An important topic in automotive trade is diagnostic techniques for MOT.
Diagnostic systems in the automotive, have been existing in a different state of technical complexity. This has been since the first vehicles
were invented.
Over the years, fundamental changes have occurred. The most basic visual inspections have been improved.
This has been done through the introduction of electrical measuring systems, which enhanced the scope of the diagnostic procedures.
This has been implemented with effective tools with electronic systems. For example; an inspection of the ignition system.
With this tool there are two different diagnostic methods, the onboard (OBD) and offboard diagnosis. The control units are constantly checking their own condition and the condition of the controllers surrounding in self diagnosis mode.
The OBD, continuously analyses the vehicles emission data. With this tool the control units, also store the malfunctions. This is to allow an investigation of the problem at the garage.
How to access the stored code
To access the stored code, a tester needs to analyse the code of the control units.
Diagnostic systems on the older version vehicles use a light. Either, as internal warning lamp, e.g. the engine control unit lamp in the vehicles dashboard, or as an external device. Flashing codes, indicate the malfunction and isolate the faults location.
Where as, advanced vehicles with different sensors, actuators and several control units, need to have a more precise diagnostic approach.
The flashing codes aren’t very effective and an option with a better fault description is needed. This is why, a trouble code entry in the fault memory is defined by explicit rules and symptoms.
For example; a high voltage condition on the controllers signal input. Which then, the trouble code is represented, so that the tester can evaluate it.
As you can see from the photograph above, the functions are distributed over several control units.
The systems are developed and produced by different manufactures.
As much as accurate diagnosis is a must, a single fault can affect several control units.
Why can a single fault affect several control units?
This is because the in-vehicle cross-linking, which is illustrated.
For example; a sensor fault is detected by a control unit and the monitor programme of the sensor generates trouble codes, in the fault memory.
Other controllers rely on the messages of the concerned control unit, but the messages of this controller are no longer correct or transmitted. Therefore, further control units then generate different trouble codes in their fault memory or turn into fall back mode.
Unfortunately, the offboard diagnostic tool reads further trouble codes, instead of the actual fault, caused by different
monitoring procedures.
Only a small part of the controllers diagnostic services, can be accessed during regular driving.
However, this is a disadvantage of the current approach in term of diagnostic requirements.
Accessing the fault memory of the control units is very limited and in some cases, not possible whilst driving.
The driver has very limited fault information about the vehicles condition if a malfunction appears. This is because the fault information is, or only very limited.
For the driver to evaluate the seriousness of the fault, is only partially possible to see on the dash. Which causes the safeness of driving restricted, as the faults of the integrated sensors are only symbols.
However, over the years the quality of control units have steadily increased and new functions are shared over several controllers.
The present diagnostic approaches disadvantages are:
- Different standards are used over the past years
- During the vehicle is driving only limited diagnostic services are available
- Different control units can be affected by a single fault, caused by the network
The modern diagnostics
The modern diagnostics now transmit messages, between the different control units and the cross-linking. But, is not considered to detect
vehicle malfunctions.
The advantage of the new diagnostic approach, is the usage of the transmitted messages.
The transmitted messages, change between faultless and faulty vehicle status. However, this depends on the condition of the car, as the transmitted messages of sensors and control units are different.
The advantages, over the current offboard diagnostic method are:
- Through a precise presentation of trouble codes. So that no components of the car are replaced on suspicion, which decreases repairing costs and time
- An embedded fault memory in the control units is unnecessary. This is why, the purchases of offboard diagnostic tools are no longer necessary for the MOT and garages
- An advanced onboard diagnostic approach, supplies more precise information about malfunctions and the improvement of vehicles
- Precise malfunction information exists for the driver at any time. Malfunctions are indicated, as soon as a fault occurs.
- The advanced fault detection method, uses the transmitted bus messages as fault indicator. The developed onboard diagnostic tool is able to communicate with each bus member. This means: Smart sensor data are checked for plausibility, by monitoring the transmitted messages on the in-vehicle bus network
- The controller and actuator condition can be enquired, by sending status messages over the in-vehicle bus network
- Incorrect commands from the control units, for actuator or other control units can be detected, by monitoring the transmitted messages on the in-vehicle bus network
- A detected fault, can be presented as a trouble code on a display by the diagnostic tool
The design of the diagnostic tool
For the implementation of the new diagnostic method, it is necessary to develop an interface to the in-vehicle bus system, like the photograph shown below.
As shown in the photograph below, the CAN bus monitor is extended with features and functions for the hardware layout of a prototype diagnostic tool.
A CAN bus protocol, is the Controller Area Network (CAN bus), which is a message-based protocol. This is designed to allow the Electronic Control Units (ECUs) found in vehicles today. There are also other devices to communicate with each other, in a reliable, priority-driven fashion.
Conclusion
As the years are flying by and with technology improving, this has allowed for the automotive business to become easier to check for faults and ensuring the safety of drivers.
It is undeniable, that technology is not only our present but our future and with this, it allows for safer roads.
Ensuring that all vehicles when they have an MOT are checked thoroughly and fixed correctly.
Like in everything, there are many advantages and disadvantages to technology. But I must say that, the modern diagnosis techniques have made a big impact to the automotive industry and drivers.
Don’t be surprised, that in the next 10 years, there will be even better diagnosis techniques.
More articles like this one: Health & Safety Protocols in MOT Testing
Are you thinking of having more Training in the MOT field?
Well look no further!
Here at MTC, we have a range of courses available;
- MOT Training Course, Class 4 & 7 – This course is to become a fully qualified MOT tester for cars and vans.
- Level 3 VTAA – The VTAA course is for people that are skilled in the motor trade and don’t have no formal qualifications.
- MOT Training Courses (Car, Motorbike, HGV)
- Level 1 MOT & Hybrid/EV Training Course
- MOT Managers Courses
- Hybrid Training Courses – Level 1, 2 and 3 (Raise Awareness, Light Vehicles, Buses, HGV, Cars)
