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Automotive Diagnostic OBD2 Scanner

Updated on March 21, 2011

A Professional Diagnostic OBD2 Scanner

Variety of uses within OBD II vehicles: Diagnosing for fault repairs - Emission testing - Monitoring engine performance - Individual component testing
Variety of uses within OBD II vehicles: Diagnosing for fault repairs - Emission testing - Monitoring engine performance - Individual component testing

Increased Roles of the Diagnostic OBD2 Scanner

Using the diagnostic OBD2 scanner as a tool for repairs

Modern engines have become so complex electronically that it is sometimes quite a challenging task knowing where to begin when a fault indicator lamp on the instrumentation panel goes on. This is even made worse on an OBD II engine when somebody tries to tackle these faults without using a compatible diagnostic OBD2 scanner. This really doesn't make sense, as ultimately the warning light needs to be cleared from the system's memory with this particular diagnostic tool. Most complex systems, when broken down into smaller categories will be easier to work on. A good example can be when dealing with the engine emissions system. Emissions can easily increase or even sky-rocket when something is faulty in the engine. The problem can be from a bad O2 sensor to a mechanically worn engine and anything in between. Diagnosing with an appropriate tool like the diagnostic OBD2 scanner or OBD2 reader will make fault tracing easier, even if the actual fault or faulty component is not revealed directly by the tool.
When the fault code is retrieved from the OBD's memory, the next step - if using a cheap reader instead of a quality scanner is to find the code meaning on the booklet or CD supplied with the reader. The fault code or codes results should fall under one of two possible categories: direct or indirect fault.
A direct fault is when the fault indicates a bad component. This should be verified independently by monitoring and testing the component for voltages, resistance and it's performance in relation to the rest of the system.
An indirect fault is when the fault shows up as a sectional part of the system. This pinpointing will be useful for further analysis by only focusing on that particular section, instead of the complete system.
Finally when the repair is completed the fault can be cleared and the vehicle should be tested again too see if that particular fault, or any other new fault will appear after the repair was done. Older or high mileage vehicles can suffer from this symptom when repairs are done. This is because the software data generated after the repairs were done will start conflicting with the older parts data - which was previously compensated through the engine management system.

Using the diagnosticOBD2 scanner for emissions testing

Emission test centers are now using the second generation OBD diagnostic software where applicable for the vehicle's emissions test. This is not only faster, it is more accurate as there is a much less margin for error, unlike the tailpipe tests. Old traditional tailpipe testing is quite a long process and there are many variable factors which need to be considered by the tester for the test to be successful. In the US, vehicles manufactured from the beginning of 1996 are all equipped with the OBD II software systems, as this became a mandatory specification through the EPA (Environmental Protection Agency). As each state differs in its legal emissions requirements, the OBD2 emissions test can be the only test needed, or it can be a combination of both old and new testing. This only applies for vehicles from 1996 onwards which have the OBD II system as original equipment from the factory.

The emission tester virtually uses the same type of OBD II compatible hand held scanners found at good reputable mechanics or engine technicians. Any vehicle being sent for a quality service before the test can be assessed prior the test. This will show up any troubles or emerging faults which could be repaired before the test - this way the official test sheet will come out clean and no re-tests need to be taken.

Most emission test failures will have one, or more common faults usually found on failed vehicles. These faults usually are one or a combination of the following:

  • Misfiring Evaporative System
  • Catalyst Monitor
  • Heated Catalyst
  • EGR System
  • Fuel System
  • O2 Sensor
  • O2 Heater Sensor
  • Secondary Air System
  • Comprehensive Component
  • A/C Refrigerant
  • System's Eleven Monitors

Any vehicles being emission tested must have these two points below functional and untempered so the test can continue:

  1. Functional ‘Check Engine’ Illumination which goes on when every time vehicle is started and goes out after a few seconds - Any blown out illumination bulbs for the Malfunction Illumination Light 'MIL' or ‘Check Engine’ is an instant failure. No electronic tampering devices are allowed on this circuit.
  2. Diagnostic Connector present and attached to the factory allocated position - The OBD II connector must be present and ready to accept the scantest. The vehicle must pass the OBD II parameters’ scantest.

Further details on this topic can be found on the Role of the OBD II Software and System. Mainly the OBD I differs from the OBD II because certain features, parameters and requirements became standardized in OBD II.
Previously in OBD I each manufacturer set up their own specialized, but not standardized hardware and software programing. This created confusion for the main dealers and specialized mechanics, as manufacturers sometimes did updates and changes even from one model to another. At that time, manufacturers main concern was to meet and possibly exceed the EPA requirements. Once those goals were met, nothing else really mattered to them.

Difference between OBD I and OBD II

The most important changes in the OBD II system were introducing common platform characteristics which were the same in all vehicles, regardless of make and model. A common standardized 16 pin plug was introduced and the generic codes became the same in all software systems. This move was essential so that more qualified mechanics, including the main dealers could use the same diagnostic OBD2 scanner for all OBD II compliant systems. This not only reduced the amount of dedicated factory scanners, thus reducing equipment costs, but it also helped in keeping one common system, meaning there was less hassle when working on different vehicles. The only slight leeway is that manufacturers can add extra manufacturer codes, without supplementing them for the generic codes, just to further improve their system.
This system has also expanded through foreign attachments known as OBD interfaces. One such system is the CAN (Controlled Area Network) system. This was first introduced by the German company Mercedes Benz, around 1992 in the automobile production of for their outgoing models. This technology had at least two known benefits at that time which were reducing the amount of wires found in the vehicle's harness; this first reason also gave the second benefit of less unladen weight for the finished vehicle. Some wires and circuitry were substituted for modules which could connect through a network, using far much less wires. This has led to much greater developments throughout its production life, from 1992 till today. Vehicle safety circuits like ABS, SRS (airbag), seat belt pre-tensioners, stability control, cruise control together with other comfort and luxury equipment like automatic climate control, in-car entertainment systems are all functioning through various modules which connect through a serial data bus which gathers the communications between other modules. This system has become mandatory from 2008 on all US vehicles. European vehicles will become fully complied in a few years.

Emission regulatory information is an ongoing process which is always being updated from time to time. It is a very vast and interesting subject and can be quite challenging on vehicle manufacturers. This will help us citizens live in a healthier environment. Vehicle ownership, as well as technical details on the emissions subject can be found from the official place where these regulations are being established and monitored. There is no doubt that it's the best and safest resource you can get on the subject. There you'll find legal regulatory limits and their implementations for a particular model year. Knowing and implementing their rules will keep your vehicle’s emissions requirements in the legal limit, which in turn will also help us all live in a less polluted world. There are also some guidance tips to keep your vehicle in top condition. The biggest and most influential bodies are the US Environmental Protection Agency (EPA) and the European Bureau as the Fédération Internationale de l’ Automobile (FIA).

Something which I have found on these hub pages is an article on 'Spark Plugs'. There is a link on my page below in the relevant link section, which I strongly suggest you take the time to read. Very informative and also relevant for OBD II engines, as most people ignore such items on newer engines, just because they have much less wear through the optimized engine management system. Such parts still have to be changed periodically according to the vehicle's service manual, even before if the vehicle is being used in harsh environments or over-enthusiastic driving conditions.

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    • profile image


      4 years ago


    • profile image

      OBD II Scanner 

      8 years ago

      Hi Diehard,

      Thanks for your true and sincere comment. When buying from such Auto store depots and without mentioning any brand names, it is best if you have your vehicle tested by someone competent beforehand. Typical scenario examples are like your own personal mechanic/auto technician or yourself if you have access to a diagnostic scanner and obviously are mechanically inclined.

      This way through further diagnosis you can ensure if the part is the real culprit, and MOST IMPORTANTLY if it was caused through natural wear or because of other malfunctions which are deteriorating the part.

      And it is useless if you buy your own diagnostic scanner, unless you know how determine what is actually causing the real fault codes, or faulty parts. This should be done through what we call "Reversal Diagnosis" of the part's core function.

      Typical example: If engine is found to be lean on fuel there are many various possibilities, even after getting the fault code/s, which may also include a faulty part (not just symptoms). The best way to go is using the Reversal Diagnosis, starting from the end of the fuel system and checking your way backwards throughout the fuel system circuit until the circuit finishes. That would be the fuel itself, (is it contaminated or diluted in some way?), fuel pump voltages and pump resistances next, check that all fuel (inlet, outlet and return)lines are dry outside but free from clogging particles, fuel pressure regulator, injector electrical connections, injector voltages and so on.

      Hope this helps you out and anyone else in a similar situation. Diagnostic scanners and code readers are fine to help you out, and is a "near must" on all modern engines because of the complexity in modern electronics, unlike traditional mechanical systems. But again, with that said they will have little to no use if someone using them is just barely capable of understanding the engine principles in general.

    • profile image


      8 years ago

      Mostly clerks and salesmen of Autoparts as Advance Autoparts and Autozone, are people without qualification for using any kind of Scanner. Those greedy Corporations are swindling the public making billions selling parts that "Mickey Mouse" scanners "suggest"....If you ask a copy in writing to the salesmen of any of those Autoparts they will never show up a piece of paper...90% of the possibilites you will spend hundred dollars in non-refundable parts, and still your car will be failing or broken. Solution? Go to a real Mechanic Shop. Of course you should pay the diagnosis, but they will give you on writing the results and you can complaint (even you can stop of make a payment) if after to change the parts, it didn't correct the problem ....When you buy an Oxygen Sensor in Advance Autoparts, just because "the scanner suggest it", you can't get any money back if the diagnosis was inaccurate.

      Those Stores pay extremely low salaries so you will never see an ASE technician working with.....Trust me, the Scanner is not really free, because at the end, you finish buying an expensive part without guarantee that it's the right part.

    • OBD2 Scanner profile imageAUTHOR

      OBD2 Scanner 

      9 years ago

      Hi Candy,

      Thanks for your interest in my site. I will contact you asap through email.

    • profile image

      candy zheng 

      9 years ago

      contact candy for sample test

    • OBD2 Scanner profile imageAUTHOR

      OBD2 Scanner 

      9 years ago

      There are handheld testers for old classic cars which operate all mechanical, but not as just one unit (one tester for virtually all fault detecting parameters) like the Diagnostic OBD2 Scanners / Readers.

      Simple examples are the timing handheld strobe light, thermo reader gun (heat temperature readers) and so on.

      So if you're looking for just one tool that caters for all troubleshooting faults, the answer is no.

      You will need to determine what section of the engine is not working correctly through old-school troubleshooting, and buy accordingly to your particular needs of the moment.

      Hope this helps and if you need any particular tools you can visit my shopping mall at under the appropriate category, by scrolling to the right and choosing from the menu category bar.

    • HarperSmith profile image


      9 years ago

      Nice informative hub. Do you know if there any handheld testers for old classic cars. Thanks


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