Davis Instruments has a new datalogger that plugs right into the diagnostics port of most 1996 or later automotive onboard computer. It will log all the information your mechanic can glean from the ODBII, including what just tripped that pesky "CHECK ENGINE" light. Once your data logging session is over (up to 75 hours monitoring), you plug it into the serial port of your PC and get the information nicely formatted in charts and graphs. Product Info Here. Be sure to check out the PDF files for more information.