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Once the Federal government mandated standards for auto fault codes, a number of code readers appeared on the market. The simplest of these simply tell you what fault codes have been registered; the most complex let you change parameters of your engine computer (where possible), and see in real-time what the various sensors are showing. One enterprising company set up a small, innocuous recorder that, in addition to reading and storing fault codes, took a reading every few seconds of sensor outputs, and also recorded panic stops and fast acceleration, so parents could monitor their teenagers' driving without their knowledge.
For serious troubleshooting, though, an almost-constant capture of sensor readings is more important than every-few-seconds. Automakers themselves use a special system where pressing a button records sensor readings pre-and-post button-press for later study. Dealers have special autopilots that are loaned out to people with troubling sporadic issues. AutoTap is similar - it connects in to the auto computer system, reads fault codes, and can record sensor readings as requested.
One of the problems of recording sensor data is where to store it. AutoTap solves this by using either a computer (Windows only, though we suspect a MacBook with Parallels Workstation would be able to run it) or a Palm Pilot to record the data. The software running on the laptop or Palm also provides a user interface. The device itself is a big blocky thing that plugs into the standard computer interface present on every car, usually right under the dashboard. On some cars you can easily drive with the AutoTap plugged in; on other cars, the device gets in the way of the clutch. For most people, this probably isn't an issue. The AutoTap is USB powered, so it has a single extra-long cable that runs to the computer. That cable is long enough to be routed the long way around so it doesn't get in the way. It works on any OBDII compatible vehicle, including CAN models (newer Chryslers and others), which covers quite a range of models and years.
When the AutoTap is connected from a laptop, there is a choice of two programs to run. AutoTap Reader is a simple and fairly quick code reader, which reads any fault codes, tells what they mean (in rather technical terms), and allows the owner to shut off the Check Engine light easily. Keep in mind, though, that like most devices of its type - the under-$10,000 variety - the AutoTap often fails to see manufacturer-specific codes. Thus, it can read the industry standard P0700 "there's something wrong with my transmission electronics" code, but not the more specific code that would tell you to replace the output sensor. (A list of the non-generic, Chrysler-specific signals it can read is at this link).
The main AutoTap program, though, allows the owner to see the output of a wide variety of sensors, and to change the operating parameters of Corvettes. The range of sensors it can read depends on the model and year of the car; when first connected, it tries to find the VIN of the car, and gives the owner a shot at typing it in if it can't find one. Based on the VIN, it knows what to look for and can find some (but not all) "non-generic" information; it then takes about 10-20 minutes searching and finding data sources, based on our experience using an old 550-MHz Sony Vaio running Windows ME (you can save the car's profile and save time on the next hookup). Then the screen lights up with a large table and two big gauges; navigating through an unnecessarily unintuitive user interface, you can change the contents of the table and the gauges. The screen reflects the actual car conditions with a fairly small lag time, so hitting the gas causes the engine load dial to flit upwards a moment later. Recording and playing back data is easily: a press of the spacebar starts recording (and shows a big red bar on the screen), and another press stops recording. The operator is prompted to save the data capture, and can then play it back on the screen for diagnosis. Alternatively, you can save the results as a CSV file, which can be opened by Excel or OpenOffice, and read them in table format.
The format of an output table is interesting, and reinforces the idea that you should really only track what you're interested in; the system can only record every so often (40 times a second at maximum speed), and on our 300M, it took about two seconds to run through all the sensor readings and record them, so that we had an every-two-second snapshot. If we had recorded just the one item we were interested in (which unfortunately wasn't available! that is, gas tank reading), we would have had a nearly continuous graph, which can be very useful.
We did not test the Palm Pilot version; while obviously much more portable (and cheaper if the recording device breaks), the small screen would probably get in the way. The version we did test - AutoTap Diagnostic 2 for Windows - costs about $200, well worth the price premium over the simple code-reader version (AutoTap Reader).
There is no Mac version, but Apple only makes Intel-based machines which can run Windows software using Parallels Workstation or VMWare Fusion; Raleigh Buckner told us that AutoTap worked fine on his Macbook with Parallels.
The AutoTap system is an excellent choice for relatively casual use; it is priced closely to less capable systems, but the large adapter can be awkward if you try to run the system while driving (in data capture mode, or with a passenger operating the computer), and the bootup speed can try the patience of those who are in the midst of troubleshooting. On the whole, the AutoTap can be an invaluable tool for computer-controlled engines.
See our review of a competitor, Palmer's PCMScan.
Those looking for a simpler device in the under-$100 range, which doesn't require a computer in the car, may be interested in CarMD.
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