Cut to the chase
Damien Coleman from Snap-on discusses how preparation can lead to easier diagnostics
Published: 28 August, 2018
Many modern systems, such as common rail diesel injection, can appear to be so complex that they seem to operate by magic. Over time, such systems are only going to become more and more complex, so understanding them means you can gain a head start on their repair.
You can be presented with a seemingly endless amount of data relating to fuel pressure feedback, fuel pressure control, cam/crank synchronisation, measured mass airflow, injector flow correction feedback, and many other areas.
However, if you prepare yourself with a fundamental understanding of the system and all data available pertaining to the fault, a systematic approach to the fault-finding procedure can be carried out.
Data overload
Figure 1 shows the live data returned from a common rail diesel injection vehicle with an EDC16 engine management system.
There is an enormous amount of data available from these data parameters, which can allow you to ascertain the nature of the fault. The actual operation of the fuel system can be compared to the desired system operation and using the data, a decision can be made on the condition of the system and where a fault (if any) may be.
An oscilloscope is another important tool when investigating a fault with such a complex system. Figure 2 shows an oscilloscope waveform from an Audi with the 2.0L common rail engine. The yellow trace is the fuel rail pressure sensor voltage (feedback) and the green trace is the current flow through the inlet metering valve (command). The waveform was captured during a wide open throttle (WOT) condition.
This image alone tells us that the fuel inlet metering valve is a normally open valve. The engine control module (ECM) decreases the duty cycle when the required fuel pressure is increased. This allows less current to flow through the solenoid and the valve is allowed to open, which increases the fuel pressure measured at the fuel rail.
Full analysis
When the fuel pressure demand decreases, the duty cycle control from the ECM increases. This allows more current to flow through the solenoid which results in a reduction of the fuel pressure. Duty cycle is often referred to as pulse width modulation (PWM) control.
The duty cycle control on the ground side of the fuel inlet metering valve can be analysed using an oscilloscope, as seen in Figure 3. The waveform below displays the fuel rail pressure feedback voltage (yellow trace) and the fuel inlet metering valve duty cycle control from the ECM (green trace).
The oscilloscope is connected to the control wire for the fuel inlet metering valve. The technician must be mindful that this is the ground control circuit. System voltage on this wire indicates open circuit voltage. The diagram in Figure 4 shows the best method of connecting this set-up.
By careful analysis using serial (scan-tool) and parallel (oscilloscope) diagnostics you will now be in a position to identify the area of concern accurately and in a timely manner. Knowledge, together with the right equipment and experience therefore benefits technicians by leading to a reduced diagnostic time and an easier fault finding method, rendering these complex systems much less so.
TT Archives: Top Technician issue ten 2016 | www.toptechnician.co.uk
- A reality check
This year’s summer was good, but as usual, was over too quickly – so back to work and a reality check!
However, during my summer travels some of today’s necessities of life were conspicuous by their absence. I hired a car, only to discover that the USB connection I needed to use to charge my phone and link to my favourite music playlists didn’t work. The local radio station’s dubious choices in music didn’t help relive the tedium, but when I got to the hotel my woes were compounded when I discovered that they wanted to charge a ridiculous amount to use their wi-fi – I mean seriously, who in their right mind can justify charging hotel guests for basic wi-fi – unless the hotel is run by Ryanair (who seem to want to charge everyone for everything), which it wasn’t.
So, with no wi-fi in the hotel room, I had some time on my hands, so I started thinking about the connections we expect in today’s connected world and in turn what connections are needed to run today’s workshop. This got me thinking about the problems it would face if these connections were either expensive, were restricted, didn’t work as they should or didn’t exist at all.
Form over function
Back in the 1990s I remember well being handed a new portable diagnostic tool which could connect to the internet via the mobile phone networks. Subsequently, it was able to conduct remote and bi-directional diagnostics on a vehicle anywhere in the world, when the vehicle was also connected to the internet – effectively ‘PC anywhere’ technology. However, I also clearly remember complaining to the development engineer within a couple of minutes because the functionality was too slow. He was visibly shocked and was clearly offended by my negative feedback on what was his pride and joy. Then I realised what had made me comment negatively – it was not the impressive technology, but the speed of use and the corresponding ability to run the diagnostics I wanted to conduct. In IT terms, this is referred to as system ‘functionality’ and ‘non-functionality’. Simply, the ‘non-‘functionality’ is the design of the system and the ‘functionality’ is what it can deliver. It might be easier to remember this in layman’s terms as being ‘Form over function’.
When applied to the workshop, this directly applies to a wide range of electronic connections that are needed to support your day-to-day business, and if these connections do not work as needed, how this can quickly and detrimentally impact your business activities.
Don’t miss the ‘bus’
The ubiquitous Universal Serial Bus (USB) connection is a good example. A ‘bus’ within a PC are wires that transfer data between components inside the computer, or between the computer and its peripheral devices. We have all come to use this connection for a wide variety of tasks, from using it as an auxiliary power source for many different gadgets, to a vital communications port for various functions such as printers and other data transfer requirements. However, if it does not work correctly, physically or electronically, then simple tasks suddenly become major issues.
This wired technology has moved on and most of us are now connected by wi-fi in the office environment, but increasingly also in the workshop to connect diagnostic tools to the internet. Data transfer speeds depend on the technology used and the latest generation (soon to be 802.11ax) is super-fast, which becomes more important as software updating of vehicles involves the transfer of massive data files. Generally, wi-fi connections work well, but when they suddenly stop working, it is more difficult to diagnose as it is not a physical connection than can be more easily tested. This may happen after a software update and a recent experience showed me how simple a problem can be, but how difficult it was to discover, when my PC was updated and a simple setting was changed. Over three hours of technical support was needed to discover that it was a simple tick-box setting which needed to be re-enabled. These wi-fi problems move into understanding the IT environment of certificates, configurations, permissions, log-in and passwords between the router and the various connected devices, without even starting to consider the wider communications providers that connects your workshop to the wider world.
Have a cookie
This leads me onto an increasing communications requirement which has become a fundamental part of our day-to-day lives, from both the personal and business aspects – the internet. If there is ever a perfect example of living in a connected world, this is it. However, if you think about the wide-ranging possibilities that the internet supports, do you ever stop to think about the technology behind what is happening to understand the control mechanisms that are needed for it to be safe and secure? If you visit a website, not only are there likely to be cookies tracking your choices and mapping your activities, but there will be certificates being exchanged to ensure secure communication. This may extend to log-in criteria and passwords, or may be implemented by the service provider whose website you are viewing. This becomes particularly important when you are paying for something online.
In simple terms, all this is a form of coded access, but this works not only to ensure the correct access rights, but more importantly, to stop anyone who does not have the valid access rights from interfering or monitoring what you are doing.
Control
What then does all this lead to at the workshop level? In terms of the technology of the equipment, then it is developing to be both more reliable and faster, but the same cannot be said of the beloved OBD connector, which is not only restricted in terms of speed, but will become restricted in terms of access without the correct roles and rights authentication which requires certificates from the vehicle manufacturer. As the manufacturer controls this certificate, then it becomes ‘He who controls the connection, controls the function and ultimately the business’, so the workshop of tomorrow needs to worry most about a connection that they have no control over, but which will control their business.
Time then to sign up with one of the aftermarket associations and join the fight to protect access to the in-vehicle data!
xenconsultancy.com
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- blueprint for technical success
Have you ever wondered why it is that some technicians have an aptitude for complex diagnosis? You know the type of tech I mean. They take the seemingly unfixable, dive headlong into diagnostic battle and emerge triumphant time and time again.
Not only that, but they’ll often do so in a time that makes other techs look on in awe! What’s their secret? And more importantly, can you emulate their success? Well, I’ve got some great news for you. You can, and knowing what to do is easy. All that’s required is that you look to the past. History is a great teacher.
I turned 50 this year, and one of the few benefits of increasing age is the ability to spot patterns, and patterns of actions that when followed culminate in your success. Patterns for success surround us, but sometimes you can be a little too caught up in the urgency of the now to spot them.
I’ll show you the patterns great technicians use to triumph in the world of technical diagnosis, and how you can do the same. It’ll be your blueprint for success.
You’ll like the blueprint. You’ll appreciate its simplicity, recognise the logic, and in all probability nod along as you read, agreeing with the steps that need to be followed.
Here’s the deal though: You’ll need to implement it. Knowing the blueprint is easy, but knowing what to do doesn’t get the job done. It’s all in the implementation, and that starts with you taking small steps to achieve positive changes each day. Don’t forget one of my favourite sayings: “Progress NOT perfection.”
I’m as much a fan of the latest technical gadget as the next man. I also love “cool” test techniques, but I’ve noticed that myopic focus on these can often be to the detriment of the long-term technical success of a technician. I’m not saying that you shouldn’t explore “shiny” elements in our craft, but you’ll find huge benefits in building a solid foundation that can be executed on every diagnosis. What do you need to “do well” then? Just these five steps.
Step one – Systemise to win
There’s always a right and not so right way to attack any given fault. One fundamental element is to have a defined system that all technicians use. Without a rigorous system to follow, your diagnosis could be doomed before you start. Here’s an outline of our diagnostic system that just works;
1 – Thorough questioning of customer, establish change point
2 – Confirm and experience fault with customer
3 – Visual inspection for obvious issues
4 – Retreive fault codes, and gather data on what’s required to raise them
5 – Inspect serial data. Note what looks wrong
6 – Research technical bulletins and any technical information required for accurate testing.
7 – Document what’s wrong and possible causes
8 – Form plan and prioritise relevant tests
9 – Carry out tests and draw conclusions
10 – Bypass test to prove the conclusion where applicable
11 – Repair as required.
12 – Carry out postfix operations i.e. component coding.
13 – Carry out tests to confirm repair
Use our process and you’ll definitely be putting your best foot forward.
Step two – Sound electrical knowledge
Now you know what a great process looks like the next part of your blueprint is your understanding of automotive electrics. How quickly you can decide what to test, what tool to use, and what the answer should be is an essential skill that pays huge dividends once learnt. Key elements include:
1 – Becoming comfortable with relationship between volts, amps and ohms
2 – Using voltage drop to accurately find circuit faults
3 – Series and parallel circuit diagnosis
4 – Interpretation and use of wiring diagrams
5 – Fundamental mechantronics test knowledge
Armed with these, you’ll be able to find wiring faults, diagnose sensor and actuator circuits as well as build entry-level bypass tests to confirm your theories. These are skills you’ll use on the majority of diagnostic repairs. Learn these and you’ll reap the rewards for your entire career.
Step three – Oscilloscopes; One tool to rule them all
A little dramatic I know, but understanding how to use an oscilloscope competently is a game changer. It will bring to life all that has been learned in Step two (auto electrics), and when used skilfully will display this in a way that can confirm or deny faults in vehicle circuits, sensors and actuators.
As an example, take just one quick connection (less than a minute on most petrol cars) to the switched side of a manifold injector and you’ll know;
1 – That power supply to the injector is not open circuit
2 – The ECU has control of the injector and is commanding fuel delivery
3 – Time taken for fuel delivery to commence (injector opening)
4 – Integrity of injector ground circuit
5 – Time takes for fuel delivery to cease (injector closing)
Add some additional test points for injector power supply, current and rail pressure (another couple of minutes) and you’ll confirm the integrity of the positive supply to the injector, the injector winding, and a great test for a quick look to ensure the injector is delivering fuel once open. Like I said - It really is one tool to rule them all!
Step four - Generic systems knowledge
With steps one through three in place you’ll now have the foundation knowledge to explore vehicle systems. This can be a little intimidating as there are so many systems and so much to see, which is why we advise attacking this in bite-size chunks. Your goal here is to become familiar with generic items that broadly apply to a wide cross-section of vehicles. While there’s no substitute for formal training, taking a few minutes on a regular basis to self teach is invaluable. Here’s some things for you to try:
1 – Pick one system to start with. E.g. petrol engine management
2 – Select a book or watch a video for some foundation learning
3 – Focus on one part of a system. E.g. Loads sensors
4 – Inspect serial data for MAF and MAP sensors across various load and speed ranges
5 – Scope MAF and MAP sensors across load and speed ranges
6 – Record your results and repeat on different vehicles on the same components
7 – Repeat points one through six on different components
Do this on a range of vehicles and systems and you’ll become incredibly familiar with what good looks like, as well as raising many questions that we’ll answer when you attend our training.
Step five – Manufacturer information and tooling
There’s one final piece to this part of the puzzle and that’s using the using the best information and serial tools.
While I understand that generic information and tooling has its place, I also have too many real-world examples where my blood pressure would have been dramatically raised were it not for O.E. information and diagnostic tooling. My advice here is straightforward;
1 – Select one manufacturer initially
2 – Become intimately familiar with their information system
3 – Learn to use their wiring diagrams
4 – Explore their technical service bulletins
5 – Use their repair procedures
6 – Substitute a generic serial tool for the O.E. tool for a month
7 – Explore all the serial tool has to offer
We’ve been training technicians like you to use this equipment for many years. It’s had too much of an impact for those that have grasped the nettle for you not to give it a go.
You now know what it takes to begin the road to technical success. All you need to do is start. Taking regular steps, and before you know it you’ll have not only reduced your stress but your time to a first time fix as well.
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