No Smoking!

Karl Weaver tests the old adage ‘where there’s smoke, there’s possibly a problem with the mass airflow sensor…’

Published:  22 May, 2018

There’s nothing I love more than picking up an automotive magazine and reading a good case study. Occasionally they may be talking about a specific fault you’ve seen before. Sometimes as you’re reading through the symptoms and evidence you can’t help but make your own diagnosis and see if you were right.
    
The most engaging ones for me are when it’s not a common fault and you follow the diagnostic process of the writer. I find I always gain ideas and tips from a lot of these articles which assist me in improving my diagnostic success rate. In my previous articles I’ve emphasised the importance of training, whether it be in the classroom or via CPD. Another key thing is to learn from our mistakes and recognise our weaknesses. If we don’t do this, how do we improve?

Patterns
Over the years we have developed a good reputation for diagnostics which regularly brings in new customers. So when someone phones and says “I’ve got a light on and I’ve been told that you’re the man to see,” we have to make sure we get it right. When that sentence is closely followed by “my local garage has replaced some parts but the light has come back on,” we can quickly guess what’s coming next; “Can you fix it? I’ve already spent hundreds, how much is this going to cost me?” We’re not guilty for the previous garage’s failure to diagnose the fault but if we agree to take on the job we are compelled to get it right and so we should be. When you do get it right, is it necessary to stick the knife in the other garage’s back? Of course not! We always try to be positive and stick to explaining why we were successful with the repair rather than why the other garage failed. At this point you’ve already won the customer’s confidence in you.
    
So we learn from our mistakes and we can also learn from other people’s mistakes. With this in mind, over the last few months I’ve looked for a pattern in why misdiagnosis seems to occur. The obvious answer here is lack of training and skill but the frustrating thing with a lot of these jobs is if the technician had just stopped for a minute and thought about it, they probably would have found the fault.

Information
I’ve picked a handful of the last few jobs where this is the case and I’d like to share them as case studies.
    
The vehicle in question: 2012 Ford S-Max 2.0 Diesel. The customer’s complaint: Engine malfunction light on and lack of power. Previous work carried out: New genuine Ford mass airflow sensor fitted.
    
As always, we gathered as much information as possible from the customer. A key piece of information here was that the vehicle starts fine with no light on and performs normally until you accelerate hard or go uphill. He said his local garage plugged it in to their computer which told them it was the mass airflow sensor. They replaced this but it didn’t fix the fault.
    
We read the DTCs from the powertrain control module (PCM) and then road tested the vehicle to confirm the fault. The DTC was ‘P00BD-00 Mass or Volume Air Flow “A” Circuit/Range Performance – Air Flow Too High’ Yes, that’s a bit of a mouthful but there is an important clue in there. In this case we cleared the code just to make sure it returned when the symptom occurred which it did.
    
At this point there are several ways to go dependent on what you have access to.

Option one:
Log in to manufacturer’s technical portal and check for any bulletins relating to this code and maybe even download test procedures for it.

Option two:
Create your own test plan which should include inspecting and testing all components and systems that are linked to the engine air intake system.

Option three:
Load the parts cannon, aim and fire until the light stays out.

Someone has already tried option three  so let’s forget that. We don’t all have option one but I highly recommend having it in place as it can be extremely useful and save a lot of time...   

...We chose option two.

Sensors
As we were already on road test it was an ideal time to look at some PCM serial (live) data. We opted to look at the mass airflow sensor (MAF) and boost pressure sensor/manifold absolute pressure (MAP) sensors signals. Most diagnostic tools will give a ‘desired’ and ‘actual’ reading of MAP. Desired is the reading the PCM is requesting and expects to be seeing and actual is what is actually being measured. This regularly proves to be very handy when diagnosing any air/boost related faults. Straight away we could see that when you tried to accelerate, the actual boost pressure was considerably lower than the desired pressure. There are many possible causes of low boost pressure. We tend to start with a pressurised smoke test to the induction system. This is
a very effective way of finding both internal andexternal leaks.
    
We connected the machine directly after the nice shiny new mass airflow sensor (See Image 1 and Image 2), and within a matter of seconds we could see smoke coming from the intercooler area. A closer inspection revealed a split in the intercooler hose. A new hose was fitted and the vehicle was retested which verified a successful repair. I would love to be writing all about measurements taken with oscilloscopes and lots of technical stuff but it simply wasn’t necessary here.
    
Could the previous garage have fixed this one (see Image 3)? More than likely, yes! A thorough visual inspection to the induction system would have revealed it without the smoke machine due to the amount of oil residue around the hose.

Experience
The clue was in the DTC all along – ‘Air Flow Too High.’ It could mean that the air flow sensor is faulty and is reading too high but it’s important to stop and consider what could make the reading too high. In this case simply too much air flowing through it because it’s leaking back out the other side. Experience gives you the understanding of the PCM’s logic in what would make it flag that fault code. It’s also a fair point to ask why the DTC said “boost pressure too low.”
    
Experience has taught us that different manufacturers have different ways of saying the same thing and that is why I emphasise on reading the fault code carefully. For the same symptom some manufactures may use the fault code text ‘boost pressure too low,’ ‘boost pressure negative deviation,’ ‘turbine under-speed,’ the list goes on but this one: MAF/MAP correlation incorrect”’(seen on Land Rover) hits the nail on the head! The logic within the PCM relies on tables of pre-set data for comparison. It knows that if the engine speed ‘X,’ if the air mass entering the engine is ‘Y’ then the manifold pressure should be ‘Z.’ There is a set error tolerance either side to allow for slight deviation and when this is exceeded. For example, when air is passing through the mass airflow sensor but escaping before the manifold, then the DTC is set and as in most pressure related faults the engine power is reduced (see image 4).


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  • Inject some knowledge  

    At the heart of fuel delivery is the injector. If there is a single focus point that has helped reduce emissions and boost performance it’s the injector. Despite this, we don’t pay it enough attention, and I include myself in this critique. Let me qualify this by asking a rhetorical question; How many of you have injector bench test capability?

    I do, but freely admit to not giving it a more prominent position in fault diagnosis. I am going to expand later just how intrusive testing should be conducted. To begin, a short trip down memory lane won’t do any harm in understanding basic problems.
        
    Injector problems started in earnest when lead was removed from gasoline. The Nissan 1.8 turbo and Austin Montego 2.0efi were two of the most problematic examples. Both used 15ohm single event saturated triggering with approximately 1-amp peak current. This was back in the days when we were not measuring current nor did we have an injector bench.
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    A lot has happened since then. The key to ideal fuelling is in reducing the lag or dead time in injector response to PCM control. As engine power increased and turbos became almost mandatory, more fuel was required. To achieve these aims, opening times were increased to a point where they were in danger of colliding at high engine RPM. We are still talking port injection here, fuel pressures crept up to four-bar and high flow injectors started to be introduced.

    Current ramping also changed to peak and hold with peak values of around 4-amps. For the time being things stabilised, with little or no obvious common injector problems. The next challenge manufacturers faced was to reduce the internal mass of the injector components. In plain English they got smaller, lighter, less robust, and with lead free legislation less reliable. Remember Fiat iaw injectors?

    Precise control
    As EU emission rules became more stringent, the need for even more precise control was inevitable, and along came direct high-pressure injection. Lets explore the variables of fuel transportation, variable delivery pressure 50-200bar, multiple injector strikes and adjustable delivery timing. Peak current now reached 10-amps and pwm switching became commonplace.
    We now have gasoline injection that more  closely resembles diesel injection protocols. They also bring similar problems. Fuel is no longer delivered through the inlet port, leading to a build up of carbon behind the valves. This effect, the critical swirl in the cylinder, is essential for complete combustion. Filtration and fuel quality are now major considerations for reliability.

    Hostile environments and anomolies
    Injectors are now mounted in a more hostile environment, more pressure, more heat, more tip carbon. So, the need for testing and cleaning has come full circle from the lead-free era. A major problem here is the stress caused to the injector body by techs not using the correct removal tool.

    Remember the comments on lighter internal mass; This means than bending stresses during removal leads to intermittent combustion anomalies. I do love that word, it more accurately describes incomplete combustion, often without any credible serial fault data.

    New fault phenomena
    Now let’s notch it up a bit and introduce some new fault phenomena. The internals are so light they can suffer mechanical failure, and the closure spring can break. The internal filter basket has been moved to a more central position, resulting in inaccessibility for replacement.

  • Issues of rotation 

    I received a phone call from another garage: 'We've seen you in the Top Technician magazine and are wondering if you would be interested in looking at an ABS fault for us?' The call went along the usual lines, can the symptoms be recreated? What is the repair history? The vehicle was booked in for me to take a look.

    The car in question was a 2011 Honda
    CR-V, which had been taken as a trade in at a local garage, the fault only occurred after around 50-70 miles of driving, at which point the dash lights up with various warning lights. The vehicle had been prepped and sold to its new owner unaware a fault was present.

    Fault-finding
    After only a few days the fault occurred and the vehicle returned to the garage. They had scan checked the vehicle and the fault code ‘14-1- Left Front Wheel Speed Sensor Failure’ was retrieved. On their visual inspection, it was obvious a new ABS sensor had already been fitted to the N/S/F and clearly not fixed the fault. Was this the reason the vehicle had been traded in? They fitted another ABS sensor to the N/S/F and an extended road test was carried out. The fault reoccurred. This is when I received the phone call; the garage was now suspecting a control unit fault.
        
    My first job was to carry out a visual inspection for anything that was obviously wrong and had possibly been over looked: correct tyre sizes, tyre pressures, tyre tread and excessive wheel bearing play. All appeared ok. The ABS sensors fitted to this vehicle are termed 'Active' meaning they have integrated electronic and are supplied with a voltage from the ABS control unit to operate. The pulse wheel is integrated into the wheel bearing, which on this vehicle makes it not possible to carry out a visual inspection without stripping the hub.

    Endurance testing
    With the vehicle scan checked, all codes recorded and cleared, it was time for the road test. Viewing the live data from all the sensors, they were showing the correct wheel speed readings with no error visible on the N/S/F. The road test was always going to be a long one, fortunately at around 30 miles, the dash lit up with the ABS light and lights for other associated systems; the fault had occurred. On returning to the workshop, the vehicle was rescanned, fault code '14-4 - Left Front Wheel Speed Sensor Failure’ was again present. Again using the live data the sensor was still showing the wheel speed the same as the other three, so whatever was causing the fault was either occurring intermittently or there was not enough detail in the scan tool live data graph display to see the fault. It was time to test the wiring and the sensor output signal for any clues.
        
    Using the oscilloscope, the voltage supply and the ground wire were tested and were good at the time of test. I connected the test lead to the power supply wire and using the AC voltage set to 1V revealed the sensors square wave signal. Then rotating the wheel by hand and comparing the sensors output to one of the other ABS Sensors, again all appeared to be fine. A closer look at the signal was required, zooming in on the signal capture to reveal more detail; it became easier to see something was not quite right with the signal generated by the sensor when the wheel was rotated. With the voltage of the signal remaining constant, a good earth wire and the wheel rotated at a constant speed the signal width became smaller, effectively reporting a faster speed at that instant, not consistent with the actual rotational speed of the wheel. It was difficult to see the error, zooming out of the capture to show more time across the screen it could be seen that this appeared in the signal at regular intervals, although not visible all the time because it was such a slight difference. Using the cursors to measure between the irregular output and counting the oscillations, it was clear that it occurred at exactly the same interval every time. It had to be a physical fault on the pulse wheel.
        
    This meant a new wheel bearing was required. The vehicle was returned to the garage as they wanted to complete the repair, a new wheel bearing was fitted and extended road testing confirmed the vehicle was now fixed.

  • Highs and Lows 

    When faced with diagnosing a fault, in order for us to be able to test the system it is crucial we understand the system’s layout, components and function. We recently faced a fault in a system we had little experience on, so it was an ideal opportunity for a bit of studying.

    Technical information is readily available from many sources, be it manufacturer or generic information, and does not take too long to find. While Google isn’t really a substitute for diagnostics, in situations like this it can be very useful for generic information. The fault on this vehicle turned out to be something so trivial I won’t bore you with it. What I would like to share is the valuable information I picked up along the way.

    Main purpose
    Exhaust gas recirculation (EGR) is nothing new, it’s been used on petrol and diesel engines for many years and while layout and control has varied in design the principle has remained the same. It is important to understand that manufacturers use different methods and configureuration, and for this article I’ve studied several and have tried to demonstrate a generic system.

    The main purpose of EGR is to reduce the level of harmful Nitrogen Oxide (NOx) gases emitted from the vehicle’s exhaust. NOx is present in exhaust emissions due to high combustion temperatures and pressures. Under light load/cruising conditions the EGR system directs a proportion of the exhaust gas back into the engine’s air intake. This reduces the oxygen levels which in turn reduces combustion temperature resulting in a lower NOx emission. When power is required from the engine the EGR system closes to insure a more efficient combustion (see figure 1).

    EGR on/off
    This is the conventional system in its closed (off) position.  During operation exhaust gases are taken from the exhaust manifold (pre-turbo), passed through a cooler (10) up to the EGR Valve (6). The cooler is a heat exchanger that not only uses the engine coolant to cool the gases to increase the mass but utilises the heat to warm up the coolant faster which helps the interior heater warm-up faster. The EGR Valve (6) can be either electrical of vacuum operated. The  powertrain control module (PCM) commands the EGR valve to open by a specified amount dependent on engine conditions (see figure 2).

    Some EGR valves have a position sensor that provides feedback to the PCM to ensure the correct position has been achieved. In a system where the EGR valve is not equipped with a position sensor, the PCM monitors the Mass Airflow signal in order to regulate EGR flow. This is achievable due to the fact that as the EGR valve is commanded open and gases start to flow, the air flowing in to the Mass Airflow Sensor will decrease. The calculation is made using tables of data (mapping) within the PCM’s software. Understanding this is crucial when diagnosing running faults as a fault in the Mass Airflow can easily affect the EGR system and vice versa.

    Understanding and diagnosing airflow and EGR faults I find can be easier if you look at it pressure differential. If air is flowing through a tube with a restriction in it, the air pressure after the restriction will always be lower than the pressure before the restriction. The difference in pressure will vary depending on the mass or pressure of the air and the size of the restriction.

    Air intake/throttle flap
    The air intake/throttle flap (see figure 3) generally defaults to the fully open position while the EGR valve defaults to the closed position. The purpose of the flap is to reduce the pressure on the engine side. As the intake flap starts to restrict the airflow, the pressure decreases to a pressure lower than that of the EGR pressure and the EGR gases start to flow into the engine’s air intake. If the exhaust gas pressure was slightly lower than the air pressure entering the engine then the gases would flow in the wrong direction.
        When in good working order this system serves its purpose. However, due to the fact that there is particulate matter in the exhaust gases, the system and components will slowly become blocked, causing reduced flow and valves starting to jam or not seal correctly. The air intake system often contains oil residue from the engines breathing system and slight oil loss from the turbo itself. When this oil is mixed with the particulates in the EGR gases it makes a very sticky gunk that starts to block the inlet manifold and intake ports.

    When the engine is under load and turbo boost pressure is required, the EGR valve needs to close and seal. If an EGR valve isn’t sealing correctly when closed then boost pressure will be lost into the exhaust system. The lower boost pressure and reduced oxygen level affects the combustion which in turn causes more particulate matter which only adds to the issue. If the EGR valve is stuck wide open then in most cases the engine will barely run.

    High pressure system    
    Euro 6 was introduced in September 2014 which demanded much tighter emissions than previous which required an advance in emission control technology. While the precise control of the fuel side of the engine management system has gained precision with higher fuel pressure and multiple injections within the cycle, the air intake, exhaust and emission control systems have too. Most manufactures use a high and a low pressure EGR system.  Prior to this most EGR systems were relatively simple and fell under the ‘High Pressure EGR’ title (see figure 4 and figure 5).

    The high pressure system is similar in layout to previous systems but serves a slightly different purpose. The system is only used during the warm-up phase of the engine from cold start. There is a pre-turbo passage from the manifold directly to the high pressure EGR valve (6). As the system is only used in the warm-up phase there is no need for a cooler. In this particular system there is a distribution channel that directs the gases equally into each inlet port. The purpose of this system is to raise the intake air temperature in order to improve combustion and reduce the warm-up time for the catalytic convertor/NOx storage catalyst (7) allowing them to function sooner. Once at operating temperature the system is pretty much redundant.

    Low pressure system
    The low pressure system (is active under most engine operating conditions and its purpose replaces that of the older systems- to reduce NOx gases (see figure 6). A proportion of the exhaust gas is collected after the Diesel Particulate Filter (8) and passes through a Wire Mesh Filter (9), through the EGR Cooler (10), up to the Low Pressure EGR Valve (11). The EGR valve then controls the flow through a channel up to the intake side of the turbocharger. The wire mesh filter ensures there is no particulate matter entering the system and also in the event of the particulate filter substrate breaking up, it also protects the rest of the system including the turbocharger, air intake and engine internals from damage. The cooler reduces the gas temperature which in turn increases the mass allowing a higher volume of exhaust gas to be recirculated. Due to the exhaust pressure after the particulate filter being quite low and also the air intake pressure before the turbo charger also being low there is and Exhaust Flap (12) fitted. By closing this slightly the exhaust pressure increases which causes the gases to flow back towards the turbocharger.

    Key benefits
    These systems usually have between three and four  exhaust gas temperature sensors each placed at key points of the exhaust system and two pressure differential sensors. The first is measuring pressure before and after the particulate filter (to calculate soot loading) and second between the DPF outlet and the point after the EGR valve, before the turbo. Coupling these six signals with the Mass Airflow sensor, the positions of both EGR valves and the intake flap, the turbo variable-vane position and the intake pressure (MAP), using the mapping within the PCM’s software means it can also make all calculations necessary. This provides an extremely high intake pressure and exhaust after treatment control.

    The key benefits of this system are that the exhaust gases are free of any particulate matter which keeps the entire system much cleaner and therefore reliable. The gases are also cooler meaning a greater mass can be used in a more effective way. Finally the gases re-enter the system before the turbocharger, allowing for the increase in boost pressures at lower engine load and RPM.

    Does this make diagnosis harder than before? Not if you take the time to study the purpose of each component and how it works. I’ll openly admit it wasn’t that long ago that I would have taken one look at this system and sent it on its way! Nobody likes being beaten by a job but neither should we have to waste too many hours trying to guess what’s wrong with it, worse still start throwing parts at it. It took me half an hour to locate this info, an hour studying it and a further hour planning what tests I was going to conduct and what results I was expecting to see. What was wrong with it in the end? A faulty sensor confirmed with no more than a voltmeter! After replacing the sensor I wanted to confirm the repair and monitor the function of the components using serial data. Something I highly recommend doing is picking five lines of serial data on every car you work on that requires an extended road test and monitoring them to see how they behave and what effect driving style (engine load) has on them. I guarantee after 10 cars you’ll know what to expect and be far more confident in diagnosing related faults. It works for me!

  • Part two The good and THE GREAT  

    In part one, we looked at the start of the ‘diagnostic process.’ The first steps were customer questioning, confirming the fault and knowing the system and its function. These help the technician to build the ‘big picture’ necessary to repair the vehicle correctly.
    In this article we will look at the next four steps.

    Step 4: Gather evidence
    It is easy to overlook this step as many technicians think of it as the overall ‘diagnosis.’ However, once the technician understands the system, gathering evidence will provide key information. This step is normally best carried out with the use of test equipment that does not mean the dismantling of systems and components.

    Many technicians have their own favourite tools and equipment but this list can include (but not limited to)
    the following:
    Scan tool – It is always best practice to record the fault codes present, erase the codes, and then recheck. This means codes which reappear are still current. Remember that a fault code will only indicate a fault with a circuit or its function. It is not always the component listed in the fault code that is at fault

    Oscilloscope – An oscilloscope can be used for a multitude of testing/initial measuring without being intrusive. Some oscilloscope equipment suppliers are looking at systems within high voltages hybrid/electric vehicle technology. The waveforms produced by the test equipment can be used when analysing the evidence and may indicate that a fault exists within a system. An understanding of the system being tested will be necessary to understand the information. This may even include performing sums so all those missed maths lessons at school may come back to haunt you. It may take time to become confident analysing the waveforms, so be patient

    Temperature measuring equipment – This can include the use of thermal imaging cameras. Most systems that produce energy/work will also produce some heat. The temperatures produced vary from system to system. Examples include everything from engine misfires to electrical components, as well as air conditioning system components and mechanical components such as brake and hub assemblies. The possibilities are endless and results can be thought provoking.

    Emission equipment – By measuring the end result, an exhaust gas analyser can show you if the engine is functioning correctly. The incorrect emissions emitted from the exhaust help indicate a system fault or a mechanical fault with the engine

    Technical service bulletins – Many vehicle manufacturers produce technical service bulletins (TSBs) that are generated by a central point (usually a technical department) from the information that is gathered from their network of dealers. Some of these may be available to the independent sector either through the VM or through a third party – It’s always worth checking if these exist. They may indicate a common fault that has been reported similar to that the technician is facing. Some test equipment suppliers may provide TSBs as part of a diagnostic tool package

    Software updates – Many vehicle systems are controlled by a ECU. Most vehicle manufacturers are constantly updating system software to overcome various faults/  customer concerns. Simply by updating the software can fix the vehicles problem without any other intervention of repairing a possible fault. This is where having a link to a vehicle manufacturer is vital in repairing the vehicle

    Hints & tips – Most technicians will have a link or access to a vehicle repair forum where they can ask various questions on vehicle faults and may get some indication of which system components are likely to cause a vehicle fault

    Functional checks – Vehicle systems are interlinked and typically share information using a vehicle network. The fault may cause another system to function incorrectly, so it is vitally important that the technician carries out a functional check to see if the reported fault has an effect on another system. By carrying out this check the technician again is building the big picture

    Actuator checks – Most systems today are capable of performing actuator tests. The technician can perform various checks to components to check its operation and if the system ECU can control the component, often reducing the time to the diagnosis, by performing this task the technician can identify whether it is the control signal, wiring or component or it is sensor wiring. This function can be used in conjunction with serial data to see how the system reacts as the component functions

    Serial (live) data – The technician can typically review a vehicle system serial data through a scan tool. Having live data readings to refer to can help you review the data captured. Using actuator checks and viewing the serial data can also help the technician to identify a system fault

    Remember to record all the evidence gathered so it can be analysed during the next step in the diagnosis. We can’t remember everything. If the technician needs to contact a technical helpline they will ask for the actual readings obtained recoding the data gathered will help.

    Step 5: Analyse the evidence
    Analysing evidence gathered during the previous steps can take time. The technician needs to build the big picture from all the evidence gathered during the first few steps. You need to analyse the information gathered, and decide on what information is right and wrong.

    This step may rely on experience as well as knowledge on the product. You should take your time – don’t be hurried. Time spent in the thinking stages of the diagnosis can save time later. Putting pressure on the technician can lead to errors being made. It may be necessary to ask the opinion of other technicians. If the evidence is documented it may be easier to analyse or share between others.

    Step 6: Plan the test routine
    After analysing the evidence gathered it’s now time to start to ‘plan’ the best way to approach to the task or tasks in hand.

    The technician should plan their test routine, decide on what test equipment should they use, what results are they expecting, if the result is good or bad  and which component should they test next.

    Document the plan – this enables you to review decisions made at this stage in the next step. The technician may not always get it right as there may be various routes to test systems/components. The test routine may have to be revisited depending on the results gathered during testing. Documenting the test routine will provide a map.  Also, don’t forget to list the stages, as this is something that could be incorporated into an invoicing structure later.

    The technician should indicate on the routine what readings they expect when they carry out the system testing. This can be generated by their own knowledge/skill or the expected readings may come from vehicle information which they have already sourced. If the information is not known at the time the test routine is planned, then the test routine may highlight what information is required and what test equipment is needed. You shouldn’t be afraid to revisit the plan at any time and ask further questions on which direction the tests should take. If the plan is well documented and the technician becomes stuck at any point, they can pause the process and revisit later. Also the information can then be shared with various helplines that support workshop networks.

    Step 7: System testing
    The technician then follows their pre-determined plan, if it is documented they can record the results of the test(s) as they follow the routine.

    Many technicians tend to go a little off-piste when they get frustrated. Having the routine documented can keep the technician on track and focused on the result. If the routine is followed and the fault cannot be found the technician may have to go back to the analysing the evidence or planning the test routine. The technician shouldn’t be scared of going back a few steps, as I said previously analysing the evidence takes practice and can be time consuming, not to be rushed.
        
    Summing up
    Remember to follow the process. It is easy to be led off track by various distractions but don’t try to short circuit the process. Some steps may take longer than first thought to accomplish than others. Some distractions may be outside of your control, and it may be necessary to educate others. Practice, practice, practice. Refine the process to fit in with your business and its practices, the business could align its estimating/cost modelling to the process, being able to charge effectively and keeping the customer informed at each stage of the process.

    Coming up...
    In the next article I will be looking at the next four steps which are; Step 8: Conclusion (the root cause), Step 9: Rectify the fault and Step 10: Recheck the system(s). The last article in this series will indicate the final three steps and how to fit them all together in order to become a great technician and perhaps succeed in Top Technician or Top Garage in 2018.




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