MOT Workshop 22 – Diagnostics Intro

MOT Workshop Magazine

Dream profits or technical nightmares?

It won’t be many years now before some form of diagnostic analysis will become a compulsory aspect of MOT Testing – VOSA are already working within Europe on the subject.

But increasingly on a daily basis we need to penetrate a vehicle’s software systems to repair safety related MOT failure items.

Yet the systems aren’t simple to understand, and until the European On Board Diagnostic (EOBD) output socket was standardised in 2000, the number of different diagnostic leads required made our tool trays look like spaghetti junction!

So where are we now? A real expert in this technology is the Garage Equipment Association’s Chief Executive Dave Garratt, who has agreed to provide our readers with a deeper insight:

While running the risk of boring readers who already have a ‘handle’ on this complicated subject, it’s worth looking at some of the basic issues – starting with the EOBD system.

Every car maker must now use a standardised diagnostic socket, and for emissions related engine management systems, they must use the same computer codes and ‘software’.

For all other vehicle systems, however, there’s no EU requirement for so called ‘protocol’ uniformity – the computerised output from the EOBD socket will be different from one make of car to the next.

So it’s no good a BMW service engineer using his diagnostic equipment to discover why a Mercedes air conditioning unit isn’t working – it simply won’t understand the Mercedes signals!

For dealerships this isn’t a problem since most vehicles in the workshop are their own franchised make. Independents however face real difficulties. To help them overcome this, equipment makers offer equipment which can understand the computer protocol of a range of makes of vehicles – but unfortunately none can offer 100% coverage.

So either garage owners accept a limitation on which vehicles to cover, or spend more money buying different pieces of equipment, and even then may only get perhaps 85% coverage.

There’s another issue, staff competence and equipment sophistication. A highly trained whiz-kid can very effectively use a simple scan tool with no diagnostic capability and find faults quickly – whereas the average technician will need a more sophisticated and expensive piece of equipment with diagnostic capability, and still take longer to find the fault!

Taken altogether this means:

  • The vehicle diagnostic (EOBD) socket was standardised after 2000
  • The EOBD output for emission related faults had standardised protocol after 2000
  • All systems other than emissions will have vehicle specific protocols requiring specialised equipment to ‘read’ the output
  • No diagnostic equipment will work on all makes of vehicles
  • The simpler the equipment the greater skill is required to use it effectively

Scan-Tools … Why do we need them?

Most diagnosticians are well aware of the headaches caused by working on electronic control systems on modern vehicles … ABS (Anti-lock Braking Systems), ESP (Enhanced Stability Programmes), SRS (Supplementary Restraint Systems ­– air bags!) and Engine Management.

Then there’s the well-loved CAN-bus network – the latest computer-technological marvel that car makers use to send digital signals around the network. Even more pain in our brains!

So there’s no choice; to diagnose faults on today’s vehicle systems you need a scan-tool to point you in the right direction – using a multimeter is just possible, but may take some time!

Scan tools used by main dealers use dedicated, up to date, vehicle specific software. Unfortunately, however, it takes time for the Aftermarket Equipment Manufacturers to reverse engineer such “vehicle specific software” and for low volume cars it may not even be cost effective to produce it.

As we’ve already seen, scan-tool software is available, but may only cover approximately 85% of the vehicle park, and purchasing equipment to cover such a percentage, can be expensive.

But at least there’s a cheaper alternative for checking Engine Management systems. If you look through most of the Scan-tool manufacturer’s advertisements you will see many offering “Generic EOBD Software”.

EOBD software?

In 1998, the European Union passed an EU directive stipulating the introduction of the European On-Board Diagnosis (EOBD) for all member countries. This means that all car makers must use a generic protocol, which is available to all scan-tool manufacturers.

The introduction date of EOBD to new petrol-driven vehicles was 1 January 2000, and for production diesel-powered passenger cars an EOBD system applied from 2004. The EOBD system checks components, subsystems and electrical components which are relevant to exhaust emissions which may, in case of failure, cause defined emission limits to be exceeded.

How exactly does EOBD function?

A Malfunction Indicator Lamp (MIL) illuminates when exhaust emission related faults have been detected. When it comes on, the owner should take the vehicle immediately to a garage. A mileage counter, which should be accessible via your scan-tool, records how long the vehicle has been driven with the MIL activated.

All EOBD Vehicles have a generic diagnostic socket, which is located in the vehicle’s interior and must be accessible from the driver’s seat.

By removing the need for ‘vehicle specific’ connection leads (the case pre 1998), this EOBD socket has greatly reduced the cost of engine management diagnostics. The socket provides individual connection to each control unit and/or allows all of the control units to communicate via one wire, known as the K-line. Two terminals are also reserved for can-bus communication, which most manufacturers now utilise for the full vehicle diagnostics.

The readable EOBD faults are standardised and defined in a specific code, known as the SAE code. SAE stands for the “Society of Automotive Engineers” – the institution by which the codes were established. The SAE codes are generic and have standardised fault texts, therefore the software required for your scan-tool to read these EOBD codes is already widely available and although these codes flag-up only emission related faults, they are very useful.

So, now for all cars sold in Europe it should be easier and more cost effective to diagnose faults and service vehicles. However, the EOBD enforcement only necessitates vehicle manufacturers to make generically available the emission related fault codes and not codes from the entire vehicle.

Restricting the trade…

This table clearly indicates that the motor trade is beginning to face a real problem when it comes to properly servicing and repairing modern vehicles – and this is not just confined to independent garages, even dealerships from time to time need to service and repair different makes of vehicle.

All new vehicles have numerous electronic systems incorporating on-board diagnostic software. Without access to the software a workshop will find it difficult to provide a full service. The Automotive Aftermarket’s problem is that the protocol used by each manufacturer’s OBD system is unique; manufacturers are not willing to pass this information on, so forcing equipment manufacturers to ‘reverse engineer’ the software needed.

Reversing the engineering process is never going to be as effective as having the correct protocol available in the first place. The lack of these protocols slows down production, increases equipment development cost and hence the cost of the equipment.

Is it legal?

There are very stringent European laws preventing restriction of trade. And arguably by refusing to share their software protocol secrets with equipment manufacturers, the car makers are in breach of European law. This is why the European Garage Equipment Association are in the process of challenging the car makers on this issue in the European court.

So the good news is there’s a generic EOBD diagnostic socket together with a generic protocol and software available for detecting emission related faults. Whereas the bad news, currently, is that for all other problems both safety related, and the so called ‘comfort’ systems (air conditioning, electric seats and so on) garages will have to rely on reverse engineered equipment that will never be able to offer 100% coverage of all vehicles.

Buying advice:

If you are looking to purchase a scan-tool, first check that the supplier can provide the generic EOBD software, and then look at their full range of vehicle specific software. Do your homework, check your customer base and draw a list of the most widely seen vehicles in your workshop. Ask for a quotation to provide the software needed to service and diagnose the vehicles on your list. You may never be able to afford all the software required, but make sure that the most common vehicles are covered. And finally, make sure your staff is fully trained to make the very best use of the equipment you buy.

NEXT PAGE > Diagnostic Equipment Review



MOT Workshop Magazine

Related posts

Comment on this article