Reading Codes OBD - with what?

Anyone want to offer any opinions on the OBD (which I am assuming stands for On Board Diagnostics?) readers out there? The ones at www.autoxray.com look a bit pricey and perhaps a bit more then
your "moderately experienced" DIY may use. On the other hand, the ones at http://www.carchip.com/ seem affordable but are they too little (not size, features). Where would one find a Key for the codes? (this code means . . .)
Your thoughts are much appreciated. Ken
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The higher-priced units might appear to do more than the basic ones, but in fact (after having gone through this recently), they won't do anything but the basic functions on Mercedes-Benzes. You need the professional hand-held testing kits (diagnostic laptop computer with special software, or a Palm Pilot with MB diagnostic module) to access MB's enhanced systems ($3K); the dealer's Mercedes Star Diagnostic system is $25K+ and uses its own diagnostic connector on the car.
Any OBDII reader will give you the basic codes (it's a federal compliance requirement), so just find the easiest one to read. On my late-model MBs, the access port is just under the hood release latch handle (in the driver's footwell), under a thin plastic cover that swings open. If you go shopping, look for any unit that reads Generic OBDII. That'll do it.
Our local Schucks, Krager, Checker auto stores (Western USA) now have free AutoXRay loaners (with deposit) to allow customers to take home for retrieving OBDII codes. They give you three days with the unit, and the test takes about 10 minutes to do once connected to the car. I purchased an AutoXRay unit, used it for basic OBDII and returned it when I found out it wouldn't do enhanced MB functions, even with an expensive softare upgrade. But for basic codes, the loaner unit was fine.
Here's a list of OBDII codes: http://www.obdii.com/codes.html

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If you have a laptop, you can purchase hardware from the following site for $88 including shipping:
http://obddiagnostics.com/index.html
The software which works with the hardware can be downloaded from the same site and is available in Windows, DOS and Linux versions.
I've used the DOS and Windows versions and am quite happy with the product. It permitted me to diagnose a defective air mass meter and thereby correct a check engine light problem. Since I am a do-it-yourselfer, I have no knowledge as to what the more expensive scanners offer, but this arrangement offers more than just a reading of the OBDII codes. For example, it reads the air mass meter output and plots the voltage on the O1 and O2 sensors. You can download the software and operate it in the simulated mode to see what it offers.
The Linux version is even said to have the source C code available, but I have no experience with its use.
Dan

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