Scan Tool Help

Copyright 2023

A scan tool is a must for automotive diagnostic work today. When your 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. A scan tool allows you to read fault codes and other diagnostic information.


On most 1995 and older pre-OBD2 domestic vehicles (OBD1), 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 to find out why the light is on.

Manual flash codes were used prior to 1996 when OBD2 was introduced. Each vehicle manufacturer had their own code sequences and procedures for reading the codes. Basically, the engine computer would be put into a diagnostic mode to check for codes. If any codes were present, the computer would flash a light to display the code. Most flash codes used a combination of long and short flashes to indicate double digit numbers, and if the vehicle had more than one code, it was sometimes difficult to tell when one code ended and the next began. You also had to look up the code number in a service manual to determine what it meant.

When OBD2 was introduced on all new vehicles in 1996, it standardized common or generic code lists and definitions. Vehicle manufacturers could still have their own "enhanced" or vehicle specific codes, but all would be accessible through a common 16-pin diagnostic connector with a scan tool. The tool would display the code number and a simple description of the code.


Actron cp 9125 code reader

The most basic type of scan tool is a simple code reader. A code reader can access and display codes from your vehicle's computer. 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). Code readers are relatively inexpensive and typically sell for under $50.

A code reader can also clear codes to turn off the Check Engine light. 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 reads and clears codes. It does NOT display any sensor data or other system operating information. To read sensor and other system data, you need some type of scan tool or scanner software.

An important point to keep in mind here is that a fault code by itself does NOT tell you which part needs to be replaced. The code only tells you that a fault has been detected, not what caused it. The code serves as a starting point for further diagnosis. Many people don't understand this and assume an inexpensive code reader is all they need to "diagnose" and repair their vehicle.

Also, do not assume all code readers display all codes. They all display "generic" or "global" OBD2 codes ("P0" codes). But some do not display manufacturer "enhanced codes" ("P1" codes), or if they do, the list of codes may be limited to domestic vehicles (Ford, GM & Chrysler) and not include any enhanced codes for Asian or European vehicles.

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 with a standard OBD2 16-pin connector. Most code readers cannot read codes on 1995 and older cars or trucks because the connectors are different. However, vehicle-specific code readers are available for older GM, Ford or Chrysler applications. The same is true for BMW, MINI and some other import 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 VERY quickly, and have to be updated with new software via plug-in memory chips, cartridges or internet downloads from the tool supplier. If you are shopping on ebay for a used code reader or scan tool, make sure it will work on your vehicle, or can be updated to your vehicle.


Actron CP9670 scan tool
Innova 3040RS scantool
Actron CP9670 and Innova 2040RS are good DIY scan tools and can usually be bought for less than $100.

For advanced diagnostics on today's vehicles, a full feature scan tool is recommended. Scan tools for do-it-yourselfers can display sensor values and system data, but DIY scan tools cannot perform various system self-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, etc. This level of diagnostics requires a professional level scan tool (which are EXPENSIVE!) with bidirectional (two-way) communication capability and the proper software for accessing and running these type of tests.

Scan tools have different ranges and capabilities. Entry level DIY scan tools typically sell for less than $100. They 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. Most basic tools cannot access ABS or airbag codes. As a rule, the higher the price of the tool, the more features and capabilities of the tool.

Entry level scan tools that are sold in auto parts stores are usually designed for do-it-yourselfers, and 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 professional level scan tool or factory scan tool.

Let the Buyer Beware: DIY Scan Tools are NEVER Up-To-Date

A word of caution about all DIY scan tools: They do NOT cover current model year vehicles. In fact, most are at least 5 to 8 years BEHIND current model year cars.

Although they may not contain the newest data set, DIY scan tools will still read the common generic codes regardless of year. The area where they lag is any changes that have occurred in the enhanced or vehicle specific vehicle manufacturer codes.

The reason why most DIY scan tools are not up-to-date with current model year vehicle is because most new vehicles have 3 to 5 year waranties that cover the powertrain and emission controls. If a vehicle has a problem while it is still under warranty, you can take it back to the new car dealer for diagnosis and repair.

So if you have a newer vehicle the code files in a basic DIY scan tool probably won't include the most recent "P1" vehicle specific codes. The scan tool will read and display all GENERIC codes from current model years back to 1996, but that doesn't help you if you have a newer vehicle with a problem that only generates a vehicle specific P1 code. It may show a P1 code but if the definition of that code has changed since the last model year, the information won't be reliable. You need the current code information to make an accurate diagnosis.

By comparison, professional grade scan tools (which are a whole lot more expensive than a basic DIY scan tool) do cover more recent model years and are maybe only a year or two behind current model years. However, technicians who use these tools have to pay a subscription fee for the latest service information (which is usually updated quarterly).

DIY scan tool manufacturers claim their products are updatable so newer model year coverage can be downloaded at a later date. The problem is you can't get these updates until the manufacturer decides to spend the time and money to do an update. Even if they do an update, you may be disappointed to learn they no longer support your "obsolete" scan tool so you have to buy a new scan tool that contains updated information and capabilities.

Consequently, don't think a $100 or less DIY scan tool is a product you can use forever. They are essentially disposable tools that have a limited lifespan. Yes, it's a ripoff but short of investing in a high dollar professional grade tool and signing up for annual subscription updates, you don't have much choice.

See Keeping Your Scan Tool Up To Date for more information about software updates.


The next step up from a DIY scan tool is a Pro tool. Professional grade scan tools are much more advanced then basic DIY scan tools, and can do most of the same things an OEM factory scan tool can do. Pro scan tools have bi-directional capabilities and can run various self-tests (such as opening and closing solenoids, energizing injectors, turning the cooling fan on and off, etc.). Pro scan tools can access most modules on a vehicle, display all or most of the PIDs (sensor data, system status, etc.) for various systems including powertrain, body, suspension, ABS and airbags, and can perform relearn and initialization procedures (such as resetting the steering angle sensor after the wheels have been realigned, resetting idle speed and so on). A lot of these capabilities are not needed by the typical do-it-yourselfer, but they are a must for most professional techs.

SnapOn Scan Tools

The better tools typically have better display screens, too. These include larger LCD screens with color graphics and touch screens. 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. Some also have wireless capabilities too, with WiFi and/or Bluetooth for communicating with the vehicle, a laptop or desktop PC or printer.

Another feature that's available in many professional level scan tools is the ability to flash reprogram PCMs. Flashing a PCM with updated software may be necessary to correct a drivability or emissions issue. Flashing is often 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: Make sure the tool you buy will cover the vehicles you will be working on. Some claims can be misleading. A scan tool 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, not detailed factory codes or access to non-powertrain systems. Some pro scan tools will provide all the generic and enhanced OBD II codes but no additional codes for ABS, air bags or other systems. 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.

The starting price for most Pro scan tools is in the $3000 to $4000 range, and can go up to $15,000 or higher! The price depends on the features, tech support and application coverage.

Another cost associated with buying a professional scan tool is the cost of annual software updates. Updates are essential for keeping up with changes that occur every year. Update subscriptions can cost up to $800 per year or more depending on the vendor and what they require.

Scan tool technology is constantly changing with new models of various scan tools being introduced all the time. Our advice for shopping and comparing Pro scan tools is to visit the tool supplier websites and browse their product information and/or training videos:

Scan Tool Information & Training Videos:

Click Here to View Autel scan tool training videos

Click Here to View AutoLogic scan tool training videos

Click Here to View Bosch scan tool training videos

Click Here to View Launch scan tool training videos

Click Here to View OTC scan tool training videos

Click Here to View Snap-On Scan tool training videos


Aftermarket Pro scan tools are versatile in that they can be used on a broad range of model, makes and years. OEM scan tools, on the other hand, are dedicated tools for primary use on that vehicle manufacturer's own brand, not other vehicle brands. Most independent repair shops that service all makes/models would probably not invest in an OEM specific tool. But specialty shops (typically those who service import luxury brands) often have to buy an OEM tool because they can't find an aftermarket Pro tool that provides adequate in-depth coverage for their customer base.

Here is an excellent resource for finding vehicle manufacturer (OEM) scan tool service information. The site has direct links to each vehicle manufacturer's scan tool service information: NASTF OE Scan Tool Information.

Vehicle manufacturers are constantly updating their scan tools. Most OEM scantools are now PC-based and require an interface (cable or wireless) to connect the vehicle to a shop computer and the OEM service information website. Here is an example of GM's latest OBD interface tool, the GM MDI 2 EL-52100-AM made by AC Delco:

GM MDI 2 scantool interface tool

Product Description: The GM MDI 2 is the next generation Global Diagnostic Interface tool for both current and future GM vehicles, and extending through future vehicle protocols and architectures. It is a compact communication module with increased processing power and security that manages the transfer of data between a vehicle's onboard ECU network with an auxiliary CAN bus. The GM MDI 2 replaces the MDI introduced in 2007, for Pass-Thru programming and offers faster programming speed than the MDI.

The MDI 2 can be used to perform Pass-Thru programming on all vehicles built since 1996 and into the future. Servicing the current generation vehicles will require the diagnostic software, GDS2, Global Diagnostic System 2 running on a local PC device while the MDI or MDI 2 is connected to the vehicle. The MDI 2 connects to the vehicle via the J1962 connector using a DLC cable. Connection between the MDI 2 and the PC can be accomplished via standalone (USB) and the dealership network (CAT5).


General Motors Tech 2 factory scan tool by Vetronix

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 for late model applications may cost $5000 up to $16,000 or more!

Older legacy 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. Most of these scan tools are now obsolete and no longer supported by the manufacturer. However, they still work on the model year vehicles they were originally designed to service, so if you have an older vehicle one of these older scan tools should work fine on your vehicle. You can find older used scan tools at reasonable prices on ebay. The only drawback with buying an older scan tool is that most of these tools can no longer be updated.

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.

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. However, some will also buy one or more OEM scan tools if they do a lot of work on a particular make (such as Audi, BMW, Mercedes, MINI or VW). And they may also use a basic code reader for making quick code checks.

By comparison, aftermarket Pro scan tools cover a much wider range of makes and models (although you may have to pay extra for extended European and/or Asian coverage on a tool designed primarily for domestic makes). But although they work on many different makes and models, the software in the tool may lack some or much of the capabilities of the OEM scan tool. Certain self-tests may not be accessible. Some PIDS may be missing or unreadable. Check with the tool supplier for a detailed list of the vehicle applications it covers, and the capabilities of the tool on those applications. Some aftermarket scan tools have much better coverage than others, and some specialize in import applications.


The electrical systems on most vehicles use an onboard communications protocol called CAN or Controller Area Network. CAN started phasing in in the early 2000s, and became standard on all cars and light trucks in 2008. 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. Older scan tools that were manufacturer prior to the arrival of the CAN protocol cannot be upgraded to read the newer CAN vehicles. So if you are buying a used older scan tool, keep that in mind.

Innova 3140 scan tool

Innova 3140 CAN-compliant scan tool.


In addition to dedicated scan tools, you can also buy software that transforms a laptop or desktop PC, tablet or smart phone 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 laptop, tablet or smart phone into the OBD2 diagnostic connector 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.

Scanner software for a laptop, PC, tablet or smart phone requires either an interface cable that plugs into the OBD2 connector, or a WiFi or Bluetooth OBD connector so your vehicle can communicate with your electronic device. The scan tool software, by itself, is useless without the cable or wireless interface that connects your computer or electronic device to your vehicle. 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 USB OBD cable.

One of the advantages of using a laptop or desktop PC as a scan tool is having a large 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 17 inches diagonally, while most PC monitors range in size from 16 to 22 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 as a scanner is that it can easily be updated by downloading the latest software via the internet. This also can be done with most newer scan tools as well (using a PC as an interface with a USB cable). The updates for DIY scan tools are often free, but for professional scan tools there is usually a fee or yearly subscription to pay.

Dedicated scan tools, by comparison, are designed to be scan tools and nothing else. You cannot surf the Internet with them or check your e-mail or Facebook page. They are for diagnosing cars only. Many professional-grade scan tools have additional hardware circuitry and test leads that allow you to use the tool as a multimeter or digital oscilloscope to measure voltages, resistance and current. This is an extremely useful feature to have and reduces the need for additional test equipment.

ScanTool & Code Reader Updates:

Updated July 11, 2023

Most professional scantools now require annual software subscription fees. These fees can range from $600 to $1500 or more depending on the tool and the manufacturer. Yes, it is expensive but it is a cost of doing business today and keeping your scantool up-to-date.

The following are offsite resources for updating your scantool software and data base:

Actron Scantool Updates (by model)

Autel Scantool Updates

Bosch Professional Diagnostic Tools Software Updates

Innova Scantool Software Updates

Launch Scantool Update Service (authorized Dealer)

Snap-On Professional Diagnostic Tools Software Updates


SnapOn Vantage graphing scope

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. Many professional scan tools can simultaneously graph and display up to four different PIDs.

Some of the newest professional scan tools have software that displays only the PIDs that relate to a specific fault code. This helps narrow the list of things to look at when troubleshooting a problem. The software will also flag any PID value that is obviously out of range (most of the time, but sometimes a bad reading may not be flagged). Intelligent diagnostics is a big step forward in saving time and improving the chances of pinpointing the cause of a fault correctly the first time.

Some scan tools will also display a list of the most commonly replaced parts that relate to a fault code on a particular vehicle. This list is based on real world feedback from working technicians, and lists the parts by how commonly they are replaced. Such a list can be helpful by giving you an idea of what might be wrong with a vehicle. But the downside of showing such a list is that some users may not do the rest of the diagnosis that is needed to pinpoint the fault. In an attempt to save time, they may simply replace the part at the top of the list, or maybe some or all of the parts on the list in an attempt to get a quick fix. They might succeed in fixing the fault or they might not. Either way, it's a lazy (and expensive!) way to fix cars.

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 you blip 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.


According to a user survey of 400 technicians by iATN (International Automotive Technicians Network), the most popular scan tool form factors are as follows:

61% prefer a hand-held scan tool (name brand pro tools such as Snap-On, OTC, Launch, Autel, etc.)
28% prefer a laptop with scanner software
11% prefer a tablet with scanner software

Those who prefer a traditional hand held scan tool say the units are much faster and easier to use than a laptop or tablet. However, many of the newest professional level scan tools are using Windows-based scanner software in a custom hand held form (Snap-On Modis, Verus, Verdict, etc.).


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 ( 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."


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.

Click Here to Look up technical service bulletins TSBs for your vehicle 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.

Larrys Guide to Check Engine Light Diagnostics

Click to view the guide below (pdf file)

Larrys Guide to Check Engine Light diagnostics

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Understanding OBD II Driveability & Emissions Problems

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Controller Area Network (CAN) Diagnostics

Understanding Engine Management Systems

Flash Reprogramming PCMs

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Mode 06 Onboard Diagnostics

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