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When vehicle makers began using electronics to
control certain functions, it led to vehicles being equipped with on-board
diagnostic (OBD) systems to monitor and diagnose problems. Computer-controlled
systems are found on every vehicle built today.
With the implementation of OBDII
[in the US]
1994, the number of systems capable of being accessed using a scan tool has
increased. At the same time, the amount of diagnostic information available to
technicians has also increased. Because of this, it has become more important
for technicians to have equipment capable of accessing this information and
thus, the advancement of the handheld scan tool.
The Need for Scan Tools
With technological development in today’s
vehicles, the handheld scan tool has become a necessary tool for proper
diagnosis and repair. A scan tool may be required after simply disconnecting and
reconnecting the battery on some vehicles. Some primary functions of a scan tool
include accessing and/or clearing diagnostic trouble codes (DTCs), monitoring
and/or activating system parts, uploading information, and recording data. A
scan tool gives a technician the ability to communicate with computer-controlled
systems, including the anti-lock brake system (ABS) and passive restraint
To ensure vehicle and equipment compatibility for
such things as the connector and communication procedures, the Society of
Automotive Engineers (SAE) developed standard requirements for vehicle,
equipment, and toolmakers. These standards included scan tool operation.
Standard emission diagnostic regulations, known as OBDII, were implemented
on January 1, 1996. Compliance to the OBDII regulations requires
standard 16-pin data link connectors (DLC), communication protocols for scan
tools, and DTCs.
three OBDII communications
protocols being used by vehicle makers. When using a scan tool, be sure it works
with the protocol of the vehicle. Typically, the three scan tool protocols and
the vehicles they support are:
SAE J1850VPW (Variable Pulse Width Modulation)
SAE J1850PWM (Pulse Width Modulation) (Ford)
ISO 9141 (Chrysler group, most European, most
On vehicles built since January 1, 1996, scan
tools link to a vehicle diagnostic system through a universal connection port,
which is typically located just below the instrument panel on the driver's side.
As a requirement of OBDII, the DLC must be located within 91 cm (36") of the
steering wheel, and not require any tools to access. Some DLCs may be covered to
protect the pins against damage. Depending on the scan tool being used, hooking
up to the DLC may provide the necessary power for the scan tool to operate. Some
vehicles may have connectors in other locations in addition to the required DLC
under the instrument panel.
Selecting a Scan Tool
Scan tools can be purchased either from the
original equipment manufacturer (OEM) or an aftermarket supplier.
OEM scan tools include, but are not limited
Aftermarket scan tools include, but are not
Pro Link 9000
Some diagnostic tool providers offer diagnostic
software for use with the Palm handheld Personal Digital Assistant or a laptop
Scan tool operations, capabilities, and display
configurations will vary. Because all scan tools are different, it is very
important to have the user’s manual for the tool that you will be using. To
support changes in vehicle technology some scan tools have the capability of
When using scan tools and reading repair manuals
there may be acronyms used. These acronyms have been developed by the automotive
industry and standardized by the SAE (document number J1930). Understanding the
meaning of common acronyms will help the technician with quick and complete
understanding of electronic information.
Scan Tool Procedure
When accessing information from a vehicle computer
using a scan tool:
Connect the scan tool to the diagnostic connector.
Retrieve the DTCs.
Record the data that is contained within the
vehicle computer. This will help the technician retain the DTC information in
the event the data gets lost or erased from the computer memory.
After the diagnostic information has been
Access the appropriate repair information.
Repair the affected systems as required.
Test-drive the vehicle to verify that the original
complaint is corrected.
The repairs to a vehicle, the current DTCs have to
be cleared. Typically vehicles built after June 1995 will have the DTCs cleared
using a scan tool or by doing a test-drive.
Test drives may be required to allow the vehicle
computer to verify that the problem no longer exists. Doing the test drive also
allows the technician to verify that the problem is corrected. After the
computer does a self-test during a test drive, the current code should
A test drive can be done with a scan tool
connected. Do not attempt to monitor the scan tool display while driving. Have a
second technician ride along to monitor the scan tool, or use a scan tool with
data storage capability, which allows accessing the information after the test
drive is completed and the vehicle is no longer in motion.
Depending on the vehicle and ability of the scan
tool being used, a technician may be able to monitor some systems, or turn some
electrical systems on and off.
Some vehicle systems that may be tested include
the fuel pump, ABS, engine cooling fans (both HI and LOW speed), and vehicle
computer output tests. Using a scan tool and other equipment, a technician can
perform various tests including fuel and vacuum leak tests and electrical tests
of solenoids and sensors.
Even though some tests can be done on electronic
sensors using a multimeter and other simple test equipment, this random-type
testing is not recommended. There may be hundreds of possible problem areas. The
most efficient method of identifying a faulty sensor, or a fault in a sensor
circuit, is by connecting a scan tool to the OBD connector and retrieving a DTC
that leads to the area of the problem. The DTC does not identify a failed
sensor, but a problem circuit that may or may not lead to a faulty sensor. Then,
following a flowchart in a service manual, the problem can be repaired. The
steps in the flowchart usually require simple tests on the problem circuit. Many
of these tests can be done with the use of the scan tool.
To make sure that the vehicle has been fully
tested through all possible scenarios, a drive cycle can be performed. A drive
cycle may also be done with a scan tool connected while the drive cycle is
performed. Some scan tools will even guide the technician through the steps of a
drive cycle for the particular vehicle.
After the drive cycles have been performed, if the
malfunction indicator lamp (MIL) is on, a scan tool is the best tool to
determine why the lamp is lit. The drive cycle may or may not set a DTC, turning
a MIL on.
Scan tools may also help with record keeping. Scan
tool data can be printed out and can serve as documentation as part of the
In review, with vehicles of today being equipped
with multiple computer controlled systems, having scan tools available and
knowing how to use them allows for an efficient repair process. In some
situations, repairs may not be possible without the use of a scan tool.