Scan Tool Basics

Listen to a discussion about the Auterra scan tool on the All About Cars radio show with hosts Jon Woods and Tom Yocom.

Visit the following web sites for independent Auterra product reviews. 

What is a scan tool? 

Modern automobiles rely upon computers to control and monitor all aspects of vehicle operation. When most people think of computers, they think of a desktop system such as an Apple Macintosh or an IBM PC-compatible. However, small computer microchips silently perform many mundane tasks without the average person being aware of their existence. Today’s automobile contains numerous on-board computer chips responsible for many systems such as the engine, transmission, and antilock brakes to name a few.

The automobile computer relies upon a variety of sensors to monitor vehicle operation such as speed, engine RPM, coolant temperature, and oxygen sensors. While driving, if the vehicle’s on-board computer system detects a problem the computer reports the error using a Diagnostic Trouble Code. A Diagnostic Trouble Code number indicates the problem with the vehicle. For instance, Diagnostic Trouble Code P0503 means the vehicle speed sensor is intermittently not providing the correct reading. 

The scan tool connects to the vehicle using a standard, easy-to-locate electrical connector. No tools are required to access the connector. Once connected, the scan tool communicates with the vehicle’s computer to obtain diagnostic information, such as a Diagnostic Trouble Code.

If the vehicle computer detects a problem, the driver is informed using the “Check Engine” or "Service Engine Soon" light on the vehicle’s dashboard. This light is also known as the Malfunction Indicator Light (MIL). When this light illuminates, a Diagnostic Trouble Code is saved into the computer memory ready for the Auterra Dyno-Scan to read the value. 

Not all Diagnostic Trouble Codes illuminate the Check Engine light. Sometimes the vehicle needs to see an error a few times to ensure the problem isn’t just a temporary glitch. Other times the computer determines the problem isn’t emission related and the driver is not notified. Therefore, periodic checking of the Diagnostic Trouble Codes helps detect problems early before becoming more costly to repair. For instance, the computer may detect a problem with the automatic transmission but since the failure is not emission related the computer may not illuminate the Check Engine light. The transmission failure may also be difficult for the driver to detect just by driving the vehicle. Only a scan tool can reveal that a problem exists and the cause.

What are some uses for a scan tool?

The scan tool assists the home mechanic in repairing the automobile by providing access to the vehicle sensor readings. The scan tool displays, in real-time, the value measured by any sensor. For instance, if Diagnostic Trouble Code P0503 (vehicle speed sensor intermittent) is logged, a verification of the speed sensor using the scan tool may assist in confirming the failure. Most manufacturer and aftermarket vehicle repair manuals make use of a scan tool to assist in diagnosing and repairing problems. 

Many repair shops charge $100 or more to read the Diagnostic Trouble Code from the vehicle’s memory one time – an expensive and time-consuming operation. Owning your own scan tool enables you to read and clear the Diagnostic Trouble Codes as often as necessary.

Even if you don’t repair the vehicle yourself, knowing the Diagnostic Trouble Code number before taking the vehicle in for repair makes you an informed consumer. If the Diagnostic Trouble Code indicates a faulty vehicle speed sensor, for example, and the mechanic talks about a major engine overhaul, you may want a second opinion before leaving the vehicle for repair. 

Once the vehicle is repaired, the Diagnostic Trouble Code(s) can be erased and the Check Engine light extinguished using the scan tool. In states that require a smog check, an illuminated Check Engine light fails the emission test, even if the repaired vehicle might otherwise pass inspection. The Auterra OBD II Scan Tool extinguishes the Check Engine light. 

Data Logging Features

All Auterra products data log and record vehicle sensor data while driving. The live sensor data is read from the vehicle diagnostic port and saved to a file for later replay or analysis. 

On Palm, the recording may be played back or exported to a PC for future analysis. On Windows, you have two choices of viewing logged data. You can playback the data just as it was recorded, like on the Palm, or you can use the Analyze Live Data screen and view the entire recording all at once. View line graphs in a stacked or side-by-side view. Zoom in/out and scroll each axis independently. A data cursor obtains x-y, period and peak-to-peak values. All recorded data can be exported into a variety of formats. 

Dyno Features

The Auterra scan tool is unique in that its not just a powerful diagnostic tool, its also equipped with a built-in dynamometer used to measure horsepower and torque, acceleration times, such as 0-60 and 1/4 mile, and even fuel mileage. The dyno features operate by measuring speed and RPM from the vehicle's computer as it accelerates through the RPM range. Once the software has collected the data, it displays a graph and numerous statistics based upon the vehicle test run. Extensive testing against the Dynojet chassis dynamometer has shown the Dyno-Scan to be very accurate.

A dynamometer, or dyno for short, is used to measure the power produced by an engine. Up until now, automotive dynos used were either crankshaft dynamometers or chassis dynamometers.

Crankshaft dynos require the motor to be removed from the vehicle. The power is measured directly at the crankshaft, or flywheel, and is not affected by transmission and axle powertrain losses. Vehicle manufacturers spec crankshaft power on new cars and trucks.

Chassis dynos test the entire vehicle. The vehicle is tied down to a large machine and the drive wheels are placed over a rotating drum. The chassis dyno tests the entire powertrain system, not just the crankshaft power. This is a more realistic test since it measures the power delivered to the wheels, not just the crankshaft. As such, the power figures measured are always less than with a crankshaft dyno since the powertrain robs some power from the vehicle.