OBD II Diagnostic Tools

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.

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.

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.