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By: Steve Adams. G0KVZ
As presented to the Vange Amateur Radio Society 12th May 2011

Introduction & History.
For many years it has been common for car owners to perform routine maintenance on their vehicles as part of their weekend washing and polishing rituals.
Typical adjustments might have included the clearance of contact breaker points, ignition timing or even idle speed or fuel mixtures.
However, on modern vehicles such maintenance has become generally unnecessary due to vehicle manufacturers incorporating sophisticated engine management systems, and should a weekend mechanic now open the bonnet, there is little that he will recognise.

One of the first engine management systems was the device that was developed by the German Aircraft/Automobile manufacturers BMW, and was used in their BMW 801 14-cylinder aviation engine aircraft engines. In production motor cars, such devices have been seen in cars since around 1980 with the introduction of Hybrid digital/analog devices. These early systems were quite inflexible with their capability of coping with differing conditions. On such early designs, if an error condition was detected, it was possible to initiate a diagnostic routine that would flash a lamp in groups to indicate a fault code. Once the code was determined, then this could be read off a chart to determine the nature of the error. Most modern vehicles use a standard that requires an adaptor to enable the output of the ECU to be interfaced with a computer to enable the output to be interpreted. These modern types also enable the software to display a multitude of metrics, such as coolant temperature, alternator voltage, engine- speed etc.

My story.
Around a month or so ago, the engine fault lamp lit on my car, usually this would result in a visit to a ford dealership, and a bill of over £40 just to determine what the fault was, but o this occasion, I performed a quick sarch on the internet, and found a trader who would supply an appropriate interface lead with suitable software for less than £20. Four days later, this super little device was plugged into a USB port on my old DELL laptop.
Once I had identified the best software from the assortment that was supplied, I soon had the connector identified on the car, and the computer was then connected.
On this occasion, the code that was identified (P1412), was not recognised from the list that the program recognised as generic codes, but a brief search on Google soon identified the fault as being a 'Frozen Exhaust Gas Recirculation- Valve'. In my experience, these are often troublesome, and athough simple to replace, are quite expensive. Fortunately on this occasion, this error seems to have cleared, and in the last week the fault has not recurred, although I will remain vigilant and keep an eye on the lamp.

Screenshots of hardware and software.

ELM Interface.
This little device contains an ELM327 chip, that functions as the
interpretor of the OBD signals to RS232

Engine off.
When the interface is connected to the computer and to the car,
there are some simple checks that are performed to ensure that
all is well before diagnostics are started. Once these pre-
flight checks are complete, the diagnostics can be started.

Once the engine is started, then the software should be put 'on-line'
This enables the diagnostic tool too read and display the data as it is received.

Live data.
This displays the data in text format, with each type of reading categorised,
so just the figures of interest may be viewed.

Freeze frame.
This enables the relevant metrics that were measured at the time that any fault-
code was identified, and may be used to further diagnose the causes of any failures.

This page lists any error codes that have been identified by the ECU.

From this page, a simulated dashboard may be viewed, but also enables the engineer
to see precise readings that are being measured in real-time.

Useful Links:

The information contained upon this page is supplied in good faith, and to the best of my knowledge is accurate.
However, I accept no responsibility for damage or injury, however caused, due to the use of this data.
The information has been gleaned from numerous web sources, and from my (limited) knowledge.