If you are brave (or dumb) enough to do some of your own maintenance on your Aston Martin DB9 one great tool to have in your repertoire is an OBDII code reader. OBDII stands for On Board Diagnostics version II – an industry standard communication method that modern cars with computers use. By linking up your OBDII reader to the car, you can ‘talk’ to it, learning some real-time information from the cars Powertrain Control Modules (PCMs).
Of particular use is to understand what’s going on if the dreaded Check Engine Light (CEL) comes on. This is also sometimes known as the Malfunction Indicator Light (MIL) or Idiot light. Without a code reader you are completely in the dark as what might have tripped the CEL, and at the mercy of a Dealer to find out what’s going on. With a code reader, you can link up to the car and it will tell you a much more specific error code (a P code in Aston Martin speak). This will narrow down your troubleshooting greatly, and often it can be a simpler DIY issue to address and then clear the error code and reset the CEL.
Aston Martin’s Official System
When you go to an official Aston Martin dealership, they don’t use some generic OBDII tool, they have a very fancy (and expensive) Aston Martin Dealer System (AMDS) computer that links up to both the powertrain and body system networks in the car. The AMDS is much more than a simple code reader, it can talk to all aspects of the cars electronic systems, update/flash the software in the computers, reset settings, all sorts of great stuff. I thought ‘Cool’ – I will just get one of those. I searched eBay and the Internet, and was able to find one for $14,000 USD. Sorry, too pricey for me.
Manufacturers and OBDII Standards
Most any modern car now has computers that run all aspects of it. The network of sensors and computers in the car is loosely call the Car Area Network (CAN). Manufacturers generally conform to the universal OBDII standards, but most also have a set of ‘custom’ codes that are unique to their brands (proprietary). This is reasonable, car design is often very custom. So VW may have custom codes for its Airbag system, and Bugatti might have custom codes for its engine system. Most manufacturers openly publish these custom codes, and fancier aftermarket OBDII readers do more than just the OBDII standard language, they will also know the custom codes for Ford, VW, and even Bugatti. The problem here is that Aston Martin has NOT published their custom codes, so aftermarket readers can only speak basic OBDII to our cars, and a LOT of the information is unavailable to us, and only the dealers using AMDS can access it. Deliberate by Aston Martin I think to force us back to the dealership – bummer.
Aftermarket OBDII Code Readers
I then started to research aftermarket units. There are literally hundreds of OBDII code readers on the market starting at less than $100 for a cheapy unit from the local parts store. I was looking for more than a basic unit, I wanted one that had a bright, large color screen (my eyes are getting older), and that knew as many manufacturers custom codes as possible. Even though this wouldn’t matter much for my Aston Martin, I wanted to use the reader on my other family members cars as well (BMW Mini, Acura, VW). My search lead me to the Autel MaxiDiag Elite MD802. Autel makes many different models. This is a fairly full featured unit, well reviewed, and even can be ‘software updated’ to learn new codes as each new model year comes along. Comes in a nice case, very professional unit. I found it for about $220 on Amazon.
Where to Hookup Your Code Reader
Once you have your OBDII reader, you need to know how to hook it up to the car. This is very simple. In the drivers side footwell if you crawl down and look under the dash near the center tunnel you will find TWO (2) ODBII style connectors. You should see a label on the lower trim piece as well.
- The connector labelled OBD is for the OBDII code reader. This is the one we want to use.
- The connector labelled BODY is for talking to the body system network, things like the Seat Modules, Window Modules, Stereo system, etc. and is NOT to be used with an OBDII Code reader. If you link up in error to this connector, your reader will likely not be able to establish communication.
There is a difference between Left Hand Drive (LHD) and Right Hand Drive (RDH) cars. The OBD connector is always the one towards the drivers door, the Body connector is always closest to the center tunnel.
The fact that there are two connectors obviously was causing some confusion. Aston Martin issued Field Service Action 144 (FSA-144) in June 2006 instructing the North American market dealers to install a protective cover/boot overtop the BODY OBDII connector to minimize the chance of an incorrect connection. You can read the entire FSA-144 here. My car was built before this FSA was released, and my Damn Previous Owner (DPO) or his dealer didn’t get this done while under warranty, so my car hasn’t had this modification performed.
Using Your Code Reader
So, now crawl into the footwell, find the OBDII socket, and connect your code reader. My code reader gets its power directly from the car, so it powers up immediately. Even with the car off, the unit will power up. But, I have learned for communications to work, the ignition key will need to be in Position 2. The car doesn’t need to be running (it can be though). I then need to tell my reader to ‘connect’ to the car and establish communications to the CAN network. This just takes a few seconds and then Ta-Da! You’re talking to the car and now can view P codes, live engine data and more.
Check out this short video of me showing where the connector is and linking up.
I also have a post about how to get many more (200+) live powertrain parameters by asking your OBDII reader to talk to the PCM using Ford factory proprietary codes.