AutoIndustry Insider from the UK is an independent source of engineering information relevant to smash repairrs, driven by technical experts from within the automotive industry.
Thanks to AutoIndustry Insider for giving Paint & Panel permission to reproduce this article on diagnostics in the repair process.
Ever since the advent of electronic fuel injection systems, vehicle diagnostics have been with the aftermarket in one form or another – so than means for more than 40 years. As safety critical systems (airbags, ABS, ESC, e-PAS) as well as multiplexed body systems have become common place, so the requirements of diagnostic systems have increased dramatically.
How does a diagnostic system check for faults?
Just like a computer, the diagnostic system on a vehicle relies 100 per cent on electricity to determine if something is working – or not. Unlike a computer, a vehicle has electro-mechanical, electro-hydraulic and electro-pneumatic interfaces. In addition, unlike a computer, the vehicle is dragging itself along the open ground, attracting all sorts of debris too.
Every single component has an electronic signature – a combination of resistance, capacitance and energy use ‘pulse’. The diagnostic system checks that this combined set of values is in line with the specification, and stores a fault if it does not. The system does a ‘sum check’ – a hexadecimal based data set which as each system it tested should give a pre-defined response, so that the vehicle can literally then declare ‘all systems go’ to commence the journey. That check happens every time the ignition is switched on – and given the number of checks, it takes a mightily impressive short time to complete. The way these values are defined and set is via months of carefully planned testing, introducing known faults and ensuring the electronic system is capable or successfully capturing those events.
The main reason for EOBD and EODB II is to monitor engine emission control system performance. If two faults occur after two uses for the vehicle, the ‘engine check light’ is illuminated. The fault code is eliminated if it is not detected after 40 further uses of the vehicle. However, with EOBD II whilst the ‘engine check light’ may go out, the fault codes remain in the diagnostic system memory. Diagram - © Hyundai Motor Co
In the beginning…
Electronic fuel injection systems very broadly had a coolant temperature sensor, an air temperature sensor, fuel pump signal, fuel injector rail pressure sensor, fuel injector signal, crank position sensor, cam position sensor, an absolute pressure sensor and / or a hot film anemometer (also known as the ‘air mass meter). Very quickly means to measure the air-fuel ratio was added (the lambda or ‘O2’ sensor) giving real time feed-back loop to the engine control module, along with direct ignition for petrol engines and links to the rest of the vehicle too.
That was the migration from deleting the carburettor as a fuel distribution device with fuel injection through to fully integrated powertrain control.
European On Board Diagnostics (EOBD)
Following on from the legislation introduced in the USA, Europe adopted a legal requirement to store faults generated by devices in the engine emission control system (EOBD) and stepped up this requirement with EOBD II to include catalytic converter performance. Throughout vehicle manufacturers have added many more features to this ability to capture fault history, as expressed by the Volkswagen group – their vehicles can track every module inside every car, when it was de-coupled or re-attached to the harness, and when it was replaced. In turn new modules require introduction to the specific vehicle, and can be tracked if they are swapped with another vehicle.
A vehicle is built up in the manufacturing plant, and right at the end of the assembly line all of the software for all of the modules is down loaded, at the same time the vehicle is primed with all fluids. The manufacturer than makes a huge assumption about the vehicle when it is fully built – it will only ever be repaired in one location, and will never move from that spot until the repair is complete.
Do we see an issue for the collision repair business?
Yes. Collision repair occurs in at least two locations inside a shop (outside and inside a paint booth) so requiring the vehicle to be moved whilst partially stripped. Most shops have more than four specific locations (inspection / blue printing, strip / repair, paint, re-build).
In the old days, when electric devices were wired without CAN BUS and fuel injection was rare, the repairers got used to being able to drive the vehicle between the locations, so saving time and physical effort. Now, thanks to the diagnostic assumption, every time the electrical system is fired up and it detects some parts are missing, a fault is logged. For post Euro V emission legislation vehicles, that means the fault is logged in the memory, every time it occurs.
What does best practice look like?
There may be no way of ever getting a collision repairer to keep a vehicle in one place for all aspects of the repair process. Equally, it is less than clear if or even when vehicle manufacturers will ever recognise a repair that takes place in more than once specific location. So this is the practical way around the problem:
- Use the diagnostic system to capture exactly what is wrong with the vehicle before the repair commences, usually before a single part is removed. That will define what is not working as a result of the accident, and what was not working anyway. By all means make this data available to the Insurance company right from the outset.
- Perform the repair, taking care to minimise the number of times the ignition is switched on – even if the engine is not started.
- Use the diagnostic system to verify all systems are working once the repair is complete, ensuring all faults are cleared and noting all actions required to clear those faults. This may mean conversations with the vehicle owner to repair systems not involved in the accident.
Until vehicle manufacturers introduce a diagnostic function to allow a vehicle to be repaired in multiple locations, use of diagnostics is a clear way to provide both Insurance companies as well as vehicle owners better visibility of the vehicle condition, and presents a further business opportunity.