(Printed in the Journal
of The Alliance of Automotive Service Providers, AASP)
Why are cars such a mystery today? Why have “advances” in technology made
cars more difficult to diagnose and repair?
I don't have any one magic bullet answer, but lack of service information
is perhaps the greatest issue. The problem lies in the lack of information
regarding vehicles' on-board electronic control systems, or, what used to
be called, "solid-state" controls.
Look up solid-state in a dictionary, and you will find an interesting definition.
It usually says something like, “electronic devices, like transistors or
crystals, that control current without the use of moving parts, heated filaments
or vacuum gaps.”
Although a term from the 1960s, every computer module today is still a
solid-state device. To many, solid-state is any box with attached wiring
that has an internal circuit board. It is the box where the magic happens
– the box where electronic decisions are made. It is the box with the sticker
that says, "Do not open. No user serviceable parts inside."
Automotive technicians today are expected to quickly test, diagnose and
repair these solid-state devices. Unfortunately, only a small amount of information
is offered about these devices on modern-day automobiles. If were lucky,
the auto manufacturer will offer a printed wiring diagram to aid in testing.
If we are really lucky, the wiring diagram's wire colors will actually match
the colors of the wires on the car we are testing.
All too often, the wiring diagram for the car doesn’t match the colors
of the car's wiring. At that point the technician is, in essence, blindfolded,
not knowing which wires are supposed to carry what amount of voltage. Even
when access to a correct diagram is available, the logic of the solid-state
device is usually unknown. Auto manufacturers rarely print the exact strategy
of these devices. Often the manufacturers will lay claim that the actual
operational logic is "proprietary information." Today’s medical industry
faces similar challenges. Often, pharmaceutical advertisements and
literature will state that a medicines “method of action is unknown.” Just
like automotive electronics, there is a vacuum or black hole in the information.
How then can a technician repair a device when he or she does not know how
This is where many shops will have to guess and plug in a new module, which
generally cannot be returned. When faced with this dilemma, some shops
will refuse to work on the car altogether. Then the customer is left searching
for another shop that will take a stab, guess or "shotgun" repair. Take
the following examples that both our shop and Motor Age's Richard McCuistian
have recently encountered.
- A customer with a 1997 Jeep Grand Cherokee has the
engine computer replaced to correct a performance problem. The customer comes
back the next day stating that the keyless entry transmitter is now inoperative.
The service manual advises reprogramming the transmitters through a scan tool
connected to the vehicle. After performing this procedure the transmitter
is still inoperative. The technician places a call to a diagnostic hotline.
Now the Chrysler specialist at the hotline asks if the computer was recently
replaced. Guess what the cause of the problem is? The customer had not used
the new computer enough. After a new computer is installed in a Grand Cherokee,
the keyless entry feature will not be activated until the engine has been
started 20 times. Valuable shop time and tools wasted. The technician is left
looking like a dummy. Why is this information not in the service manual?
- A 1998 Dodge Durango comes in with the complaint that
the four-wheel-drive (4WD) service light is on. This is strange because the
truck is actually a two-wheel-drive (2WD) model. A Chrysler service bulletin
is found that addresses the problem. The bulletin states that the problem
is caused by a defective Heating/Ventilation/Air Conditioning (HVAC) module.
Now the customer pays to have the $265 module replaced, but the 4WD light
still remains illuminated. A call to the diagnostic hotline reveals
more information: The battery must be disconnected for 30 minutes. Then the
new HVAC module has to be configured with a scan tool. During the configuration
the technician enables the air temperature display function. Finally, the
4WD light is gone but now one of the dash climate control buttons won't stop
flashing. Another call is placed to the diagnostic hotline. First the advisor
asks if the air temperature function was enabled during programming. Then
the advisor asks if this car has the overhead compass and temperature display.
Finally the advisor tells the technician to buy a second HVAC module. Enabling
the temperature display on a car without the overhead compass/temperature
feature causes this failure. Once enabled it cannot be reversed. Now the shop
has to replace the $265 HVAC module for free. Again, how is the technician
supposed to know this diagnostic strategy if it is not written down somewhere?
- A 1988 Buick Century comes in with an overheating problem.
A technician drives the vehicle with a scan tool connected to view the computer's
datastream. The technician is interested in monitoring the engine cooling
temperature reading and the on/off command information for the engine cooling
fans. On the road test, the technician notices that when the computer turns
on the cooling fans several datastream lines have scrambled unreadable data.
This scenario is normally a hallmark symptom of a faulty computer. The computer
is replaced, but again the same datastream lines are unreadable when the
cooling fans are on. A call to the scan tool manufacturer reveals that the
car's computer is fine. The manufacturer's representative advises us that
they are aware of this glitch that occurs when their brand scan tool is hooked
up to 1988 Buick automobiles. They are going to correct it in a future software
update cartridge that we can buy when it’s available.
- A customer requests another keyless entry transmitter
for a ’92 Oldsmobile Cutlass Cieria. The $99 transmitter is special-ordered.
Now the fun part: Try programming it to work with the car. To program a
new transmitter, the procedure in the ’92 Cieria service manual says to:
1) Turn the ignition off. 2) Jump together terminals A and B of the Assembly
Line Diagnostic Link (ALDL) connector under the left-hand dash. 3) Press
unlock on one transmitter. 4) Press unlock on the second transmitter. 5)
Disconnect the jumper wire. After trying this procedure six times, the new
transmitter still does not work. On a hunch, the technician looks up the
same procedure for a 1991 Ciera. The procedure for the 1991 is totally different.
That procedure says to: 1) Access the remote entry connector, (green in color),
in the trunk under the left rear wheelhouse trim. 2) Put a screwdriver between
the two terminals in the connector to join them together. 3) Push any button
on the first transmitter. 4) Push any button on the second transmitter. 5)
Remove the screwdriver and reseat the trunk trim. It worked on the ’92 Ciera.
Nevertheless, why did the technician have to use a 1991 procedure on a 1992
car? Why did the 1992 procedure not work? On what car does the 1992 procedure
Unfortunately, in the modern world of solid-state controls, some progression
will always lead back to some regression.