together several resources related to this topic.

Serial Bus Primer

In this article from Underhood Service, Andrew Markel breaks down today’s Serial Data Buses: the functions they perform, how they work, the types of configurations you are likely to encounter and some diagnostic strategies. He emphasizes the need to become proficient in analyzing wiring diagrams to understand how modules and sensors are configured on the bus. He also stresses the need to familiarize yourself with the different possible bus configurations: “Being able to recognize whether the topology is a loop, star or hybrid configuration will make testing and diagnosing shorts, grounds and communication errors faster and more effective than using steps and flow charts.” It is a great introduction to these systems.

Communications as a Component of No-Code Diagnostics

In this article from Underhood Service, Gary Goms uses the case of a stalling Tahoe to illustrate a successful diagnostic framework for resolving these difficult repairs. In the article, he follows a methodical approach to pinpoint the source of the problem. In the process of his routine, he addresses communications issues related to specific components. The first action taken, in the case of this repair, was to replace the Throttle Actuator Control (TAC). While this didn’t completely resolve the issue, it was a necessary step toward the ultimate resolution. “The accurate transmitting and receiving of serial data obviously requires good circuit integrity and adequate system voltage.” Later in his diagnoses, he discusses how the Tahoe’s CPK, if compromised, fails to send the correct signal to the PCM, resulting in a stall. It is a great article on the ways communications impact components and vice versa.

Serial Bus Origins, Functionality and Diagnosis

While this article from Motor, by Dave Hobbs, is a little dated, it provides a great overview of Serial Buses: why they originated, their role in the vehicle and important diagnostic strategies related to them. He introduces the concept F.R.E.D. (frustrating ridiculous electronic device) and the four areas of concern when diagnosing failures of this type: Failure of Module Hardware, Failure of Module Power & Grounds, Failure of Bus Wiring and Failure/Limitations of Software. He addresses each area and the key things to remember related to each. He also identifies key tools in your diagnostic arsenal, such as meters, wiring diagrams, lab scopes and communication error codes. If serial bus networks are not your strongest suit, this is a great starting point to build your knowledge base.

Electrical/electronic systems and control communications are a matched pair in today’s vehicles. To successfully manage F.R.E.D.s, as Dave Hobbs calls them, a technician needs to have mastery over the entire range of issues they encounter, including communications issues where a proper signal is not being sent (or received) by a component or components. We hope these articles are helpful, whether as a refresher or as an introduction to an area you are interested in learning more about.