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AA wots goin on ere then? On Board Diagnostics – OBD

AA vanIOBD system used by the AA had occasion to call the AA this morning. I was out at the crack of before dawn to take in my usual swim on the way to work when knock me down with a thirty pound sledgehammer the car wouldn’t start. Never had a problem before but hey, stuff happens…

I called the AA at 7.40 am and was promised a van in my front drive at 8.40. Ok cool. I had my usual Weetabix with banana and before I knew it an sms came in on my Samsung Galaxy S3 telling me the AA man would arrive at 08.10. Very good. Impressivo.

OBD connectionFollowing breakfast I moved into the front room to keep an eye out for the van and at just before 08.40 it drove past. I must get the house number on the gatepost fixed. Walking out to the drive I saw the van drive past the other way – I definitely must get that number fixed !:)

At the third pass I flagged the van down and it pulled into the drive. Yay.

Fortunately the car didn’t start as soon as the AA man tried it. I had this irrational worry that once he got there there wouldn’t be anythingOBD crypton AA wrong with it. Out came his diagnostic kit and he set to work. Now this is really the point of this post. The AA man plugged a connector into a socket just below the steering column that I didn’t know was there, got his ruggedized tablet out and ran some tests.

Trying the engine again the car started straight away! Blimey!!

The AA man (I should have asked his name – it may be on the docket which is in the car but I can’t be bothered to go out and get it) showed me that there were no error codes and thatOBD toughbook basically there was nothing wrong with the car/engine. He suspects it was a low fuel pressure or at least a temperamental fuel pressure sensor. If the on board computer doesn’t think there is enough fuel pressure it won’t let the car start. The car deciding to start was nothing to do with the plugging in of the OBD kit. It is now ok again.

The worry of course is that this might happen again. I didn’t want to keep thrashing the battery to start the car in case it ran it flat (fwiw) and itwon’t really be any different another time though there is a scenario where if the car isn’t going to start it doesn’t matter what the state of the battery is..

The information obtainable via the OBD interface was impressive. I could in real time see the changes to the fuel pressure as I pressed my foot on the accelerator. I’m sure there must be a market for an application that streams data from the engine management system to a cloud based data base that would allow me to observe the trends related to what is happening with my car engine. It might help me to spot problems before they happen and mean I’m less likely to miss my swim in the morning.

This is a machine to machine big data job with a mobile data SIM connected to the engine management system. It would be very simple to add a tracking function to this as well.

This may be available but I’ve not seen it. Car tracking systems seem to be more about recovering stolen vehicles and spying on your truck drivers to make sure they aren’t slacking than anything related to anticipating problems with the car. In itself this is fine but more could be done.

You could use the same SIM for in car internet browsing whilst on the go. Not for the driver but maybe for the kids use with an iPad to keep them entertained on a journey.

Anyway that’s my threppence halfpennyworth. The car is fine now Praise Be!

Trefor Davies

By Trefor Davies

Liver of life, father of four, CTO of, writer, poet,

12 replies on “AA wots goin on ere then? On Board Diagnostics – OBD”

I bought one of these:

And keep it in the glove box. It means a few things:

1. If the ECU warning light goes on I can find out if it’s safe for me to drive the car
2. I can clear a warning that may be intermittent without paying the garage £60
3. I can tell if it’s something I can fix myself (e.g. rear lambda sensor, which I did fix myself)

All for £ not much – it’s not the AA man’s all singing all dancing thing, but was worth it for me.

And yes, OBD is magic(tm)

It’s worth getting the OBD /OBDII cable or the Bluetooth one

With a VW and the VagCom software you can really play like;
How long should my lights stay on for after I turn the car off
Or Would you like global unlock or just selective

I wouldn’t recommend changing any ECU bits though because you can really break things 🙂

How long will be before the AA have to come out and plug a keyboard in and do CTRL-ALT-Del
Or leave the battery out for 10min

Some cars already update themselves on free WIFI when you stop to fill up
This is good so long as the update doesn’t crash the car…(software)

If you get an Aston Martin top spec they will ring you and warn you of low tyre pressure or book your next service in by tracking the cars data

If you’re into electronics and a bit of DIY, there’s a whole world of OBD and CANBUS out there with Arduinos.

A good starting point would be – one day followed up with a GPS shield and a GPRS shield 🙂

A friend of mine is the brains behind too, which combines all of the above in a data logging capacity. It’s hugely impressive when you see the stats coming out of the systems that we take for granted and drive every day!

If its diesel, be wary of the fuel injectors failing – if they fail the fuel can go via the leak off back to the tank but this causes the drop in the fuel pressure – symptoms typical of what you had. Have you had any other running issues?
You can get cheap OBD code readers for not much money – full telemetry readouts ones are either manufacturer specfic like vagcom and a reasonable price – multi vehicle ones cost £££.

you guys need to join the modern world.

BMW has had a data sim in their cars since 2005. It’s called Connected Drive.

My old 535d that I bought in 2006 would allow you to transfer locations from google maps, upload contacts, manage routes and handle service booking and search google for business locations, you could located your car via an iPhone app- it was excellent.

My M3 has the latest Connected drive – which does all of the above plus:

Has a Twitter and Facebook Client, Web Radio. Will read emails from my iPhone or Blackberry.

It has Internet access and uses your regular phone as a tether.


I can also stream video or music via DLNA to the screen in the car or to the cars audio system.

With the BMW iPhone app, I can blink the links, turn on/off the heating system, track the location of the car, get stats on the cars performance (MPG etc), open the door, lock the car, open the boot, make the windows go down etc.


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