Modern Vehicle Computing: On-Board Diagnostics

Prior to the OBD-II standard, vehicle manufacturers used a range of non-standard or proprietary diagnostic systems and standards. Some code scanners worked only with certain vehicle makes, or a universal scanner might be paired with a number of cable/interface adapters in order to communicate with the various vehicle makes. A single OBD-II compatible scanner can work with any OBD-II compliant vehicle to read the standard parameters and clear fault codes.

Prior to the OBD-II standard, vehicle manufacturers used a range of non-standard or propri

OBD-II Drive Cycles

A vehicle with an active fault code will not pass an emissions test. A scanner can be used to clear the code, and if the fault condition is no longer present, the ‘Check Engine Light’ (CEL) or ‘Malfunction Indicator Light’ (MIL) will remain out. Whenever you perform a repair on an OBD-II vehicle, disconnect the battery, or clear the fault codes, the system must run onboard diagnostic tests to determine the state of all the sensors and control modules. Essentially, the system is looking to see a series of actual driving conditions over which to make emissions-related tests.

These drive cycles can vary by manufacturer and model, but can be found online with a little research. Until these drive cycle tests are complete, the ‘readiness monitors’ will not be set and the vehicle cannot be tested for emission compliance. If you’ve done recent work or a code reset, you want to check the monitor status with a scanner to ensure readiness before making a trip to the emissions test station.

One product we tried was the GoPoint Technology GL1 interface. The data cable allows you to connect your Apple iPhone, iPad or iPod Touch to your OBD port. GoPoint includes their GL1 Scan Tool software for use with the interface so you can check trouble codes, clear codes, or monitor OBD engine parameters.

One product we tried was the GoPoint Technology GL1 interface. The data cable allows you t

OBD Monitoring

Now that we know a bit about what’s running around inside an OBD-II system, how can we use that information to our advantage other than troubleshooting a fault we experience? We took a look at several OBD monitoring tools on the market. These are intended to be placed in the vehicle cabin and can be used for real-time monitoring of powertrain conditions. What used to cost thousands of dollars to get detailed access to OBD parameters is now available in several user-friendly and economical formats.

Each of these units is able to read a basic set of real-time OBD parameters, aid in checking and improving fuel mileage via driving habits, read diagnostic trouble (fault) codes, and clear codes in memory. However, each also has some unique abilities and choice of unit can come down to specific needs for the devices.

ScanGauge II from Linear Logic is a compact OBD monitoring unit with an LCD screen capable of displaying four monitored values simultaneously in a digital gauge format. In addition to the real-time gauges, it also has a trip computer to monitor mileage and other trip statistics, so it can aid in determining calibrated fuel economy and help you compare the results between different trips. A digital speedometer function can be calibrated to adjust for a change in tire size or gearing.

As with other monitor tools, the ScanGauge II can read diagnostic trouble codes and clear the codes in memory to turn off the MIL. It can also indicate if the readiness monitors are complete in order to make a valid emissions test. For those wanting to dig much deeper into available OBD parameters on their vehicle, ScanGauge II now offers an included feature named XGauge which allows access to the enhanced OBD parameters beyond the basic diagnostics. Linear Logic has a substantial list of enhanced data types on their website and is constantly adding new ones.

With the GoPoint cable connected to our OBD port and to our Apple iPod Touch we had the ability to monitor a good number of engine parameters. Then we tried a $49 program called Dash Command from Palmer Performance Engineering (available from the iTunes App Store). It comes with five dashboards already programmed with virtual gauges, but you can download their DashXL™ dashboard editor that allows you to fully customize your own dashboard design on your home computer.

The graphical interface can monitor fuel economy, log OBD parameter readings, provide a detailed trip computer, and serve as a diagnostic tool for troubleshooting. Dash Command also uses the GPS (iPhone/iPad) and the accelerometer on the host devices to provide real-time race track satellite imagery, an inclinometer showing pitch and roll, plus a skid pad display that can show acceleration & deceleration forces of your vehicle.

Bully Dog offers their Watchdog unit that serves as both as an economy monitor and a performance gauge instrument. In the mode shown here, it can display four monitor parameters on the left and show an enlarged gauge of one of the parameters as well.

The gauges can display up to 15 different parameters (depending on vehicle), has the ability to set temperature and pressure warnings, and can read and erase diagnostic trouble codes.

An interesting feature is the onboard driving coach. In addition to displaying current and trip fuel mileage, the unit can provide visual and audible indicators to show how efficient you are driving. You program all your specific vehicle details so the coach and other features are matched to your engine displacement, vehicle weight, etc. so you can quickly learn what driving behaviors can save you gas money. For lead foot testing, you can also log and store ¼ mile times and similar performance statistics.