Electronic Accessibility

Electronic Accessibility

As electronics and computer controls advance in technology, the real issue for the aftermarket is the ability to repair these systems.

When you hear the sound of distant thunder and it’s followed by a sudden ear-splitting crack of lightning, you know that the storm is moving closer to your own backyard. Unfortunately, some people in the aftermarket hear the distant thunder and think it’s only a minor change in the weather, another new development in electronic engine management technology, if you will.

Others hearing the same thunder are beginning to think about body and chassis computers and how this technology may be putting the aftermarket technician at a major disadvantage in trying to perform what used to be very commonplace repairs, such as repairing a power window or diagnosing a malfunctioning windshield wiper motor. The crack of lightning reminds us that we not only must be able to communicate with these module-operated devices in order to diagnose them, we must also have the electronic accessibility so that we can reprogram the replacement modules to fit different chassis configurations.


Electronic accessibility, of course, is the core issue in dealing with modern engine, body and chassis control electronics. Beginning in 1996, auto manufacturers began using engine computers that could be updated by re-flashing or reprogramming their operating instructions with data available only through the auto manufacturer. In all cases, this work had to be sent back to the dealership. Currently, an independent shop can buy an aftermarket scan tool equipped with the software needed to communicate with an auto manufacturer’s website. Access to the website is by subscription, and can be rather expensive depending on the nameplate.

Editor’s note: For more information on flash technology, see this month’s feature Flash! Reprogramming Vehicle Components.

But programmable electronics has gone far beyond the confines of the engine compartment. Many of the 2005 model-year vehicles, for example, will be equipped with numerous computers and electronic control modules that operate virtually every mechanical component in the body, chassis and power train system. To better illustrate, think about inserting a key into an ignition lock. Instead of the key turning a conventional lock cylinder, the key operates an electrical switch that commands the power train control module (PCM) to activate the starter and crank the engine. Other than giving the command to start, the driver has no control whatsoever over the engine cranking process.

The issue for the aftermarket, of course, is repairing a system like this when it fails. This and systems like it require scanner-based diagnostics which means, in the simplest of terms, that a technician must use a computer to diagnose another computer.

Worse still, the aftermarket technician must program the replacement computer or control module to work in coordination with the dozen or so other modules located throughout the vehicle chassis. To program the module, the technician must be able to electronically access the OEM’s website to make the module work in coordination with the other modules. Sound complicated? Well, it is, especially for the aftermarket shop that typically services a combination of domestic and import vehicles.


For aftermarket parts distribution, the challenges created by electronic accessibility are profound. Think of it for a minute: for the past 30 years, the aftermarket has thrived upon making mechanical and electromechanical replacement parts for most popular vehicle applications. In other words, the aftermarket supplies duplicate throttle cables to replace original throttle cables. It supplies switches to replace original switches. It also supplies the relays and solenoids that these switches operate.

Now, let’s step into the 21st century. The throttle cable is being replaced by an electronic "drive by wire" system that uses a potentiometer connected to the throttle pedal. The potentiometer or "pot" indicates throttle position by supplying a variable voltage signal to the power train control module (PCM). This signal is processed by the PCM into a command that tells a stepper motor located on the throttle shaft to open the throttle. As voltage increases, so does throttle opening.

Why are auto manufacturers adding all of this rocket-science technology to the family car? Actually, the reason is very simple. By controlling throttle opening with a computer instead of the driver’s big toe, the computer can open the throttle at a predetermined rate in order to facilitate smoother automatic transmission operation, and improve fuel economy and reduce exhaust emissions by eliminating unnecessary fluctuations in the throttle plate.


The most revolutionary part of body control computers and their receiving modules is that, in contrast to relays and solenoids, they can actually "think" their way through a problem by using electronic logic. Let’s look at what happens when Mom loads the kids and groceries in the family minivan. First of all, vans are designed to transport kids and groceries. Groceries aren’t a problem, but kids can be because they love to experiment with gadgets like door handles.

In the "old days," kids could unlock doors and fall out of the vehicle. Today, as soon as the BCM senses a speed signal from the vehicle speed sensor on the wheels or in the transmission, the BCM locks the rear hatch and the doors on the van. In fact, the BCM can be programmed to unlock the rear doors and hatch only when Mom puts the transmission in park or when she actually opens her driver’s side door. The safety combinations are endless because they can be programmed into the control module’s electronic memory. Of course, if the van gets involved in an accident, the module must act in an entirely different way, which we’ll cover later.


As one might suspect, the data now being communicated by these systems is so voluminous that the current communications protocols between computers and modules have become completely inadequate. If you want a good comparison, imagine an old-time telephone operator working at normal speed. Then double the number of phone calls she must connect at her switchboard. Then quadruple them. Then quintuple them. At some point, the operator and switchboard are working so fast making connections that nobody has time to actually talk to anybody else.

Beginning in 2004, some domestic and import models started using the controller area network (CAN) communications protocol that will enable these on-board computers and modules to "talk" to each other in a much faster, more sophisticated manner. In simple terms, the engine, automatic transmission, anti-lock brakes, door lock system, lighting and other safety-based systems will be communicating with each other via the CAN system.

For example, the wheel-speed sensors in the anti-lock braking system may be coupled via computer with the stepper motor on the throttle body. If the wheel-speed sensors detect wheel spin, the engine computer may automatically reduce the throttle opening to gain traction even though the driver has floor boarded the throttle pedal floor.

And, using our example of Mom and the kids taking the family van to go to the grocery store, a more speculative illustration of inter-module communications would be a vehicle getting into a collision, which deploys the air bags. Sensing that the air bags are deployed, the air bag module waits a few seconds and then commands the body control computer to unlock the doors, roll down the windows and unfasten the seat belts so the passengers can exit the vehicle or so that rescuers can pull them to safety. The CAN protocol is currently making this type of multi-tasking between various computers both possible and practical.


Clearly, aftermarket parts suppliers face a challenge in dealing with module-controlled operating systems. Even a simple component like a power window motor may contain a small electronic module that must be programmed to take electronic instructions from a vehicle’s body control computer.

My first encounter with electronic accessibility occurred early this spring with a malfunctioning door and window lock on a 2003 Chevrolet Suburban, in which I found out that a faulty door module would have to be programmed by the dealership shop according to the VIN of the vehicle itself.

Currently, this doesn’t pose a problem because there’s not that many of these vehicles on the road. But, as these systems proliferate, an independent shop may well find itself buying the OEM scan tool and subscribing to an OEM website in order to program or "flash" each component module so it will communicate with the engine or body control computer.

The major issue is, of course, whether this capability will be made available to the aftermarket shop at an affordable price. If not, the independent repair market will continue to yield ground to the dealerships, and aftermarket distribution will suffer accordingly. Today we hear the thunder. Tomorrow the storm may well be taking place in our own backyard.

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