Genuine ELM or Clone OBDII Adaptors

The device shown in the previous post is a clever piece of electronics that itself is a small computer. One that is dedicated to working out what standard the car is using and then presenting a standard interface to the computer. If I understand correctly this device was first introduced by a company called ELM and a fantastic concept and product it is. Without it the OBDII interface would still be inaccessible to a home enthusiast like myself.

When I purchased my interface I was unaware of the history and then discovered that, as far as I understand, it is a clone of the first version of the genuine ELM product. Like thousands of others I was attracted by the price but ignorant that it is a copy. It would seem the first versions had not been copy protected like subsequent versions. So whilst the official product continues to develop and address bugs etc the clones probably don't.

The adaptor I purchased did work successfully (although one did fail after a couple of months) but perhaps problems may be experienced in due course. Speed is one reported issue. The ability to interrogate the car fast enough. Reliability as I have found is another.

Some of the current low cost adaptors boast being version 1.5 but from what I have read there isn't currently a version 1.5 from ELM, the architects of the product. The version is therefore misleading and probably refers to the physical package and not the functional operation.

Connecting to the Management Socket

Communicating with the car management requires a cable (or optionally a virtual cable such as a Bluetooth connection) and, of course, a computer. However, there are a few concepts to understand that may help with general understanding of what's happening and the purchase of equipment.

Communication between a computer and a car requires a whole range of things to be compatible. It starts with the function of each pin on the connector, includes voltage and timing of signals through to the more human understandable commands and response codes. For example, the most basic part of the standard, but non the less important, is the physical design of the plug. A standard computer doesn't have one of these so that demands some form of physical adaptor.

Unfortunately, there are a number of different standards in use by car manufacturers that affect the operation of the interface. Fortunately, the connector specification is the same but to work out the rest requires an intelligent piece of electronics to mediate between the car and computer. Shown below is a device I purchased to do the job. But more on this next!

The Management Socket

This is a picture taken from the drivers side door looking up under the steering wheel in my Peugeot 206. The OBDII management socket is with the fuses etc and is the green component on the right.

A Network of Computers

Until recently my understanding had been that there was only one computer on a car and that was the Engine Control Unit. However, it appears that this is not necessarily the case. Some cars may have more and this is an important concept to know when communicating with the car (The airbag system may be one and perhaps the ABS system another and of course there is the locking system etc).

These computers share what is known as a bus and is the connection by which they talk to each other. The communication standard does appear to have evolved over the years but the predominant one now in use would seem to be the CANBUS. The CAN standing for Controller Area Network. (It's quite a revelation to think my car includes a computer network)! This concept of a network of computers (more accurately called controllers because they are computers dedicated to certain tasks) becomes important when understanding the language used for managing the CANBUS.

Standards and the OBDII interface.

Around about 2000 something important happened. The various standards organisations around the world introduced standard for communicating with car computers. Prior to this cars had been using computerised systems but all required their own specialised service equipment. The introduction of standards meant that the same service system could be used on a BMW as a Ford or Peugeot etc.

The standards have been phased in over a period of time so it depends on a cars age (manufactuter, country...) as to whether it has the standardised facilities. In europe, for petrol cars, it was around 2000. For diesel the standards appeared later in 2004-ish.

One part of the standards was where the socket to connect to the car should be sited. This is within 1m of the driver. On one of my cars its in the footwell. On another its in the centre console (hidden but easily accessible under the ashtray unit).

The socket is the OBDII interface and looks like a SCART socket found on most televisions.