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Scan Tool Help
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A scan tool is a must for diagnostics today. When the Check Engine Light is on, you have to access the vehicle's onboard diagnostics with a code reader, scan tool or scanner software to find out what's wrong.
READING CODES
On most 1995 and older pre-OBD2 domestic vehicles, diagnostic trouble codes can be read manually by grounding or jumping certain terminals on the vehicle's diagnostic connector. This puts the powertrain control module (PCM) into a self-diagnostic display mode, causing it flash out the code via the Check Engine Light (Malfunction Indicator Lamp or MIL). You then look up the code number in a reference chart (such as DTC Code Finder) to find out why the light is on.
The problem with reading manual flash codes is that (1) they are no longer used on most 1996 and newer vehicles (one exception is Nissan), and (2) counting the series of flashes can be confusing. Most flash codes use a combination of long and short flashes to indicate double digit codes, and if the vehicle has more than one code, it may be tricky to tell when one code ends and the next one begins. So the preferred method of reading codes on older vehicles is to use a code reader or scan tool.
On 1996 and newer vehicles with OBD2, there are no manual flash codes. You must have a code reader or scan tool to read the codes.
CODE READERS
The most basic diagnostic tool is a code reader. Like a scan tool, a code reader can access and display codes from the vehicle's PCM. The least expensive models only display a number while the better ones also provide a definition (some are even bilingual and can display in English, Spanish or French).
A code tool can also clear codes to turn off the MIL. Some code readers can also display the "ready" status of various OBD II monitors (ready means the monitor has completed its self-check process). But a code reader is NOT a scan tool because it only read codes and clears codes, and maybe displays OBD2 monitor status. It does NOT display any sensor data or other operating information. So a code reader is useful for reading and clearing codes, but not for advanced diagnostic work.
An important point to keep in mind here is that a code by itself does NOT tell you which part needs to be replaced. A code tells you a fault has been detected, but it is only a starting point for further diagnosis. Many people don't know this and assume an inexpensive code reader is all they need to "diagnose" and repair their vehicle.
Also, don't assume all code readers display all codes. They don't. Some will only display "generic" or "global" OBD2 codes ("P0" codes). Others will display manufacturer "enhanced codes" ("P1" codes) but many only do so on domestic models and not European or Asian imports. Check the makes the tool covers before you buy.
Something else to check before you buy is the model years the code reader can access. Most code readers are for 1996 and newer OBD2 vehicles, and they cannot read older cars or trucks. Code readers for older vehicles are typically vehicle specific (GM, Ford or Chrysler) because the vehicles all have different diagnostic connectors. On 1996 and newer OBD2 applications (and some 1994 and 1995 models), a standard 16-pin diagnostic connector is used. This allows one tool to fit all applications.
Something else to keep in mind about code readers (and scan tools), is that the list of new DTCs and system data grows with every new model year. Last year's tool may not work on next year's models. Tools get out-of-date quickly, and have to be updated with new software via plug-in memory chips, cartridges or internet downloads from the tool supplier.
For advanced diagnostics on today's vehicles, a scan tool is an absolute must. Scan tools can display sensor values and system data, and can also be used to perform various tests such as checking the operation of the fuel pump, cooling fan(s), idle speed control motor or solenoid, EGR solenoid, A/C compressor clutch, fuel injectors, EVAP leak test, EVAP purge controls and more -- provided the scan tool is a professional grade model with bidirectional (two-way) communications and the proper software for accessing and running the vehicle specific tests.
Like code readers, scan tools have different ranges and capabilities. Entry level "generic" scan tools that cost a couple hundred dollars can read and clear codes, display the status of the various OBD II system monitors, and display basic operating data such as loop status (Open or Closed), airflow, coolant temperature, oxygen sensor outputs, throttle position and other sensor readings, and fuel trim values for diagnostic purposes. Most of these tools are fairly versatile and work on all domestic makes (Ford, GM & Chrysler), but may require additional software for Asian and/or European applications.
Entry level scan tools, especially those marketed for do-it-yourselfers, however, typically lack bidirectional communications capability for liability reasons. They may also display only a limited number of "PIDs" (Performance Information Data such as sensor values, switch status and other operational data) compared to a more advanced scan tool. Consequently, the diagnostic capability of an entry level scan tool is limited.
The more advanced professional grade scan tools, by comparison, can do most of the same things an OEM factory scan tool can do. They can access and display all or most of the PIDs (with the proper software), and they can access and run all or most of the OEM self-tests (again, with the proper software).
The better tools typically have better displays, too. These include larger LCD screens with color graphics. The tool may also have multi-channel scope function that allows data to be displayed as a graph or waveform. This makes is easier to detect certain kinds of problems that may occur too quickly to notice when looking at numerical data. Many scan tools also have a "flight recorder" capability that allows data to be captured while the vehicle is being driven, for later analysis. An add-on 5-gas exhaust gas emission analyzer may also be an option.
Another feature that's offered on some scan tools is the ability to flash reprogram PCMs. Flashing a PCM with updated software may be necessary to correct a driveability or emissions issue. Flashing may also be necessary if the PCM is replaced. The other option is to get a J2534-compliant "pass-thru" tool that serves as an interface between the vehicle's PCM and a laptop or desktop PC.
NOTE: Some claims can be misleading. A vendor may say their product or software package covers a long list of makes and models, but it may be only generic OBD II information. They may not even have enhanced codes for the applications listed. Others may provide all the OBD II codes but no additional codes for ABS, air bags or other systems beyond the engine and powertrain. Some may have limited diagnostics and not include all the factory tests or procedures. If you are not sure exactly what is or is not included, ask before you buy.
OEM factory scan tools provide full access to virtually everything, but are very expensive compared to many aftermarket general purpose scan tools (though some of the high end aftermarket tools also cost thousands of dollars depending on their features). An OEM scan tool may cost $5000 or more!
OEM scan tools include the Tech II for General Motors applications, New Generation Star (NGS) tester for Ford/Lincoln/Mercury, DRB III for Chrysler, and a list of others for the Asian and European makes.
Factory scan tools generally provide access to all the diagnostic trouble codes (both "generic OBD II" and "enhanced"), all the on-board self-test procedures, and all of the other on-board electronics beyond engine performance and emissions such as the body control module, ABS module, air bag module, suspension module, climate control module and so on. The OEM scan tool can also be used to "reset" or "initiate" a module if it has been replaced (which is often necessary before the module will function correctly)> Often this involves a special "relearn" procedure that may only be available with the factory scan tool.
The only drawback with OEM scan tools is that most (with some exceptions) are designed to only work on ONE make of vehicle, not all makes and models. Consequently, they are well suited for new car dealer technicians but not general repair shop technicians who usually work on all makes and models.
Most technicians can't afford to own a separate scan tool for each and every vehicle they work on, so most opt for a general purpose scan tool and add software and hardware to expand its capabilities as needed. Some may also buy one or two OEM scan tools if they do a lot of work on a particular make (GM, for example, or an import). And they may also have a basic code reader for making quick code checks.
. Innova 3140 CAN-compliant scan toolIn recent years, more and more new vehicles are being built with a new onboard communications protocol called CAN or Controller Area Network. CAN uses a much higher baud rate to allow faster communication between modules. Because of this, CAN vehicles require a scan tool that is CAN-compliant for diagnostics. Some older scan tools are CAN-capable and can be upgraded with new software or hardware cartridges, but many cannot. CAN will be required on all new vehicles by model year 2008, so if an existing scan tool is not CAN-compliant it will soon be obsolete.
. In addition to dedicated scan tools, you can also buy software that transforms a laptop or desktop PC, or a Palm Pilot or Pocket PC into a code reader or scan tool. Some of these offer very basic functions only while others run essentially the same software as an OEM scan tool.
The simplest and cheapest packages that sell for a couple hundred dollars or less essentially give you the ability to plug a Palm Pilot or Pocket PC into the diagnostic connector on a 1996 or newer vehicle and use it as a code reader to display and clear generic OBD2 fault codes. The better packages include enhanced codes for specific vehicle applications, and also may include the ability to display various PIDs such as sensor voltages, switch status and so on. The best software also includes graphics for displaying sensor voltages and other data.
A basic Palm Pilot usually can be purchased for $99 or less, while a more capable color Pocket PC with a larger display and more memory may cost $400 or more. All of these devices require an interface cable to connect the tool to the vehicle. In some cases, the software supplier provides the software at no charge but requires you to purchase the cable. The software, by itself, is useless without the cable to connect the tool to the car. If you are resourceful and want to save a few bucks, there are numerous sources on the Internet where you can buy interface cables separately, or kits or plans to build your own cables.
Software also is available that can convert a laptop or any other Windows-based PC into a scanner. Most require a Windows 98 or higher operating system. Like the hand-held Palm Pilots and Pocket PCs, the key here is the interface cable that connects the computer to the vehicle.
One of the advantages of using a laptop or desktop PC as a scanner is having a larger display (which makes it easier to read and can display more information on a single page). Most laptops have a screen that measures 12 to 15 inches diagonally, while most PC monitors range in size from 14 to 17 inches or larger. If you have an old PC sitting around gathering dust, you can convert it into a large display color scan tool at a minimal cost (typically $250 to $500 or less for the software, including the interface cable).
Another advantage of using a computer, Palm Pilot or Pocket PC as a scanner is that it can easily be updated by downloading the latest software from the Internet. This also can be done with some dedicated scan tools as well (using a PC as an interface). But many scan tool manufacturers (Snap-On, for example) require you to buy an update cartridge that plugs into their tool. Others want you to pay a yearly subscription fee for updates, or to continue using your tool after the initial subscription expires.
Dedicated scan tools, on the other hand, are designed to be scan tools and nothing else. You cannot surf the Internet with them or check your e-mail or auctions on eBay. But you can fix cars with them. Many professional-grade scan tools also include additional hardware circuitry and test leads that allow you to use the same tool as a multimeter to measure voltages, resistance and current. This is an extremely useful feature to have and eliminates the need for yet another piece of test equipment.
SCAN TOOLS WITH SCOPE DIAGNOSTICS
Many high end professional scan tools also have the added ability to function as graphing multimeters or digital storage oscilloscopes. Being able to display sensor voltages as waveforms makes it much easier to detect problems that are nearly impossible to diagnose any other way.
If you are looking for a multi-purpose tool that can be used as a scanner, multimeter and scope, choose one that can display more than one waveform at a time. Several units that are now on the market can simultaneously graph and display up to four different PIDs.
When a scope is hooked up to a sensor or circuit, it shows what is actually going on inside that device or circuit. Voltage is displayed as a time-based waveform. Once you know how to read waveforms, you can tell good ones from bad ones. You also can compare waveforms against scan tool data to see if the numbers agree (which is a great way to identify internal PCM faults).
A scope also allows you to perform and verify "action-reaction" tests. You can use one channel to monitor the action or input, and a second, third or fourth channel to watch the results. For example, you might want to watch the throttle position sensor, fuel injector waveform, crank sensor signal and ignition pattern when blipping the throttle to catch an intermittent misfire condition.
Using a scope does require a working knowledge of scope basics as well as the limitations of the scope you are using. Like scan tools, different scopes have different capabilities, so study and compare before you buy.
SCAN TOOL COMPARISON REPORT
In 2000, the U.S. Environmental Protection Agency did a comparison report of the major scan tools that were available at that time. The report compares the capabilities of the various scan tools. To view a copy of this report, Click Here ( the report is a pdf file).
For an up-to-date report compiled by the National Automotive Service Task Force (NASTF) on which scan tools are required for which vehicle applications, Click Here .
If you would like to read one shop's experience with scan tools and why they own what they own, Click Here
ADVANCED SCAN TOOL DIAGNOSTICS
For advanced scope diagnostics, you will want to learn how to access Mode 06 information on a scan tool (most tools that cost upwards of $200 can access Mode 06 today, but you have to know how to find it because it is not clearly marked. Mode 06 data is the raw hexadecimal code data the engine computer looks at when it runs system monitors. This is useful information to access when a vehicle is experiencing a no-code driveability problem, to verify whether or not a particular sensor or circuit is operating within its specified MIN and MAX values, and to verify a sensor or other component is working properly after it has been replaced.Information on translating and converting Mode 06 hex code for Ford and GM can be found on the International Automotive Technicians Network website (www.iatn.com). Go to the "Technical Resources" menu, then look in the Ford and Toyota sections. The Mode 06 information is in a downloadable PowerPoint presentation by Paul Baltusis of Ford Motor Company, called "An Introduction to Vehicle Networks, Scan Tools and Multiplexing."
OTHER THINGS YOU WILL NEED IN ADDITION TO A SCAN TOOL
When you buy a scan tool, don't expect to become a diagnostic expert overnight. All scan tools have a learning curve, and it takes some time to figure out what the tool will do (and what it cannot do), which PIDS and other sensor data you should be looking at when troubleshooting different kinds of faults, and what the information means.
Scan Tool Companion is a handy reference program that can help you make the most of your scan tool. The program runs from a CD on a laptop or Desktop Windows PC, and tells you which PIDs and data you need to look at by symptom, by code or by system. It also includes background reference information on engine sensors, OBD2 monitors, OBD2 emissions testing, and the operation of the engine management system. This is a "must have" reference program for any scan tool user.
Something else to keep in mind is that a scan tool by itself can't fix anything. It takes a brain to operate and use the information provided by the tool. You need to be knowledgeable about OBD2, engine management systems and sensor diagnosis. You also need access to current service information, technical service bulletins and electrical wiring diagrams. If you do not know how a sensor or circuit functions, what causes a code to set, or how a particular sensor or circuit is wired, how are you going to fix the fault?
You also can't rely on codes alone to identify all problems. Many problems never set a code. Some codes can be misleading because of the combination of circumstances that caused them to be set. Other codes may be false codes that never can be eliminated by normal repair procedures. You may have to reflash the computer to fix the problem.
The best advice here is to always check for TSBs, whether you find any codes or not. In many instances, there will be a TSB that covers the problem and will save you hours of frustration.
Click Here to Look up Technical Service Bulletins for Your Vehicle In conclusion, the more time and research you put into choosing a scan tool, the better satisfied you will be. Check with your equipment suppliers or the sources listed below for specific product models, features and prices. Spend some time on the Internet researching the various alternatives. Do your homework and you will find the tool (or tools) that are right for you.
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