Using an OBDII Code Reader with an Aston Martin DB9

Using an OBDII Code Reader with an Aston Martin DB9If you are interested in doing 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).

Aston Martin Check Engine Light
Dreaded Check Engine Light (CEL)

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

Aston Martin AMDS Linked to my DB9
My DB9 linked up to the AMDS computer at the dealer.

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.  [Update Dec 2019 – I’ve managed to purchase a used AMDS and am starting to learn how to use it.  I’ll post something about this in a future article]

Manufacturers and OBDII Standards

OBDII LogoMost 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 openly published their custom codes, so most aftermarket readers can only speak basic OBDII to our cars, and a LOT of the information is unavailable to them.  Why?  Perhaps Aston Martin was trying to keep it so that only the dealers using AMDS can access it, forcing us into the dealership. [Updated] There is some good news here, several aftermarket devices can now speak Aston Martin (see below).

Aftermarket OBDII Code Readers

Autel MaxiDiag Elite MD802
Autel MaxiDiag Elite MD802

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.

[Updated Dec 17, 2017]

The Autel MaxiDiag Elite MD802 is being replaced with the Autel MaxiDiag MD808 Pro.   Available for about $279 USD on, the MD808 is the newer/better model.  A significant upgrade is that it now includes a lifetime of free updates so it will always have the latest codes for the newest models.  As far as I am aware it still DOES NOT support Aston Martin models directly.   But we have a better option to choose from now.

Foxwell NT510 OBDII Reader

The Foxwell NT510 is a new OBDII reader that is very similar to the Autel, but INCLUDES Aston Martin specific codes and can even reset the Service Required light.   It also includes lifetime free updates and is available for just $149!  This is now my recommendation for an OBDII reader for your Aston Martin and you can read my full review of the Foxwell NT510 here.

Where to Hookup Your Code Reader

Aston Martin DB9 OBDII Connectors
OBDII Connectors

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 for talking to the engine.
  • The connector labelled BODY is for talking to the body system network, things like the Seat Modules, Window Modules, Stereo system, etc. and will only work with an OBDII Code reader that knows how to speak Aston Martin (like the Foxwell mentioned above).  If you link up with a generic OBDII tool 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.

BODY OBDII socket protective cover in place on Aston Martin DB9
BODY OBDII socket cover

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

Establishing OBDII Communications to an Aston Martin DB9
Establishing Communication
OBDII Code Reader Information connected to Aston Martin DB9
Current ODBII Data

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.

If you are using a Generic OBDII tool like the Autel, here are some othe articles that show you how to access the data:

Check out my OBDII Collections Page (here) to see all the OBDII related articles I have posted.

17 thoughts on “Using an OBDII Code Reader with an Aston Martin DB9

    1. P Codes article is coming along, but the next one soon to be released (insider preview) is actually a trick I just learned. Rather than using OBDII on the Scanner, use Scan, Select Ford of Europe, Manually select the engine, and select a 3.0l V6 from the MY2005. You’ll get a ton of usable information. The Tire Pressure Monitoring system isn’t part of it, I believe the TPMS has its own reader, and even separate connection in the trunk. Stay tuned for the full article on the Ford method.


      1. Joel

        Hi Steve,

        Let me start off by thanking you for your efforts in advancing knowledge for us DIY-ers. It must take a great deal of time to shoot, edit and write these posts, and I thank you for it.

        I recently purchased a DB9 (2009MY) with about 50,000 mi (81,000 km) on her from a local AM dealer. The vehicle had two previous owners. At the time of my test drive mid-August everything seemed generally fine with the vehicle. Or at least I thought so. Most importantly, there was no MIL/Check Engine light on. I purchased the vehicle about a week later, and because I was about to take an extended vacation, did not take delivery until last week (Sep. 22).

        When I picked up the car, I noticed the MIL was on and displaying the ’emissions service’ message. I asked the salesperson about this and he said not to worry about it and that it will disappear, claiming gas cap issues. Subsequently I did some reading, learning about gas cap issues, etc. I checked the cap and it is white, and fully closed. I also discovered your blog, read all your posts, and last night purchased the same OBD-II reader you have (Autel MaxiDiag MD802). While I haven’t had a lot of time to review data, I did learn that there are significant misfires on cylinders 5, 6, 10, 11 & 12. I also have some PATS codes, but not sure about them. A snippet of my data is below. I have the following questions:

        1. The data I have shows DTC’s were cleared just prior to my test drive. How could the test drive not have the MIL showing given the extent of misfires being generated?

        2. My understanding of cylinder numbering is that left bank is numbered 1 to 6 (front to back) and right bank is 7 to 12 (front to back). Is this correct? If so, my cylinder misfires are at rear of engine on both left and right sides. My understanding is that this does not seem likely point to a vacuum issue as these are usually isolated to left or right banks, but I’m not sure about that. Any comments?

        3. I understand that when things get really bad, cylinders get shut down, but not sure if damage to catalytic converters can still occur given the extent of my misfires. How risky do you think driving the car is in this condition?

        4. Do you know what the $80 to $84 Mis-fire Monitor Tests are? (See Mis-Fire Monitor Data below).

        5. The quantity of mis-fires on my cylinders seems high to me, but not sure if that’s true (having no prior experience with these matters). How severe is this?

        Thanks for your time Steve.



        Trouble Codes
        P0300 $07EE
        Random/Multiple Cylinder Misfire Detected
        P0311 $07EE
        Cylinder 11 Misfire Detected
        P0316 $07EE
        Engine Misfire Detected on Startup (First 1000 Revolutions)


        Mis-Fire Monitor Data
        $80 Test Status: OK
        $81 Test Status: Fail
        $82 Test Status: Fail
        $83 Test Status: Fail
        $84 Test Status: Fail

        Mis-Fire Cylinder 5 Data
        EWMA Misfire Count 44
        Misfire counts Last 262

        Mis-Fire Cylinder 6 Data
        EWMA Misfire Count 10
        Misfire counts Last 100

        Mis-Fire Cylinder 10 Data
        EWMA Misfire Count 66
        Misfire counts Last 114

        Mis-Fire Cylinder 11 Data
        EWMA Misfire Count 487
        Misfire counts Last 994

        Mis-Fire Cylinder 12 Data
        EWMA Misfire Count 100
        Misfire counts Last 198


        Fault Codes(3)
        B1600-FF CMDTCs
        PATS Ignition Key Transponder Signal is not received.
        B1601-FF CMDTCs
        PATS(Passive Anti Theft System) received incorrect key-code from ignition transponder.
        P2800-FF CMDTCs
        Transmission Range Sensor B Circuit (PRNDL(Selector lever position (PRND321)) Input)


      2. Hi Joel. Thanks for taking the time to write, and I appreciate the Kudos. Sound to me like they might have reset the MIL just before your drive as you suspect.

        I am no AM mechanic, but I’d say you have a couple of separate issues going on. The Misfire issue seems to be the biggest at the moment. Member the misfire count resets each time you drive it, so those are significant numbers. I think the shutdown percentage is at 1.5% or so. P311 and P316 are those cylinders having serious issues.

        The PATS issues might be separate.

        THis is going to sound stupid, but I’ve never been sure on the cylinder numbering schema. Something I need to nail down, but I can’t even find it in the manual. If you find a solid online reference, please let me know.

        The S tests its referring to I don’t know what those are either (yet).

        I guess if you have any leverage with the dealer, take it back with this data and tell them you want a refund unless they address coil pack issue by replacing all 12 packs, plugs and bits. No selective replacements. Ditto for the other P Codes. If you are stuck and they won’t do the work, I think I’d start with doing all the coils and plugs and PCV stuff first, then clear all the codes entirely using your reader, then see how it settles out afterwards.

        Would I drive it in this state? Not really. Moving around in the driveway, or maybe back to the dealer, but I wouldn’t do any regular driving.

        Let me know how it turns out.


  1. Pingback: Restarting your Engine for the First Time after Changing the Spark Plugs and Coil Packs in an Aston Martin DB9 – Aston 1936

  2. Scott

    Just bought an autel md802 maxidiag elite, can’t get it to communicate to 2005 db9. Connected to a Lexus, f350, ram 3500, 2 different f150. Firmware v2.02 , software v5.06 , hardware v1.00
    Any ideas? Tried both ways you did, in your videos .


    1. Hi Scott. Not sure what to add, but I’d try two things (that you probably already have).

      First, be sure you are NOT on the Body OBDII port. The Autel will not figure out how to communicate.

      Second: While connected to the proper port, use just the basic generic OBDII function of the Autel. You should see it initially trying to link up using an array of protocols before its finally online. If it comes online, great, then you know the communications layer is working properly. If it can’t communicate, something odd is happening and it may be a problem with your car unfortunately.

      If this does work, then I would back out of the generic OBDII menus, and then try accessing the car as a Ford, 2005, 3.0l V6 as I do in the article and video.

      Let me know how it goes.


  3. I have the Foxwell NT520, and this reader allows you to save live data. Just go to live data, select all or specific modules, and press save. Then drive, or do whatever you need to test, and after that press “stop save”.
    The reader saves the data in the Folder Aston\savefile\x.cbf of the memory card in the Foxwell

    So if you want to extract the stored live data of your run, insert the memory card in your reader, then access it from your Windows Explorer and go to the folder. Upload the respective file to: and then download the .csv file which you can open with Excel.
    The guy mentions, there is no timestamp in the cbf file, so if you want to trigger some timestamp while testing something, press one of the cruise control buttons (enable disable), this will show up as distinctive event in the excel so you can mark some testing or so.


  4. Jerry Janowitz

    Hi Steve,

    I bought a Foxwell NT510 OBDII Reader based on what I read here, I cannot seem to find the area that shows the cylinder mis-fire counts when I had it connected to my car. Can you share how I may locate it? I am getting ready to replace my plugs and coils following your excellent videos, thank you for those!! The dealer wants $4,400 to do the job on my 2009.



    1. Hi Jerry. To monitor the misfires you actually don’t use the section of the special codes unique to Aston, but rather the generic OBDII functions of your Foxwell. I should put out a video on this. You can see almost how to access it at the 24 sec mark of this video Rather than selecting Live Data, Select On Board Monitor Test. Its only on one of the PCMs, I can’t remember if its the Primary or Secondary. But, when you get in there it will say Misfire Monitor Cylinder 1, etc. Hope this helps a bit.


      1. Jerry Janowitz

        Thanks Steve! I found the cylinder data via the on board monitor test like you suggested, for some reason all of the counts are zero yet I can feel the mis-fires happening. I will try again when I have some time.


      2. Good that you found them. One requirement for them to be working I believe is that your ‘Misfire Correction Factors’ have to be in a ‘learnt’ state. If these aren’t learned, then it can’t compute the misfires. I have another article on how to learn these, which I think includes a note on how to use the OBDII to see if the car knows them already (come variable like 36_1 or something, can’t remember without re-reading the article). If they are not learned, you’ll need to follow the blog article and go out and do a drive to learn them. Good luck.


  5. Jerry Janowitz

    I just watched a video from Mike at Bamford Rose on this topic and I found my issue.
    My car had a new battery installed very recently and I noticed on my Foxwell that the misfire detection was not enabled, I suspect due to a battery disconnect. Thus the misfire system was not on and viola no data on my cylinders. Mike describes how to test for a misfire while driving and I have confirmed I really do have the issue, I suspect cyl 8 and 12, but I will be replacing all coils and plugs. Very helpful information between you Steve and Mike! As soon as I get my parts from Aston Martin Bits, I will start the repair using your videos.


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