Most new vehicles these days feature some sort of instant or average fuel economy meter. In many cases, there is also some sort of eco light that illuminates to let drivers know when they're driving efficiently. For older vehicles (and for owners who want more information beyond a simple, "Am I driving efficiently, yes/no?") there are the aftermarket diagnostics devices. These devices plug into the onboard diagnostics port that is present on most vehicles manufactured after 1996.
Of the examples of these devices that we've tested, the Bully Dog WatchDog is one of the best designed. Its control scheme is both easy to understand and to use at an arm's length; its interface is the easiest to read at a glance and use to navigate at highway speeds. But is it worth its $299 price tag? Well, that all depends on you.
The WatchDog is available with a black or white shell, has about the same footprint as a business card (3.5 inches wide by just over 2 inches tall), and is about half an inch thick. The unit features a smallish, 2.25-inch color LCD. The display is not touch-sensitive, but is flanked by seven touch-sensitive pads on either side (five on the left, two on the right) with which the user interacts.
Along the unit's right edge is a Mini-USB port and a microSD card slot. On the unit's back is a slot for the included mounting arm and, oddly, an HDMI port.
The HDMI port isn't used for connecting to your HDTV, however. Instead, the WatchDog uses an included HDMI cable to connect to its OBD-II connection. The connector itself is a 1.75-inch-by-2.25-inch-0.75-inch-thick block of plastic and electronics that connects to the onboard diagnostics port. Along one side is the HDMI connection used by the WatchDog and a connection point for a power wire that must be routed to the vehicle's fuse box. (Our test vehicle, a 2011 Ford Fiesta, did not require this power and was able to draw sufficient power from the OBD-II bus.) Along the other side is a Micro-USB port, a smaller four-pin Micro-USB port for use with an optional auxiliary sensor, and a 2-amp blade-type mini fuse. On top of the connection is an on/off toggle that enables you to connect and disconnect quickly without physically removing the plug.
Of its bulk, about 0.5 inch of the connector's height is the OBD-II plug itself, so the connection isn't as high-profile as it may seem at first. Additionally, most vehicles hide their OBD-II connection in the footwell or beneath the dashboard, so the black plastic wart will at least be out of sight for day-to-day use. However, the HDMI cable itself will not be, and unfortunately such a thick cable makes cable management in the car difficult.
Holding the WatchDog in place during motoring is a flexible windshield mount. This mount connects to the WatchDog using a slotted peg and connects to the windshield using a lever-actuated suction cup. We found that the suction cup wasn't exactly the strongest that we've tested, but the WatchDog itself weighs less than an ounce, so the mount proved sufficient during driving. Between the two mounting points is a flexible neck that can be bent into nearly any shape or angle that the user desires. The entire arm measures 8 inches from end to end, so there's plenty of room for positioning.
Use and performance
Note: Initially, we wanted to test the WatchDog with our normal test vehicle, a 2006 Chevrolet Aveo. However, during setup, we realized that the Aveo lacked the OBD-II protocol needed to communicate accurately with the WatchDog, despite being manufactured a decade after the ports became standard. As a result, we tested the WatchDog with a 2011 Ford Fiesta hatchback. You'll want to make sure that your vehicle is compatible with Bully Dog's diagnostic technology before you make your purchase or throw away your receipt.
After connecting the WatchDog to our test vehicle's OBD-II port and flipping the power switch on (with the engine running), we found that the unit immediately booted to a Setup Wizard. During the course of this Wizard, the unit automatically detected our vehicle's communications protocol and prompted us to input engine displacement, vehicle curb weight, fuel economy goal, and sensitivity of metering. We were also asked if we wanted to use the Driving Coach function. After a confirmation of the input settings, we needed to perform a quick calibration in which the WatchDog asked us to run through a few seconds of full-throttle acceleration; you'll want to do this in an area where it's safe, not your driveway.