by Hib Halverson
Corvette is one of
most sophisticated cars GM makes. Depending on model year and options,
computers may control the engine, transmission, shock absorbers, climate
control, sound system, supplemental inflatable restraints, anti-theft
devices and door locks. They also enhance braking and traction on poor
copyright 1997 by Shark Communications
NO USE WITHOUT PERMISSION
All this has made
servicing our cars more complex and expensive. However, the complexity
and cost would be many times what it is, if it were not for diagnostic
equipment. Visit a Chevrolet dealer and you will be amazed at the
line-up of high-technology devices service technicians have to address
computer-related problems. The proliferation of diagnostic aids have
made service easier and cheaper because finding the problem is a less
time consuming process. But, it wasn’t always that way.
I remember the early
years of on-board computers. Back then, service technicians at dealers
and independents, where all whining the same sob story, "I hate
these %^&* computers! Heck, you think I was fixing a !@#$ rocket
ship, not a Corvette."
If dealer techs were
crying the blues, imagine what it was like for the do-it-yourselfer
(DIY) working on computers in the early ’80s. Back then, diagnostic
equipment specific to servicing on-board computers was a rarity at
Chevrolet dealers and generally not available to DIY enthusiasts, at
Thankfully, that sad
state of affairs doesn’t exist, today. We may choose from a variety of
diagnostic products limited only by budget and knowledge of use. There
are four general types: 1) reasonably-priced, basic devices that do not
process information from on-board computers, 2) "scan testers"
that cost more, but offer a higher level of diagnostic aid because they
process information 3) software-based scan testers or scan tester
enhancements that work on a personal computer, 4) premium scan testers
and other, up-level equipment.
The mother’s milk of
automotive on-board computer troubleshooting is the diagnostic trouble
code (DTC). Any Corvette computer, or powertrain control module (PCM),
has some level of self-diagnostic capability such that, if it detects a
problem; it stores data about that problem in its memory. This data is
encoded in strings of either two or four digits. All ’80-’95 cars
send two-digit DTCs, ‘96-up cars send four-digit codes and ’94s and
’95s may send both, depending on the type of equipment being used to
Almost all Corvettes with
computers have a diagnostic link connector (DLC) which is kind of an
electronic gateway to the PCM and a Corvette’s other on-board
computers. The DLC can be used to send commands to the PCM telling it to
transmit codes. All 1982-’93 Corvettes have 12-pin DLCs. Base-engine
’81s have 5-pin DLCs; however, ’81s with L82s lack a DLC because
they do not have computer controls. Corvettes built for sale in
California during model year 1980 (MY80) have a peculiar system (see
sidebar) without a DLC.
All ’81-’93 computer
cars send DTCs if one connects the DLC’s PCM "diagnostic" or
"test" pin to its ground pin, turns on the key, but doesn’t
start the engine, and watches the "check engine" or
malfunction indicator light (MIL) flash. Service manuals contain
information that decodes the flashes.
The ’94-’97s have a
16-pin DLC. MY94/’95 LT5 PCMs, because they lack OBD-II capability,
will transmit codes via MIL flashes; however, ’94-’97 LT1/4 and LS1
PCMs have: OBD-II capability, no PCM diagnostic terminal and do not
transmit codes via the MIL.
All 81-’97 Corvette
PCMs also transmit DTCs, along with other information related to the
on-board computer system, over "serial data" lines which have
a pin or, in later years, pins in the DLC. To read this serial data you
need a scan tester or other computer device that connects to the DLC and
is intended for automotive diagnostic use.
Got all this? There will
be a test, later…just kidding.
the Basics, Please
expensive tools covered in this article are "code access
keys." These fork-like, metal stampings join pins-A and -B of a
12-pin DLC. They are marketed by MascoTech, Mac Tools, Wells
Manufacturing and others. They are better than a jumper wire because
they solidly link the pins. A device that accomplishes the same task in
a more foolproof manner is the "Code Scanner" from Sunpro. It
makes the pin-A to-B connection by locking to the connector body. An
added attraction of Sunpro’s device is that, on ’89-’93s, it can
command display of antilock brake system (ABS) codes.
On 1989 or later
Corvettes, the DLC accesses DTCs from on-board computers other than the
PCM. In fact, by 1991, there were seven different readouts available,
each flashing codes via either lights on the driver information center
(DIC) or on ’91-’96 speedometer displays. Each of these diagnostic
modes can be entered by grounding a particular pin of the DLC and, in
some cases, making DIC key panel entries. Knowing which pin to ground,
which key to press and how to decode light flashes or read the
speedometer takes experience or time sifting through Service Manuals.
Plus, you need to have the right code access key or must make a jumper
While a detailed
discussion of on-board computers other than the PCM is beyond the
scope of this article, readers working on MY89-’96 cars and who want
to read the memories of these other computers, as well as those of ’89-’93
PCMs, ought to consider purchasing the Performance Choice "Code
Analyzer." This piece of equipment can ground most of the ’89-’96
diagnostic pins. The user connects the Analyzer to the DLC, selects the
proper pin to ground via a rotary switch and a two-position, model year
switch, turns on the key with the engine off and codes are read with the
appropriate flashing light or the ’91-’96 speedometer. The Code
Analyzer comes with a manual covering all diagnosis modes used on ’81-’93
cars. Performance Choice extends support back to MY81 with an optional
adaptor and extends partial support up to MY96 with a different adapter
and a manual supplement. Performance Choice’s Code Analyzer is a great
DIY product and the only non-serial, diagnostic device that can read PCM
codes on all Corvettes from MY81-’93, ZR-1s to MY95 and all non-PCM
codes from MY89-’96 cars.
If there is a confusing
aspect of the Performance Choice Code Analyzer, it’s the final few
words of the last sentence above. If you are considering this device for
use with a 1994, ’95 or ‘96 car, understand that the "User’s
Manual," included with the so-called "1994-95 OBD-II
Supplement," states in several places that the device will enable
display of PCM codes from ’94-’96 Corvettes. Reality is that
this update does not support OBD-II, at all. In fact, the Code
Analyzer with the Supplement will not enable display of any
codes from ’94-up PCMs except those of LT5s. With LT1/4 engines,
after the 1993 model year, it only enables display of codes from
the chassis or body computers. To access PCM codes after 1993, a scan
tester is required.
If you are
troubleshooting the ignition system of a computer Corvette, there may be
diagnosis procedures that instruct you to test spark output. This is
done with a spark gap tester, a specialized type of spark plug with a
ground clip that you clamp to a good engine ground. They are available
from a number of sources. You connect the plug wire and crank the
engine. If the spark can jump the calibrated plug gap, then you know the
ignition is capable of spark. KAL Equip, the service-trade arm of the
Actron Corporation which makes Sunpro products for the consumer market,
markets an adjustable spark gap tester (P/N 4617) that functions with
all types of ignition systems use on Corvettes, even non-computer cars.
Even though computers do
the "thinking", old-fashioned vacuum operates some of the
sensors and control devices, such as EGR valves, emissions canister
purge valves, MAP sensors, dashpots, delay valves and so forth.
Troubleshooting may require a temporary source of vacuum, typically a
hand-operated vacuum pump, available from a variety of tool
manufacturers. I use the Neward Enterprises’ Mityvac Silverline pump
(p/n 4000) because of its ease of operation, rugged construction and
detailed manual. Other hand pumps are available from Sunpro and Mac
A very common device in
on-board computer service is the digital multimeter (DMM) which measures
voltage, resistance, current, engine rpm, dwell angle and duty cycle.
They come in a variety of flavors from cheap, swap meet junk up to
high-end stuff. Several steps up from the swap meet level and a great
value is the Sunpro CP7678. It’s user-friendly, reasonably-priced and
has functions many DIY’s need.
procedures require a DMM with a minimum of 10 megohms input impedance
for accurate measurement. If you need that feature, a more up-scale unit
will be required such as the Mac Tools ET18DMM or the Performance Choice
17048. Both the Mac and Performance Choice units are standouts. The Mac
is built by Fluke, the famed test instrument manufacturer and is built
to service-trade standards.
Another handy item is the
Sunpro Sensor Tester Plus. Computer Corvettes have many sensors that
send data to the PCM. The Sensor Tester Plus is a stand-alone device
that easily checks many of them. It has the required 10meg. impedance
for oxygen and knock sensor testing, comes with a detailed manual and is
an excellent companion to Sunpro’s non-10meg-ohm DMM.
A volt-ohm-milliammeter (VOM)
is similar to a DMM, but has an analog display. VOMs are valuable in the
solution of intermittent problems (or just "intermittents")
some of which exist so briefly that most digital units won’t indicate
because they can’t react quickly enough. However, a brief voltage
spike will cause a VOM needle to jump. You may not get an accurate
reading, but you will know something is changing. That alone can be an
important diagnostic clue.
Our favorite VOM is the
Simpson 260 which is well-suited for Corvette service use because of its
accuracy and durability. Less expensive VOMs are available from sources
such as Radio Shack. If you’re on a budget and don’t need the
milliammeter function; Sunpro sells a low-cost, analog, volt-ohmmeter
Performance Choice makes
a number of specific, wiring harness patches that allow easy DMM or VOM
of testing oxygen sensors (O2S), manifold absolute pressure (MAP)
sensors, manifold air temperature (MAT) sensors, throttle position
sensors (TPS), knock sensors (KS), coolant temperature sensors and idle
air control (IAC) motors. These patches can be used with any DMM,
however certain tests require a unit with 10meg. input impedance. The
patches are available individually or in "kits" according to
model year and we love the "kit by model year" approach to
packaging this stuff. It makes trying to select the right test harnesses
as simple as looking in the Mid-America catalog for your model year and
Often overlooked, because
it’s been around for half-a-century or more, is the test light or
continuity tester. Though discount stores sell test lights, we prefer
better-quality units from Mac Tools (p/n ET125C) or Sunpro (p/n CP7845).
Both have a replaceable lamp, an impact-resistant housing, a
spring-protected cable and a heavy-duty ground clip. Some diagnostic
tasks may find a conventional test light inadequate. Many PCM circuits
run at 5 volts and may not illuminate a 12-volt test light. The
solution, in that case, is Mac Tools’ "Mac Light" circuit
tester (p/n ET120). This unit works on as little as 3.5 volts and uses
LEDs to indicate a ground or a hot source.
It is likely that the
Corvette in question has electronic fuel injection. Diagnostic work may
involve fuel pressure readings and injector testing. Fuel pressure
gauges specific to EFI are available from Kent-Moore and other sources.
K-M markets Chevrolet dealer service tools and has a gauge for ’85-’97
port fuel injection engines (p/n J34730-1A) and another for ’82-’84
Cross-Fire (dual throttle-body) injection engines (p/n J29658-D). You
may also need a device that momentarily energizes an injector while you
read fuel pressure or voltage drop. Injector testers are available from
Kent-Moore (p/n J39021) and other sources.
I use Kent-Moore’s Port
Fuel Injection Diagnostic Kit (p/n J34730-E). It contains the port-fuel
pressure gauge, the Injector Tester along with other items needed to
diagnose EFI on all 85-up Corvettes.
Corvette PCMs take
cooling system temperature into account when setting the fuel and spark
schedules used to run the engine. Cooling systems on Corvettes built
since the mid-’80s not only run at higher temperatures but sometimes
don’t have the extra capacity we saw in ’60s and ’70s models.
Consequently, they are often running closer to their design limits. That
in itself is not a problem; however, these two situations make it
important for your car’s cooling system to be operating efficiently.
If you suspect a cooling system problem, you may want a diagnostic
device that can directly read coolant temperature and run a system
pressure check. I have experience with two different brands of this
equipment. Both can assist in diagnosing problems with thermostats,
temperature sensors and electric fan operation. Additionally,
information gained with either of these tools can help pinpoint coolant
leaks, cracks in the block or heads and failed head gaskets.
The first is Neward
Industries’ Cooling System Retrofit Kit (p/n 4510) intended for use
with its Mityvac hand-operated pump, discussed earlier. Adding this kit
to a Mityvac allows you to pressure test a cooling system via an adapter
that connects to the pressure cap mount. If you don’t have a Mityvac,
but do have a source of air pressure and want cooling test capability,
KAL Equip has its Cooling System Analyzer (p/n 2967) that performs the
In addition to adapters
for pressure testing, both the Mityvac and KAL kits include a dial
thermometer one can use to measure cooling system temperature at the cap
mount. Both adapters allow temperature measurement while the cooling
system is under pressure via a test "port" into which you can
insert the thermometer probe without pressure loss.
Ever had an engine noise
you can’t track down? For example, ’85-’93 Corvettes sometimes
suffer from an anomaly called "fuel-line hammer." The noise
sounds kind of like a valve lifter that needs adjustment, but actually
comes from fuel pressure fluctuations caused by the opening and closing
of the fuel injectors. The fluctuation sets up a resonance in the fuel
rails and flexible fuel lines near the engine that, mainly at idle, is
audible from inside the car.
The point, here, is you
may need some kind of listening device to avoid misdiagnosis of fuel
line hammer or to help you track down other engine noises. In the old
days, there were industrial-strength versions of a doctor’s
stethoscope; however, today, we have electronics. KAL Equip makes a
nifty, Electronic Stethoscope (p/n 2563) that is perfect for listening
to injectors, fuel rails, valve covers and other noisy engine parts for
Another traditional tool
you may want in a modern diagnostic situation is a timing light. Spark
schedules of most 1980-or later Corvette engines are
computer-controlled, but 1980-’91 engines, except LT5, used a
distributor and required an initial advance adjustment. To check that
initial advance or to read the spark advance curve without a scan
tester; you need a timing light.
With ’92-up engines, a
timing light is unnecessary because timing is not adjustable and there
are no marks. A weird exception to this rule is the LT5 which, in spite
of timing that can’t be adjusted, has timing marks…go figure.
"dial-back" timing lights, through an internal microprocessor,
allow the user to determine a given spark advance by 1) turning a dial
until the timing mark on the balancer aligns with the TDC mark on the
front cover’s timing scale, then 2) reading the value to which the
dial points. Standard timing lights, ie: no dial-back, can check initial
advance, but for them to read advance requires the balancer to either be
degreed or fitted with a timing tape. Many good timing lights are
available; however, be careful about shopping strictly for price. Some
inexpensive lights have trouble triggering accurately above 4000 rpm. If
you are going to check advance curves, you may need a light with stable
triggering above that rpm.
There are two units we
looked at for this story. Both performed well in our evaluation. The
first was a non-dial-back light from MSD (p/n 8990) that is popular with
many racers and has been in our shop inventory for several years. We
also tried a KAL Equip dial-back light (p/n 4165) that is unique in that
it uses a digital display rather than analog and it reads engine speed
as well as spark timing. Both of these units: have all-metal cases, have
metal inductive pick-ups that won’t melt if inadvertently touched to
an exhaust manifold, are capable of stable triggering up to 8000 rpm and
are 12-volt powered via a set of battery clips.
A scan tester,
"scanner" or, more properly, a "hand-held diagnostic
computer" is a microprocessor device a little larger than a
portable cassette recorder. It’s powered by the car battery and
connects to the DLC. It "scans" engine computer operational
data and displays it on a small screen. Scan testers are operated by a
simple keyboard. Software is usually in plug-in cartridges covering a
specific manufacturer’s vehicles. While simple PCM diagnostic
procedures with any ‘81-’93 Corvette are possible without a scan
tester; advanced service work, high-performance development or any work
with ’94-up PCMs requires one of those pieces of equipment.
The most basic scanner
operation is reading trouble codes. To do this, connect the tester, turn
on the ignition key, select the tester’s DTC function and codes appear
on the screen. Another basic feature is a "clear codes"
function. This eliminates temporarily removing the PCM fuse or
disconnecting the battery to erase DTCs once repairs are complete.
The most valuable scan
tester ability is "snapshot memory". This helps solve
intermittents by saving a block of PCM data present at the approximate
time the intermittent occurred. The user "plays back" this
data, looking at what the computer was doing during the period of time
covered by the snapshot. Often, this play back contains valuable clues
we DIY service techs can use to fix our Corvettes.
All scanners have a list
mode that displays PCM data in real time. All read at least two,
user-selectable data parameters and some read more. Even when your
computer-equipped Corvette is running fine, you’d be surprised at the
stuff you’ll learn just by having someone drive while you scan in the
A price leader in the
scan tester market is MPSI’s "Pro-Link 9000." The Pro-Link
is half the price of other scanners making it very attractive to those
on a budget. MPSI achieves this through emphasis of basic features and
sale by direct mail. The unit has an LCD display that shows four lines
of data. MPSI’s GM software cartridge covers ’81-’95 powertrain,
body and chassis computers.
The OTC "Monitor
4000 Enhanced" is quite popular amongst independent repair shops
and has many of the primary scan tester functions listed earlier. It
costs more than the MPSI, but includes software for Corvette chassis and
body computers along with that for, ah…foreign makes including Ford
and Chrysler. OTC software is divided into two ranges. One spans MY81-93
the other spans MY89-96 and includes OBD-II capability.
We prefer the TECH-1A
scan tester. In service with Chevrolet dealers since 1985 and made
available to DIYs in 1990, the "T-1" was designed and is
manufactured by the Vetronix Corporation of Santa Barbara, California to
meet a GM specification. About 80,000 T-1 and approximately 600,000 T-1
software cartridges are in use around the world. With ’81-’95 GM
powertrain software, cables, adapters and manuals it costs about $1500.
I have seen it street-priced as low as $1300. It can be purchased from
Mac Tools or NAPA stores.
A plethora of software is
available for the T-1. In addition to the standard GM powertrain
cartridge needed for engine diagnosis, there are cartridges for chassis
and body computers, an "all-in-one" powertrain cartridge that
supports vehicles from all three Detroit manufacturers along with other
TECH-1s offer basic
scanner operations along with bidirectional abilities that give the
tester temporary control of PCM functions for diagnostic purposes. A few
of these operations are: injector balance tests on ’94 or later LT1s,
LT4s and ’90-’95 LT5s, tests of the LT5’s secondary fuel system
and, with a variety of Corvettes, control of idle speed, EGR valve, AIR
pump operation and reset of "fuel trim" values.
There are T-1 options,
such as 12-volt-powered "TECH-1 Printer" which connects direct
to the tester and prints the data list or snapshots on an adding machine
tape. There are software cartridges for chassis and body computers.
Another cool option is
the "Functional Test Director" (FTD) cartridges. GM designed
features into the PCMs of ’86-’91 Corvettes that allow a T-1 with an
FTD to run automated tests on a variety of engine computer functions. At
the end of the sequence, you’re presented with results from each test.
If there is a serious problem, testing is terminated and the scanner
alerts you of the difficulty.
All TECH-1s can be
upgraded. The original T-1 can be upgraded to the T-1A level. Either
unit can be upgraded with the OBD-II capability necessary to service
1996 or later Corvettes by adding Vetronix’s "OBD-II Application
Kit" which consists of an interface adapter, a specific OBD-II
software cartridge and an instruction manual.
The TECH-1 has been in
production for 12 years, an unheard-of lifespan for a computer device.
It is a credit to Vetronix’s outstanding hardware and software design
that the same basic tester supports all MY81-’97 GM vehicles with
computers. We asked Vetronix spokesperson Jason Alexander about the
TECH-1A’s future and he told us, "There are a huge number of T-1s
out there and the unit continues to sell well. Vetronix will continue to
develop TECH-1 software on an annual basis for at least the next five
years and probably longer."
Of the scan testers
discussed, only TECH-1 is GM-validated, uses GM-validated software, is
bidirectional and has the FTD option. Only the T-1 and the OTC Monitor
4000 Enhanced support the OBD-II features of ’94-’96 Corvettes.
Right at the time this
article was posted on the Web, the Actron Manufacturing had entered the
scan tester market this fall with an entry-level unit aimed at DIYs.
Actron spokesperson, Bruce Heath, told us just before post time that
this new piece of equipment, the Sunpro CP9110, has a four-line display
and will work in the data list and snapshot modes. It supports ’84-’95
Corvette PCMs and will support the ’82 car if VIN data is entered as
if it were from an ’84. The Sunpro is intended to be list-priced at
about $475.00 for the tester and a GM software cartridge. Undoubtedly,
street prices maybe lower. A future, extra cost option maybe OBD-II
support. At the time this buyer’s guide was posted, Actron was only
selling the unit direct, however, Bruce Heath told us that within 4-6
weeks, it will be on the shelves at mass-market retailiers that carry
Actron’s SunPro brand.
Corvette can Talk to your PC
If you own a PC with an
Intel 286 or better processor, you have additional Corvette diagnostic
options. For automotive service, a laptop is desirable as it’s tough
to drag a desktop machine around on a road test. However, if a desktop
is all you have; get an extension cord and haul it out to the garage. At
least, you can run the program while the car idles in the shop.
Diacom is a software-based scanner that reads powertrain data and has
basic scan test functions. Though it was intended to run under MS-DOS,
it is compatible with what Bill Gates’ considers his gift to mankind,
Microsoft Windows 95. However, Diacom is not compatible with
Windows versions 3.xx and earlier. The current release version of Diacom,
2.83, fully-supports ’82-’93 Corvettes and supports non-OBD-II
functions of ’94s and ’95s. With an optional, five-pin DLC adapter,
support is extended back to computer ’81s.
Diacom has some
advantages over hardware devices. Because a computer screen has more
area, it displays more data in list mode. Also, during our evaluation, I
discovered that when connected to certain PCMs, Diacom reads specific
data parameters that scan testers do not. While some of these additional
parameters may be of little value in service work, they could be of
interest to one doing vehicle development. Another advantage is that, in
snapshot mode, Diacom samples data at faster rate than some scan
testers. If the intermittent you are solving is of short duration,
Diacom might detect it whereas some of the hardware devices may not.
The uplevel, Diacom-Plus
sells for $579 has all standard Diacom features and adds: 1) more
sophisticated snapshot ability with additional memory and trigger
options and 2) a line-graph mode that displays three, user-selectable
data parameters. If you want to perform any engine management system
development work, Diacom-Plus is the way to go and in some cases may be
a better choice than a scan tester due to the ease in which it stores
data on the PC’s hard drive.
Both Diacoms have
limitations: 1) They do not support ’96 or later Corvettes; however
Rinda Technologies is developing an upgrade that will and it may be
available by the time you read this story. 3) Due to differences in how
the PCM transmits engine speed data over the serial data link, Diacom
will not display engine speeds over 6375 rpm when connected to a ’90-’95
LT5. 2) They do not support chassis or body computers. 3) They are not
compatible with a few older, 386-based laptops using oddball chip-sets.
Generally, these machines were price leaders. If you have questions on
compatibility, resolve them with Rinda Technologies, and 4) the cable
that connects the laptop to the DLC is too short for road test use. A
"keyboard extension cable," available at most computer stores,
Bottom line? If you already
own a laptop PC and you’re working on a ’81-’95 Corvette; for
all the stuff it does and its $299 price tag; "standard"
Diacom is an outstanding value for the DIY service technician.
For someone with both a
PC and a TECH-1, a useful program is a scan tester enhancement
called "Techview." Distributed by Vetronix through Mac Tools,
it allows a PC to act as a display for a TECH-1. It is available in two
versions, one that runs under DOS and another for Windows 3.x, NT and
95. In its list mode, Techview shows up to 42 data parameters
simultaneously and in color, if you have a color monitor. Techview also
has three graphic modes: bar-chart, line-chart and overlap line-chart.
It saves snapshots to a PC’s disk drive which makes it valuable to
those wanting to store data for future reference.
Where Techview really
shines is in its bar chart mode. Four user-selectable engine parameters
are displayed in real-time, vertical, color-bar form for a revealing
picture of how different engine management data interact.
Both the OTC and the MPSI
testers also transmit data for display or storage on a PC. For the
Monitor 4000 Enhanced, OTC has a program called "E-Z Event
Plus" that functions like Vetronix Techview. The MPSI Pro-Link,
requires no additional software but transmits only in the list mode.
Top of the Line
We promised you
diagnostic equipment for your Corvette from mild-to-wild. Well…now you
get wild. We talked earlier of the lowly test light. Would you like a
fully-computerized test light? If so, Mac Tools quenches your
thirst for high-tech with their "Logic Probe" (ET130). This
unit uses a microprocessor-controlled, triple-LED set-up to test
continuity of DC circuits running at as little as one volt. It also
tests the AC or pulsed-DC output of a variety devices such as
distributor pick-up coils, crankshaft and camshaft position sensors or
ABS speed sensors. The Logic Probe can even test some electrical
functions of fuel injectors while the engine is running.
Mac also sells the ZR-1
of digital multimeters. Manufactured to Mac’s specifications by
Tektronix, this piece of equipment (p/n ET332) has outstanding accuracy
for an automotive DMM. It’s rugged, has a high-impact plastic case and
is surrounded by a rubber boot will take any punishment you can dish
out. It has all typical DMM functions along with the ability to test
diodes, measure AC voltage, capacitance, injector pulse width and
During our evaluation of
the ET332 we were impressed with some of its unique, high-tech
automotive features. It’s the only DMM we’ve seen that senses
voltage spikes you normally could only measure with a VOM. This
"peak hold" feature senses spikes as short as one millisecond.
It’s, also, the only unit we’ve seen with a digitally-generated,
"pseudo-analog" bar graph that reads simultaneously with the
numeric display. Some clever electronics allow the Mac ET322 to measure
injector pulse width. It has a data recording function which, like a
scan tester’s snap shot mode, assists in solving intermittents.
Controls are intuitive and to save the battery, it even shuts itself off
after 15 minutes of inactivity. If you want the finest DMM available to
advanced DIYs, the Mac Tools ET332 is your baby.
More high-end, "technogeekery"
is Vetronix’s second-generation scan tester, the "Mastertech,"
which could be described as: TECH-1…only more so. It uses T-1
software, offers all T-1 functions, uses the convenient and familiar T-1
interface and, with simple installation of a optional "daughterboard,"
is OBD-II compatible. Like other Vetronix equipment, it’s built to
tough, dealer service standards and is available from Mac Tools.
Use Mastertech in its
"enhanced" mode and you have a truly amazing, hand-held
diagnostic computer. I loved its 3"x3" display that shows
either: 16-lines of user selectable data in list or snapshot modes, six
data parameters in bar-graph mode or two in line-graph mode.
Another Mastertech option
is the "Enhanced Diagnostic Lead Set" that includes some
optional test leads, an interface box and two instruction manuals. It
adds an oscilloscope mode that can be used to graphically represent the
electrical operation of sensors, actuators, injectors and ignition
systems. While use of an oscilloscope would be considered an advanced
diagnostic technique, the Vetronix Mastertech offers adequate waveform
display ability at a fraction of the cost of a dedicated oscilloscope.
For those inexperienced in using waveform display as a diagnostic tool,
Vetronix adds a very intuitive, on-line help program called the
"Waveform Assistant" that has a library of example wave forms.
For instance, suppose you want to see how the passenger side O2S is
working on a ZR-1, but you don’t know what an ideal O2S waveform
should look like. The Mastertech’s Waveform Assistant is always there
to show you.
After comparing their
performances in a diagnostic road test situation, I preferred the
Mastertech over a color, 486DX2 laptop running Diacom. Only get 16 lines
of data can be displayed at a time vs. 30, but in a road test situation;
Mastertech is easier to set-up and use and you still can select
on-the-fly which 16 data parameters you want to display. Another
advantage is that the Vetronix Mastertech has software for all on-board
computers in all MY81-’97 Corvettes including those with OBD-II.
If you’re wallet runeth
over, you’re starting your high-end, diagnostic tool box from scratch
and you’re looking at Diacom-Plus and a whiz-bang Pentium laptop to
run it on; consider the Mastertech instead. It’s a more capable, less
complex and less expensive package. The Vetronix Mastertech is
leading-edge stuff and one of the most advanced scan testers on the
market at this writing.
The newest piece of
diagnostic equipment of interest to Corvette enthusiasts goes with the
newest Corvette, the C5. The GM Tech 2 "Hand-Held Diagnostic
Service Tool", was introduced in February of 1996. The result of a
two-year development, it’s manufactured by the Hewlett-Packard Company
under a contract with the GM Service Technology Group (STG). By the fall
of last year, most Chevrolet dealers had at least one T2 and, at the
start of the 1997 model year, it was declared an "essential
tool" for all GM dealers.
STG chose not to make a
Tech 2 available for us to test, saying that only experienced service
personnel can operate the unit. Additionally, we contacted
Hewlett-Packard with a similar request, but they did not reply at all.
Nevertheless, we bent our rule requiring equipment covered in this buyer’s
guide be evaluated by our staff because T2 is one of the diagnostic
devices for Corvettes. Like the TECH-1A, it will eventually be available
to DIYs. Perhaps, at a later date, we can do an in-depth analysis of it.
For now, suffice to say
that manufacturer specifications indicate that the new GM tester
surpasses the Vetronix TECH-1A in diagnostic power but falls short of
Vetronix’s Mastertech, our benchmark for high-end scan testers. The
Tech 2 displays 11 vehicle data parameters simultaneously, more than the
T1’s two, but less than the Mastertech’s 16. The T2 uses a 32-bit,
16-Mhz processor compared to the Mastertech’s 16-bit/10-Hhz and TECH
1A’s 8-bit, 2-Mhz chips. T2 memory is 10 Megabytes compared to the T1’s
optional, 1 Mb. The new GM unit and the Mastertech are of similar size,
shape and weight. Like Mastertech, T2 has a larger display screen and an
enhanced keyboard with programmable keys. Unlike the Mastertech, the
Tech 2 was designed under some stringent cost constraints. To meet those
goals, hardware shortcuts were taken which make the Tech 2, in spite of
a speedy central processor, not as strong a tester in the
service-diagnostic environment as it could be. In fact, we hear reports
from the field that GM’s dealer network is not unified in their
acceptance of the Tech 2. Perhaps that will change as time goes on.
While the Tech 2’s
software may eventually backdate to the 1992 model year, the unit will
not accept T1/Mastertech software cartridges because GM and H-P adopted
the "PC Card" system for software storage. During the
development of the Tech 2, H-P had difficulty with the learning curve of
automotive diagnostic software. Interestingly, GM turned to the Vetronix
Corporation, the manufacturer of the TECH-1A and a competitive bidder on
the Tech 2 contract, for assistance. For the last couple of years,
Vetronix has had a dozen people working in Detroit developing T2
Beginning with the 1997
model year, dealer-specific, recalibration software is only available
for the Tech 2. Vetronix will continue to develop new T1/Mastertech
software for aftermarket sale until at least 2001 and probably longer
but without the recalibration feature. For pre-’92 Corvettes,
the TECH-1A remains the scan tester of choice for GM dealers and
STG tells us that the
Tech 2 sells to GM dealers for $1885.00, a price that is only a few of
hundred dollars more than the TECH-1A. It is possible that the price to
go up when the unit is eventually made available to third-party users.
The time at which GM and H-P will release the Tech 2 for sale to we DIYs
has not been determined.
diagnostic equipment is useless if you have no service data. The advent
of computer-controlled engines has made service manuals indispensable.
The best stuff comes from GM’s Service Technology Group (STG). To
prepare this article, we used the 1995 and 1996 Chevrolet
Corvette Service Manuals. Non-factory service manuals, such as those
available from Haynes for some Corvettes, are desirable for their lower
prices and coverage of a span of model years. However, to get the price
down, non-factory manuals are condensed and because of that,
occasionally, data is omitted. Nevertheless, when confronted by cosmic
price tags for factory manuals, Haynes books are an attractive value.
Books on general engine
computer subjects are also available, such as the excellent, How to
Repair & Modify Chevrolet Fuel Injection, published by
Motorbooks International or Automotive Computer Codes and Electronic
Engine Management Systems from Haynes’ Techbook series.
GM Service Technologies
Group (STG) distributes training publications to the general public
through MascoTech. Fundamentals of Computer Command Control (CCC),
and, if you use a TECH-1, the Tech-1 Handbook are outstanding
references. Additionally, if you are working on an older computer car
and don’t have a factory manual, STG’s 1981-1986 Computer Command
Control Performance Diagnosis is a great resource. If you are
interested in learning more about oscilloscopes in automotive service,
STG publishes an outstanding book, Engine Performance Testing,
that contains a large quantity of instructional material on that
Lastly, both Wells
Manufacturing and Actron, discussed in the first section of this
article, have video tapes available detailing the use of their
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