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OBD II Diagnostic Tools

Posted in How To: Electrical on December 1, 2008
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Even the most inexperienced person can use the compact CarMD OBD-II diagnostic tool. Plug it in, wait till it beeps, unplug it, read the results or download them to a PC for a full report.

OK, so imagine, you're four-wheelin' with a bunch of friends in Baja, or maybe you're halfway into some backroad in Canada. After a beautiful camp, 50 miles from the nearest light bulb, you pack up and turn the key. The "Check Engine" light comes on, and your normally smooth-running engine feels like it is only firing on three cylinders instead of the six it came with. Your buddies know more about fishing than they do about the black boxes that are the heart of your ride. Sure, you carry a war chest of repair parts, but what needs fixing? In this case your "wrench" should be a modern OBD-II diagnostic tool.

One of the most exciting improvements to all vehicles built after 1996 has been the addition of an on-board diagnostic (OBD) computer. For those of us who have added power-enhancing aftermarket chips, we know very well that practically everything that's going on under the hood is monitored, controlled, and stored in a black box, otherwise known as the Power Control Module (PCM). The OBD-II diagnostic tool gives us access to that information with varying degrees of complexity, depending on the model we are using. (There was an earlier OBD-I designed to monitor manufacturer-specific systems on vehicles built from 1981 to 1995, but each vehicle manufacturer used a different diagnostic tool, so each vehicle make required a different code reader or scanner; OBD-II was standardized and made universal and mandatory for '96-and-later vehicles. All vehicles made since then must, by law, test the same systems in the same way. All connectors were standardized with a common 16-pin plug.)

The OBD is so sophisticated, it can detect failures in a wide range of systems. For all OBD-II-equipped vehicles, if a serious problem is found, the computer turns on the "Check Engine" light to warn the driver, and it sets a Diagnostic Trouble Code (DTC) to identify where the problem occurred. Professional mechanics use complicated diagnostic tools costing thousands of dollars. We wondered if there was a more affordable way for the average do-it-yourselfer to take advantage of this technology? Even the most affordable OBD diagnostic tool can retrieve these DTCs.

What You Need
We contacted the folks at Equus Products. They have been designing and manufacturing affordable automotive test equipment since 1982. For Equus, it was a natural progression that has made them a leader in the development of OBD diagnostic tools. When they introduced the Innova 3100 OBD-II diagnostic tool, the automotive do-it-yourself industry applauded its ease of use and its affordable price. To date, more than 400,000 Innova 3100s have been sold.

The easy-to-read screen on the CarMD provides a wealth of information about your engine's condition, and even more can be retrieved from the CarMD website.

Equus was kind enough to loan us an Innova 3100 and a smaller CarMD unit for hands-on testing. They are both plug-and-play tools. Yes, they download all codes for "Check Engine," but there's much more. The unique, patented all-in-one screen display on the 3100 and three-color LEDs on both units show emissions test readiness status. The 3100 can retrieve OBD-II DTCs, Generic Codes (PO, P2, P3, and UO), and Manufacturer Specific Codes (P1, P3, and U1). They automatically update data every 30 seconds when connected to the vehicle, with a memory feature that stores codes for off-vehicle review.

This last feature is interesting. By installing the CD that comes with the CarMD on your PC (sorry, it does not work on a Mac), and registering, you can autolink your tester with the supplied USB cable and log on to the CarMD website to view your complete diagnostic report. You can also call the CarMD toll-free number and speak to an ASE-certified Technician and get help and the information over the phone.

With the Innova 3100 or any of the Innova line, you can use the OBD-II TekLink Software to generate, print, and save detailed diagnostic reports and update the tool via the Internet. By entering the trouble code you've downloaded, you can retrieve a report of the probable cause, suggested repair, and estimated cost of the repair.

What It Tells You
The codes themselves are not difficult to interpret. Each relates to a specific system, which refers to procedures and diagnostic strategies called "Monitors." Currently there are a maximum of 11 Monitors used in OBD-II systems. Monitor operation is either "Continuous" or "Non-Continuous." Continuous Monitors include CC (Comprehensive Component Monitor or CCM), M (Misfire Monitor), and F (Fuel System Monitor). Each vehicle may have a different combination of monitors. An OBD-II diagnostic tool like the Innova or CarMD will only show the monitors supported by the vehicle being tested.

The Innova 3100 diagnostic tool is easy to use, full of features, and affordable. More than 400,000 have been sold.

Non-Continuous Monitors include O (Oxygen Sensor Monitor), OH (Oxygen Sensor Heater Monitor), C (Catalyst Monitor), HC (Heated Catalyst Monitor), E (EGR System Monitor), EV (EVAP System Monitor), 2A (Secondary Air System Monitor), and AC (Air Conditioning Monitor). The easy-to-read owner's manual that comes with an Innova 3100 gives detailed descriptions of each of these monitoring systems.

For example, the CC (Comprehensive Component Monitor or CCM) continuously checks all inputs and outputs from sensors, actuators, switches, and other devices that provide a signal to the computer. The Monitor checks for shorts, opens, out-of-range value, function, and "rationality." Each input signal is compared against all other inputs and against information in the computer's memory to see if it makes sense under the current operating conditions. If, for example, the signal from the throttle position sensor indicates the vehicle is in a wide-open throttle condition, but the vehicle is really at idle, and the idle condition is confirmed by the signals from all other sensors, based on that input data, the computer determines that the signal from the throttle position sensor is not rational (does not make sense when compared to other inputs). In this case, the signal would fail the rationality test.

Looking at the screen of the Innova 3100, all the information is clearly displayed within about 15 seconds of plugging in the 16-pin data link connector or DLC. This unit is located in different places for different vehicles, but most are located just under the dash near the transmission hump.

How To Read It

The easy-to-read backlit screen on the Innova 3100 displays a wealth of information, including Diagnostic Trouble Codes, emissions test readiness status, and much more.

As an example, we might see the "Diagnostic Trouble Code" or DTC PO141, 02 Heater Circuit, Bank 1 Sensor 2.

Each DTC is made up of five characters. The first character identifies the main system where the fault occurs; B (Body), C (Chassis), P (Powertrain), or U (Network). The second character identifies the type of code; O (or sometimes G), Generic, 1 (or sometimes M), Manufacture Specific, or 2, which includes Generic and Manufacture Specific Codes. The third character identifies the specific system where the problem occurred. The fourth and fifth characters identify the section of the system that is malfunctioning. In the example above, PO141, we have a Generic Heated Oxygen Sensor Code.

There are several informative icons on the screen that provide information. For example, when the MIL icon is on, it confirms that the "Check Engine" light was commanded ON. The "Pending" icon illuminates when one or more diagnostic checks have failed, but were not critical enough to turn on the "Check Engine" light. An example of these might be a loose fuel filler cap, or even a door that did not respond to the remote locking button.

The Innova 3100 diagnostic tool is easy to use, full of features, and affordable. More than 400,000 have been sold.

A useful feature on both the Innova 3100 and the CarMD are the green, yellow, and red LED lights that help make it easy to determine the health of the vehicle. You can use this as part of your normal maintenance service, or perhaps before a long trip. It's also useful to determine if a vehicle is ready for an Emissions Test. A green light means that all engine systems are operating normally, all OBD-II monitors have run, and no DTCs are pending or present. A yellow light indicates that a "Pending Code" is present, or that not all of the diagnostic tests have been completed. A red light warns that there is a problem with one or more of the vehicle's systems, and that a trouble code is present which needs further diagnosis. Buying a used vehicle? Carry one of these in your pocket.

Other features include an erase button to clear codes, turn off the check engine light, and reset all monitor status tests. There is also an "auto relink" program that automatically requests information from the vehicle every 30 seconds, to get the latest information while the vehicle is in operation. This allows you to perform a drive cycle to verify that any repairs were done correctly.

Perhaps the most impressive service provided by Innova is the new MyRepairSolutions portal on the website. This VIN-specific, Internet-database repair solutions portal is expected to revolutionize the way do-it-yourselfers and consumers approach automotive repairs. The CanOBD2 website and RepairSolutions database have been under development for more than a decade, and mark a major milestone for Innova and the industry. Through this database, you can get a complete repair solution, including how to fix the problem.

The Innova comes with a detailed instruction book, software CDs, and all necessary cords.

Anyone can register for free to become a member, where they gain access to interactive content, including the most comprehensive and accurate fixes to diagnostic codes anywhere on the web. This extensive database, until now only available to professional technicians, will allow DIYers to pinpoint why their "Check Engine" light is on; get a better understanding of why the failure occurred; print a free basic report with trouble code definitions, monitor status and freeze frame data; generate a vehicle profile to keep track of vehicle history and complete preliminary diagnosis worksheets; access a full library of diagnostic trouble codes and tech tips; and get ready for a state vehicle emissions "smog" test.

The website also features technical service bulletins (TSBs), vehicle recall information, and support from ASE-certified technicians. More importantly, RepairSoutions offers users the opportunity to purchase a comprehensive Advanced Report. This report, which costs less than $10, even provides estimates on parts needed for the repair, labor time required, plus TSBs, recall information, and "how to" info.

Summing Up

The OBD-II diagnostic tool was standardized and made universal and mandatory for '96-and-later vehicles. All vehicles made since then must, by law, test the same systems in the same way. All connectors were standardized with a common 16-pin plug.

OK, so here we are back in camp. Instead of pulling your hair out while your friends are pulling in fish, you plug in your OBD-II diagnostic tool and push a couple of buttons. If you have a scanner, the screen tells you that the left bank of cylinders has a problem. (Option two is to call the CarMD toll-free number on your cell or satellite phone and speak to one of the ASE techs who can walk you through the problem.)

Turns out, the rough washboard roads have caused the wiring harness to come loose. You pull out your toolbox, loosen a few clips, push the harness firmly back into its place, reassemble everything, and delete the "Check Engine" light. Bingo. The engine purrs like a contented cat. Someone just made a fresh pot of coffee. Life is good again.

We can curse all these complicated black boxes. Back in the old days of four-wheeling (not that long ago), we used to say we could gap the points with a matchbook, tweak the timing by ear, and adjust the carburetor with a dime. Then along came HEI ignition, fuel injection, and electronic fuel-monitoring systems. No more points. No need to fiddle with the timing or fuel delivery at high altitudes. No more fiddling with the floats on your four-barrel Holley.

Perhaps with modern engines we have a new set of problems, but at least we now have OBD-II diagnostic tools. Don't leave home without one.

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