How
B
i
id
i
irect
i
iona
l
l
Computer
Controls
by Steve Bodofsky
www.atra.com
Affect Your Diagnostic
Strategy
B
y now it should come as no
surprise that many of today’s
vehicle computer systems are
far more complex than those of yester-
year. You’re no doubt aware that nearly
everything in today’s cars is controlled
by one of a series of computers.
And not just the engine and trans-
mission: the suspension, steering, seats,
dashboard, braking system, heating
and air conditioning, and much more
receive their cues from one of a series
Scan Tools: They Aren’t
of little black boxes. communication between the comput-
If these systems were all complete- ers… bidirectional communication that
All the Same
ly independent of one another, those allows the computer systems to share One of the great promises of OBD-
cars would be buried in a web of wir- input data and control systems in uni- II was that diagnosis would now be uni-
ing, with each wire providing unique son. Digital data streams between the versal. The terms, the codes, and even
information and control between a sin- computers using a single pair of wires. the computer signals would be the same
gle component and its computer. from one manufacturer to the next.
The main problem with that —
How It Affects You
They lied.
beside the difficulty in finding the right That’s all really interesting, and Oh, sure, the basic codes and terms
wire — is that many of the vehicle I’m sure it’s very important to the are the same. And any OBD-II scan tool
control systems require a certain level engineers who build the cars, but how will read the basic OBD-II computer
of integration; that is, they have to work does knowing about those bidirectional system codes and data. But that’s as far
together to provide the most effective systems help you diagnose them? Does as the universal stuff goes.
level of vehicle control. the bidirectional control system have From there, every manufacturer
For example, you turn the A/C on. any real effect on diagnosis? has its own data streams and propri-
The computer first raises the engine Yes, it does. In fact, there are four etary functions for its vehicles. And
idle speed before it considers energiz- basic areas of diagnostic strategy that for all but the most basic diagnoses,
ing the compressor clutch. In some are no longer the same as they were just you need access to at least some of that
cases it may adjust the ignition tim- a few years ago: data.
ing, because of the additional load the 1. Scan Tools How can you get it? The manufac-
compressor places on the engine. All to 2. Diagnostic Data turer’s scan tool will provide you with
create transparent operation of the air 3. Circuit Diagnosis full access to everything the computer
conditioning. 4. Logical Diagnostic system can deliver. But some of those
To provide that integration — and Procedures scan tools can cost well over $5000. So
avoid the web of wires — today’s man- Let’s take a brief look at each of buying every manufacturer’s dedicated
ufacturers network the various comput- these diagnostic challenges, and see scan tool is probably out of the ques-
ers. This allows the computers to “talk” how bidirectional control systems can tion.
to one another, sharing information and affect your diagnostic decisions. If there’s one manufacturer that
basing their control decisions on a com- makes up a large percentage of your
mon set of inputs. repairs, you might want to consider
They do this by using a network of buying their dedicated scan tool. But
32 GEARS January/February 2010
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