Moving with the times

Where could the MOT be heading?

Published:  11 June, 2015

By Neil Pattemore

The Ministry of Transport Test, the MOT to you and I, has been around since 1960 - even if we should correctly be calling it a 'Periodic Technical Inspection (PTI) to assess a vehicle's roadworthiness'. The original test assessed the basic mechanical safety and control systems and has developed over the years to include a wide range of additional elements that now include seat belts, emissions and other modern functions of the vehicle.

To test these items, vehicle test stations have been obliged to invest in equipment and conform to stringent standards imposed by the national 'competent authority' - now the DVSA, but which was formerly VOSA. This test equipment has gradually become more sophisticated in its design, functionality, accuracy and control to make it easier, and most importantly, faster to use. The ultimate culmination of this has been the possibility to have one-man operation of the MOT test and the automation of the various elements of the test equipment to form a sequential and electronically controlled routine - the complete 'test lane' as it has become known.

Over the years, the test itself and the test equipment has evolved, partly to address changes in vehicle technology but equally to use technology to make the test routine faster and more accurate. However, we have now reached a plateau where the existing test equipment cannot be significantly enhanced and it is not possible to test some of the newer safety and control systems fitted to today's vehicles. An attempt has been made to address some aspects, such as a visual inspection of the malfunction indicator light (MIL) on the dashboard, but this raises two key issues - it can be manipulated to make it look as if there are no faults stored in the system's memory but more fundamentally, this is using the non-standardised diagnostic system of the vehicle manufacturer to test their own vehicle.

These vehicle systems are not monitored in-service and equally there are faults which cannot be detected by some of these OBD systems. Not a good basis for a roadworthiness test, especially when electronic components fail at roughly the same rate as the mechanical parts! The basis of the roadworthiness test is that it should be an independent assessment of the vehicle to show that it continues to comply with the safety and environmental requirements in force at the time of its original type-approval.

This subject has been discussed in detail in the development of the new European Roadworthiness Directive (2014/45/EU) which will come into force on 20th May 2018. This new Directive includes testing via the 'electronic vehicle interface', but does not yet contain the test methods that should be used, or details of the test equipment, even though the Directive states it should:

'... allow the functionality of the vehicle safety systems to be monitored in a way that allows such systems to be tested in a periodic technical inspection environment. This is of crucial importance, especially in the field of electronically controlled systems, and should cover all elements that have been installed by the manufacturer.'

In simple terms, it is unlikely that a simple visual inspection of the MIL will be acceptable, so a scan tool would connect through the 16 pin connector and communicate with the on-board electronically controlled safety systems. This could then establish that the system is still fitted and responsive, but it may need to go further and check for stored fault codes or pending codes. This would alleviate the possibility of manipulating the MIL but would still rely on the vehicle's own system to test itself. It may therefore be necessary to read the sensor values and actuator functions, depending on the systems' design. However, ultimately the best solution would be to conduct 'functionality testing,' as mentioned in the Directive.

This would entail triggering the system and running a test sequence of the system while measuring the functionality using existing MOT test equipment. For example, on an ABS system, the front axle would be placed into the brake tester and then the left and right ABS modulator valves would be triggered individually and the variations in brake force values measured and compared. The same would be done for the rear axle. This would immediately confirm that the system is fitted and responding and that it is functioning correctly.

However, it is also possible to go further. While the wheels are in the brake tester, the existing brake force values/ovality can still be assessed, but if the applied brake pedal force (i.e. the internal brake system pressure) is measured and compared to both front and rear axles (brake force reference values), it is also possible to assess the brake force distribution. This test method would also establish that the ABS pump is working and could check the wheel senor signals. If the steering wheel sensor is also monitored and the pitch/yaw sensor signals are triggered, then the ESP system could also be checked.

The same concept can also be applied to dynamic headlight systems where input signals can control the electro-mechanical light distribution that can then be measured on an electronic headlamp tester. This would allow many of the vehicle's ECSS to be tested without significantly extending the test duration, but it may be possible to go a stage further.

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