Ever felt that you were once a pretty good home car mechanic until all this computery stuff came out? Ever got a check engine light come on and felt you had no choice but to take your car down the local dealership and prepare to be fleeced? Ever wanted one of those gadgets you see the mechanics using which tell you instantly what the fault on your car is? ...or maybe you just fancy a cool gizmo that draws graphs of your 0-60 times, horsepower, fuel consumption, speed, rpm, etc.? Personally they all sound useful to me...

Once upon a time equipment to do this sort of analysis was expensive but these days with open source diagnostics software and cheap OBDII PC adapters becoming available to the masses its becoming more and more like something within our reach. Once again those of us that want to can look forward to fixing simple car faults on their driveway.

What is OBDII?

OBDII is a standardised diagnostics connector present on most modern cars which has a data stream containing lots of information such as known faults, fuel consumption, speed, engine rpm, throttle position, air flow, engine temperature, etc. Not only is this data really useful for tuning your engine and finding out how efficient your driving skills are but you can also use OBDII devices to reset check engine lights etc.

Does my car have OBDII?

Thanks to laws in the USA aimed at making all vehicles repairable by non-dealers the OBDII connector must be fitted to all cars manufactured after 1996 sold in the US. In Europe (as with many things) we copied the Americans but unfortunately 5 years later and as such all petrol* cars sold in Europe after 2001 must have OBDII (*see comment at end about diesels). However these deadlines just mean it's compulsory after these dates, many cars manufactured before this may still have the connector anyway. Additionally even if you purchased your car in the EU, chances are that if your car was available in the states after 1996 you may have OBDII as its easier for the manufacturers to leave it fitted globally than omit it outside the USA.

The best way to confirm 100% if you car has OBDII is look for the connector. Its quite distinctive and is fitted somewhere around the front seats usually by the driver and often tucked away under a panel. It takes a while to locate so be patient as it can be a bit of a hide and seek game. Using a torch check behind ash trays, in glove boxes, by the fuse box, etc. Basically you are looking for something like this:

What do I need to access the data?

Put simply you need two things. A way of converting the data stream from the cars OBDII connector to serial data suitable for reading by your PC, and some software to interpret it.

Most PC software looks for the OBDII adapter on a serial port which can be in the form of a physical COM port on the back of your PC or more conveniently a virtual COM port such as a USB or Bluetooth generated port. Whichever you decide to use you need an appropriate OBDII adapter to connect to it.

OBDII Adapters:

When purchasing an OBDII adapter you need to make sure it is compatible with your vehicle. This means you need either a multi-protocol device or one that understands the protocol your vehicle uses. You can get a good idea of which protocol your car uses (usually either ISO, VPW, PWM or CAN) using this guide on ELM's website (a manufacturer of OBDII conversion chips). Personally I recommend you get a multi-protocol adapter then you wont need to worry about buying another one when you change your vehicle, plus you have the added bonus of helping your friends out and comparing results. Unfortunatly for obvious reasons multiprotocol devices are more expensive so depending on funds you may have to locate the specific adapter for your vehicle.

Looking around theres quite a few sources of OBDII adapters out there, some with software, some without, some wireless, some cabled, some multi-protocol and some single protocol. After deciding if you want single or multi-protocol OBDII you need to figure out if your laptop or PDA (whichever you wish to use) has a serial port and/or Bluetooth as this will affect your options. You can of course buy a Bluetooth dongle or USB COM adapter for your laptop separately but it makes your life somewhat easier if you get the correct interface in the first place as the less separate bits of kit you need to worry about the better.

Another thing worth knowing is most 3rd party software appears to be aimed at the ELM chipset so unless you are completely happy with the software supplied with the device you will need to make sure whatever you buy uses this chipset.

Personally I found the ScanTool.net website to have a good range of reasonably priced devices and since they went to the effort of making their ScanTool software open source using the GPL license it makes me more inclined to buy from them (they will ship to the UK or if you prefer you can use one of their distributors). However their software is rather basic (as is a lot of the free software I've looked at) so you may want to look at devices which are bundled with commercial applications such as Engine Check from Gendan.

OBDII Software:

There's quite a lot of software out there ranging from free applications such as those on sourceforge to full blown commercial packages with every bell and whistle you can imagine including vehicle specific optimisations. ScanTools software list is a good place to start looking as it shows freeware, shareware and commercial software side by side but obviously search engines such as Google will help you out more than anything.

Depending on how much you want to do with your device, the free software may be perfectly adequate; for example if you just want to find out what fault code threw your check engine light on most software will do that. However if you want to do slightly more than that such as plot your horsepower curves and 0-60 acceleration you will probably want to look at commercial software. If you do decide to go commercial, as mentioned above its worth considering that you may get a better deal on the software you purchase it with the OBDII adapter at the same time. Heres some examples of the commercial applications available:

PCMScan

ProScan

EEC Analyzer

EngineCheck

GLM

ScanMaster ELM

Conclusion

Modern engine management systems often frighten off home mechanics which is a shame because they needn't; all that is required is a slightly different set of tools. If you have a laptop, computer experience and reasonable car maintenance skills chances are with an OBDII diagnostics tool you can locate and repair many of the common faults which would normally have you turning to the dealer to fix. Sure these generic OBDII devices wont provide you with all the information the dealers get using their super expensive analysers but more often than not you will get what you need to start fixing a problem.

...and apart from all that, plotting graphs of your cars performance can be very revealing.

(Updated: 10:53, Sun 13th Jul 2008)
Posted by Daniel: 22:32, Sat 29th Dec 2007