Knowing how your car's "computer" works, will make you a smarter car accessory buyer.
Though motor-vehicles have changed drastically in the last 20 years, our perception of how the vehicles we drive actually function, essentially hasn't changed at all.
For the most part, we view our cars and trucks as a collection of mechanical systems. These systems work together to move the car or cool the interior or turn on the backup camera when the car gets shifted into reverse.
In the mid-80's, that paradigm began to change. Instead of a set of autonomous mechanical systems working congruently, the modern vehicle consists of a set of networked electronic systems that coordinate to make all those systems run more efficiently.
Whereas depressing the gas pedal in an old 1969 Mercury Cougar simply increased gas flow to the carburetor, which in turn forced the transmission to change gears.
Your Car's Computer—It's Really Many Computers Called Electronic Control Units
In the modern automobile, pressing the accelerator pedal communicates with the Transmission Control Module, which in turn tells the transmission exactly when to change gears.
Now, self-contained specialized computers—called electronic control units (ECU)—actually control the functions of your various mechanical systems.
There's the Transmission Control Module (TCM) we mentioned earlier. As you can infer, it controls the car's transmission.
There's an Engine Control Module (ECM), Body Control Module (BCM), Powertrain Control Module (PCM), General Electronic Module (GEM) and many others.
Each of these modules manages their specific mechanical systems. In addition, each ECU also communicates with other ECU's, as was demonstrated in our acceleration example.
Why communicate? Communication among ECUs leads to better performance by your vehicle.
When the ECM increases speed, the transmission module knows how to do this while using as little fuel as possible. The Suspension Control Module (SCM) will adjust to provide a more comfortable and safer ride.
CAN Bus—The Communication System for Vehicle ECUs
So let's take a step back to when your vehicle was a collection of autonomous mechanical systems.
The autonomous setup required more individual parts to be wired individually. Not a big deal back in the 1940's, there weren't that many electronic parts to a vehicle.
As automobile technology and designed progressed, more and more electronic systems got added, leading to more and more wiring. Automobile designers began using multi-wire looms and harnesses to manage all the electric cables.
Over time, all that wiring became impractical. Automobiles literally had miles of wire weaving throughout the frame. All that wiring also added extra weight, over 100 pounds in some instances.
Instead, engineers designed parts to be wired to individual control modules. Each control module—remember those specialize computers—would be wired to a central wiring network.
The control module would communicate via this central backbone, and manage individual parts and systems more directly. This setup prevented the need for all the wiring to connect the thousands of parts.
Engineers used a network topology called CAN Bus. They chose CAN Bus because it allowed individual ECUs to connect easily, only required one central wiring system to connect all systems, continued to work even if an ECU failed and provides a protocol infrastructure that enables very fast communication.
We won't break down all the technical specs about CAN Bus in this post. Just understand that it's the network your cars computers use to communicate and keep your car functioning.
ECUs, A Computer By Any Other Name Still Requires Updates
So essentially, technology turned our collection of autonomous mechanical systems, into a portable network of highly specialized computers.
ECUs have been programmed to function in very specific ways. Part of functioning properly includes listening for very specific signals from other ECUs.
If we swap or add an ECU to our CAN Bus network, and other members of the CAN Bus don't know how to communicate, your car may not function properly.
That's why adding a new aftermarket radio or OEM radio can cause steering wheel buttons to malfunction or your electronic climate control to freak out.
In order to maintain the harmony in your vehicle electronics system, the new equipment and the existing equipment on the network need to be introduced, and shown how to communicate.
If your vehicle originally came with no backup camera, the ECM hasn't been programmed to listen for a signal from the TCM that the vehicle shifted to reverse. As such, the ECM can't tell your new backup camera to turn on and the interior screen to switch to the backup camera feed.
If you've never taken your vehicle into the dealer for CAN Bus updates, you should do so at your earliest convenience. There can be multiple updates to your vehicles CAN Bus programming. Without the updates, your car could be performing totally different than intended.
OBD-II, Your Doorway Into the Good Ol' ECUs Club
So how do we reprogram all those ECUs on our CAN Bus so our car's cruise control button works properly?
Most light-duty vehicles utilize what's called an Onboard Diagnostics protocol to communicate with ECUs on the CAN Bus. In most cars, you can find a plug under the dash on the driver's side of the car. That's your OBD-II port.
The OBD-II port provides a physical entry point for a technician to plug into your car's network. An OBD-II adapter can be pre-loaded with specific computer code. An automotive technician would use the OBD-II port to send new instructions to your CAN Bus.
In turn, all the relevant ECUs will be notified of the new network member and how they plan to communicate with the team.
Existing ECUs will also receive new sets of instructions on what signals will be relevant from the new ECU, and subsequently how to respond to those new signals.
Now You Understand How Your Car's "Computer" Works
Wow, we just covered a great deal of automotive engineering design history in a short discussion. How will this knowledge serve you moving forward?
Understanding how your car works, will help you better understand how to keep it running at peak performance. It also helps you understand what needs to be done when something doesn't seem to be doing it's job.
It also helps you become a more informed consumer when purchasing accessories for your vehicle. Before you go out and add a bargain radio or touchscreen, you now understand the importance of knowing how it can alter the way your car works.
Infotainment specializes in replacement OEM radios and accessories. We invite you to visit or online store.