In the good old days, if you wanted to sound the horn, you pressed down on the center of the steering wheel. A switch just under the pad would complete the ground path for the horn relay, closing the relay. With the relay closed, the path through the horn itself would be complete and off it went!
Not anymore.
CARS participants who attended “Body Control System Diagnostics” on Monday learned just how important a role numerous control modules, all communicating together on a common network, play in carrying out even the most simple of tasks. For example, on many late model cars, the horn switch sends a signal to a body control module (BCM), or computer, that is actually responsible for controlling the horn relay. Other vehicle systems can involve multiple modules in order to complete a requested action from the driver, including such routine tasks as opening a window or turning on the headlights.
“This is a 50,000-mile overview,” says the presenter, David Talavera. “While the material is GM specific, the whole focus of the class is to make technicians aware of just how many modules are on today’s cars and how they work together.”
Talavera included information for his attendees on different communications protocols (that’s the way the computers talk to one another) used by GM products, and the differences between replacement modules that require initialization or reprogramming. He also shared information on diagnosing these systems, separating them into what Talavera calls the “physical layer” versus the “data layer.”
“The physical layer covers faults that lay in the hard configuration of the circuit…shorts, opens, etc….and how the circuit is laid out, whether it is a single wire, two wire, or twisted pair,” he says. “The data layer is the type of protocol in use…UART or GMLAN, for example.”
Talavera also stressed to participants that independent shops might find themselves at a disadvantage when diagnosing these systems unless they have the proper equipment and the proper information.
“Many aftermarket scan tools can’t access all the information or bidirectional controls the OE tool can, but every shop can access the factory information for a nominal fee,” He says. OE factory service information web sites can be linked to from www.oem1stop.com. He shared with us that additional GM factory level training is available at www.techconnect.com, with listings for live seminars and even online, at home, training modules.
Talavera hosted an earlier CARS presentation on Sunday (Hydrogen Fuel Cell Technology) and is scheduled to present another on Tuesday (Emerging A/C Technology and Service). Talavera is now a maintenance and repair product specialist for ACDelco after 20 years as an automotive technician and repair shop owner. His career as an instructor includes time at Lincoln Technical College and as an ASEP instructor at Arapahoe Community College.
