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
- 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.
- Autoglass launches ADAS 'Over The Air'
Autoglass has launched the Over The Air calibration solution which adds to its existing ADAS proposition. The combination makes what the company calls the Total Calibration Solution for ADAS diagnostics, coding and calibration.
- Ring: Bulb wall chart
Ring has issued a quick-reference wall chart for 6V and 12V bulbs. The chart features images, ECE references, dimensions, technical drawings and part numbers for over 600 replacement bulbs.
The chart also includes information about Ring’s xenon HID range, which features well-established references as well as the newer D5 bulb that is now being fitted on a growing number of vehicles. Research from Ring suggests that xenon HIDs should be replaced every three years, to prevent a drop in light output and maintain visibility for drivers.
Ring’s Vehicle Lighting Product Manager Matthew Flaherty said: “The chart gives a quick reference guide for a wide range of bulb references. We’ve included some of the newest bulbs now being fitted to vehicles, including up to date HID references and the latest in performance upgrades. Our aim is to help technicians identify the correct replacement and offer potential upgrades, so that they can give their customers the best bulb for their vehicle with up to date information and options.”
To order the chart, call Ring’s UK Customer Service Team on 0113 213 7389 quoting part number CAT1248
- Ben Impact Report highlights 29% caseload increase
Industry charity Ben saw a 29% year-on-year increase in the number of cases managed by its support services team, according to the organisation’s annual Impact Report for 2018-19, which was published this week.
- The secret behind Top Technician: Process
I guess it’s just human nature to want to take a peek behind the door that says ‘Private, Members Only’. What could be so special, and what are we missing out on? It’s with that in mind that I’m writing this article. In the next four minutes I’ll reveal what goes on behind the scenes in the Top Technician technical tests, and what it takes to diagnose a vehicle in 20 minutes. You’re going to love it!
I first became involved with Top Technician as a judge in 2008, I was hooked from the start as it epitomised everything I loved about the industry. Watching dedicated technicians work progressively through each technical test was a thing of beauty. Not knowing who would win, as so few points separate most entrants, would keep me on a knife edge throughout the day.
Here’s the deal though; While this is a competition, the skills used to win are exactly the same skills that need to be displayed in your workshop every day. These skills ensure your diagnosis happens in a timely manner, and you can bill all of your diagnostic time. Not only that; Anyone considering taking a Diagnostic Technician or Master Technician assessment needs to display the same skillset. There’s a blueprint for diagnostic success, and if your follow it then you’ll progress in leaps and bounds.
What’s in a technical task?
There are a few core skills that a technician should possess, so each technical task is designed so that a competitor can display the following:
