Reasoning and diagnostics Part II

In this issue, Barney Donohew explores critical thinking

Published:  13 March, 2017

We began this journey last issue, so to recap: We need solid reasoning skills to carry out effective diagnostics; persistently good decision making doesn't happen by chance. Possibly out of convenience these skills are often underestimated and undervalued by people, both in and out of the trade. We must raise awareness of the discipline and precision of thought necessary for logical and critical thinking: so we can be better rewarded for our efforts; and to make sure they are consistently and properly applied.

Reasoning, arguments and hypotheses
We covered some fundamentals in my last article: we explain our reasoning using arguments, which contain statements supporting a conclusion; one type of argument, a deductive argument, should guarantee the truth of its conclusion (if it is sound); however, we need to use critical-thinking to check this, by making sure i) there are no other possible conclusions (which makes it a valid argument) and ii) the supporting statements are true.

Within our workshops we constantly face plausible but invalid deductive arguments where the initial statements are true but the conclusion is not guaranteed:

1) The vehicle has faults. Vehicle faults cause DTCs. So, the vehicle has DTCs
2) The vehicle has no DTCs. Vehicle faults cause DTCs. So, the vehicle has no faults

Most of us are wise to the unsound conclusions in these examples, although we have not always been and certainly many of our customers are not.

In diagnostics, deductive arguments are best used when we need to totally justify a conclusion after evaluating a specific system or component test result (e.g. A volt drop above 250mV between these two points on this wire indicates a high resistance fault. The Volt drop is 3 Volts. Therefore, the wire has a high resistance fault between these points.)

How do we justify which test to perform next? We do that by first predicting (making a hypothesis) where the fault might lie by using the observations made within our case (e.g. the symptoms, DTCs and test conclusions). We do not know for sure what the fault might be for any given set of observations (otherwise we would not need diagnostic testing!), so we must make an educated guess as to the probable or possible causes. In these cases, we must use inductive or abductive arguments.

Induction
Imagine a vehicle reporting a P0671 DTC (Cylinder no. 1 glow plug circuit) within the engine ECU. There are no other discernible symptoms. Where should we start our diagnostic process and how would we justify it?

Very likely we would decide to test the glow-plug supply voltage and current draw, as our experience tells us that when there is only one glow plug DTC then it is likely that the glow plug itself has gone open circuit. This is an inductive argument; written formally it becomes:

Almost every time I have read just one glow-plug DTC from an engine ECU (specifically either P0671, P0672, P0673 or P0674), the glow plug within the indicated cylinder has been open circuit. This engine ECU is reporting a P0671 DTC. Therefore, the glow plug in cylinder no. 1 is open circuit.

From our prior knowledge, we have extrapolated a conclusion predicting the probable cause of an observed DTC; i.e. we have hypothesised a likely fault within a candidate component. From a perspective of critical-thinking we must bear in mind that the conclusion is not guaranteed to be true. This is a feature of all inductive arguments and we can only assess them relative to the strength of their arguments. Diagnostically, we might use our critical-thinking to weigh-up whether the strength of an inductive argument (amongst other factors) justifies us carrying out a system or component test, but it is unwise to rely on it to entirely accept or reject any hypothesis about what is the fault. The glow-plug example could be classed as a mildly strong argument. A stronger inductive argument might be:

Every time I disconnect a CKP sensor on a running vehicle the engine stops. Therefore, if I disconnect the CKP on this vehicle the engine will stop. [I have yet to come across a vehicle where this has not been the case but there remains the (admittedly very slim) possibility that an engine on some vehicle somewhere in the world at some point in time might continue running with its crank position sensor disconnected].

Essentially the inductive arguments above describe case-based reasoning: "This set of symptoms is like those I observed in a previous case. By analogy, the fault might be caused by..." However, experience can be a double-edged sword: we must be flexible in our reasoning and able to revise our beliefs if necessary; especially in the face of rapidly evolving automotive technology, where any given symptom might be caused by an increasing myriad of potential faults.

Abduction
Even the most knowledgeable amongst us face situations in which they have only limited experience, understanding or exposure; whether that pertains to an entire system, subsystem or the outset of a case displaying a sparse set of symptoms not previously encountered. It happens to all of us. Regularly. So, if, for example, we find ourselves with a vehicle exhibiting some odd, never seen before, behaviour, what is it we do (after checking all the basics, of course) that gets us to the point of selecting a given system or component test?

Well, we might use parts darts or a brute-force attack (sequentially testing each component one by one) or perhaps something better?! How about if we use theories (hypotheses) that relate component faults to possible symptoms and find the best match of these to the set of observed symptoms to try to predict the likely cause of the problem? If this happens to be what you do, then you are doing the right thing; it is a creative hypothesis forming process known as abductive reasoning and is the most skilful and challenging part of diagnostics. Although it is often summarised as "forming your best guess" it is the only diagnostic strategy that, with practice and knowledge, will allow you to complete the diagnostic process efficiently and effectively.

The hypotheses we form must fit within all existing knowledge regarding system and component behaviour and explain the causes of any possible sparse and/or diverse set of observed symptoms, as well as any new observation added to that set (otherwise a new hypothesis will be required).

Think back to the first time you encountered a P0171 DTC (system too lean), still a (infamously) problematic scenario for many. It is the perfect scenario for an abductive approach: for this symptom, we must consider a set of possible faults and their side-effects, e.g. what faults might cause the engine to sense more air than it is expecting (i.e. air intake leak downstream of air-mass meter; under-reading air mass-meter; faulty oxygen sensor; faulty throttle position actuator or sensor etc.) and relate them to the observed DTC and any other symptoms (e.g. erratic engine idle). Each possible candidate system or component will have its own chance of being the actual fault and we must proceed with our diagnostic testing and systematically prove (using deductive evaluation of system and component test results) where it lies.

Messing with memes
Over the last couple of years, a meme has entered the consciousness of many technicians and readers of Aftermarket Magazine: #testnotguess. Whilst appropriate, with our new knowledge, we see that it could be replaced with an alternative meme to more accurately convey the entire diagnostic process and provide positive instruction: #guessthentest. Given that we must use our imagination to create a hypothesis (which we must test), our imagination is a valuable tool within our diagnostic arsenal (and must be recognised as such); if we view guessing as either an act of induction from our prior knowledge or, the more creative, process of abduction, then the meme neatly encapsulates fault-finding.

Summing up
We can use inductive arguments to justify, with some probability, which potential fault might cause any observed set of symptoms based on our past experiences or knowledge.

We use abductive reasoning when we need to predict a set of symptoms, from their hypothesised relationships to possible component faults, that best match (or cover) an observed set of symptoms. Neither reasoning method guarantees the truth of their conclusions and must be validated.

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  • Scrappage: scrap the negativity? 

    With new car sales on the slide during 2017, vehicle manufacturers delved into their big ideas bag and pulled out a classic from the turn of the decade: Scrappage. At the last count, 17 carmakers  including, Volkswagen, Skoda, SEAT, Audi, Ford, Mazda Renault , Hyundai and Toyota had set up schemes. Money on the table varies, but some are offering motorists up to £8,000.

    While these are all manufacturer schemes with no government backing, they bring back memories of 2009-2010 when the official programme was offering motorists £2,000 to scrap their old banger. Many in the aftermarket were pulling their hair out at the thought of customers scrapping perfectly sound older cars to get a discount on a brand new vehicle that would probably not see the inside of an independent garage for some years.     

    The freedoms of Block Exemption and the overall business acumen of the aftermarket may have mitigated the damage a few years ago, but now it’s back on the agenda. There are even suggestions that government might consider another official scheme to accelerate the exit of diesel vehicles from our roads. You know, those diesel vehicles that a previous government encouraged in the first place?

    Talk about dirty politics.

    Anyway, while the manufacturer schemes mostly expire by the end of the year, should we be concerned about the return of scrappage?

    Impact
    Wendy Williamson, CEO at the Independent Automotive Aftermarket Federation (IAAF) is not a fan: “In general, vehicle scrappage schemes can – and do – negatively impact the aftermarket long-term. An example of this is the 2009 scrappage scheme which removed up to 400,000 serviceable vehicles from the aftermarket and did little to support UK jobs, as most vehicles acquired under the scheme were from non-UK factories. Through offering consumers an incentive, scrappage schemes may be seen as a cynical ploy to increase new sales. And herein lies a major problem, as we’re not just talking about off-road cars consigned to the scrapheap that were due their MOT or service, or requiring replacement parts. While the independent automotive aftermarket is very adept at servicing newer vehicles, much of the servicing and repair of new, zero to three year old vehicles is with the main dealer.

    “New vehicle sales are declining, hardly surprising given the highs reached in recent months and years but, the repercussions for the aftermarket could be far worse with new vehicles flooding the market thanks to scrappage schemes.”

    Legislative loophole
    One obstacle of a potential newer vehicle parc for the aftermarket is the forthcoming Type Approval legislation. This relates to the diagnostics, repair and maintenance of vehicles and are an important step towards improving the legislative framework for independent operators. Over 184 amendments were approved and importantly for the aftermarket included a number of key revisions, the most important of which is keeping the OBD port to the vehicle open and accessible.

    Wendy has serious concerns here: “There is a risk that some of the vehicle manufacturers would use a legislative loophole to replace the OBD connector with another system in new models of cars, potentially gaining a monopoly on access to vehicle technical condition data.

    “A new vehicle parc makes this more feasible and also raises the question of data access.  If we get the access rights that we should enjoy under current legislation then providing the workshop has the right tools and equipment they should be on a level playing field with the franchised sector.

    “However, the information the aftermarket currently receives in not at the same detailed level as the dealer network and this is

    For Wendy, the larger issue is not scrappage, it’s what’s coming down the line behind newer cars: “The big threat at the moment is that through ‘the extended vehicle’ the aftermarket will no longer be able to enjoy unmonitored access to the vehicle information.”

    Minimal
    Opinions on scrappage vary however. While scrappage takes vehicles out of the car parc,  more are always coming in. Terry Gibson, head of member services at the Independent Garage Association (IGA) feels scrappage is not a big concern, or even that relevant to the sector: “So called ‘scrappage’ schemes are good for car sales – period. The last time there was a genuine
    So, garages are not losing business, and hopefully not losing sleep either. After all, from a legislative and a practical standpoint, today’s independent aftermarket is a much more sophisticated place – they can handle more modern vehicles in larger numbers – why not let them come?  “Exactly,” replies Terry. “Modern independent garages invest heavily in tools, technology and training to keep pace with changes in vehicle technology. We say – bring it on.”

    Of course, legislation can change, and you sometimes take your life in your hands when you trust it to committee. Brexit could have an impact on the Block Exemption Regulation (BER) and Type Approval might not go ‘our’ way. Could independents lose the right to service new vehicles without invalidating the warranty?

    Terry has a positive view: “While there is no certainty in this area – and a certain amount of noise in some quarters, the high volume of European cars sold in the UK suggests that it is unlikely that we will see any wholesale change in the right to repair arena.”

    Assuming the schemes all succeeded, a surge of new cars coming into the parc could speed up some of the more worrying trends, like connected car. However, the industry is resilient says Terry: “Although it’s true that some of issues around connected cars may present challenges for independents, the inevitable outcome of an increase in challenge is an increase in solutions – driven by the efforts of trade bodies like the IGA.”

    It’s not a simple picture is it?  “Very little is simple these days,” adds Terry, but one thing is for sure, independents will never lose customers if they continue to focus on the personal service and honest communication that creates the lasting customer relationships that are the hallmark of independents’.”

    For industry consultant Andy Savva, scrappage is a non issue: “I don’t worry about scrappage. As far as I am concerned it is a marketing ploy to pull forward sales. Then again, I was never concerned about my business being damaged by older cars being superseded by newer models.”

    Andy’s concern is more about business planning in the aftermarket: “Concerns about scrappage are really come down to fears about change and the ability to plan ahead. Unfortunately, many businesses in our industry don’t do so well in this area.”

    Andy believes businesses have all the information they need to work forward and invest, if they look at the sales going on at any given moment: “When I was running my garage, I focused on the three popular brands in my area. I would look at the sales figures and know that cars from those brands were going to be coming through my doors for the next three or four years.”

    Planning
    Knowing what to do is one thing, applying that knowledge is another though: “In the aftermarket, most garage owners don’t plan ahead. The average mainstream garage might be looking a few days ahead, or a couple of months at best, but not much further than that. It is one of the problems we face as an industry.”

    For those who are looking forward, there is a bright side to this, although it’s a little hard on those who don’t: “Within five to seven years, a third of the garages currently in trade won’t be in trade, which means there will be more business for those who are looking forward.

    “It’s not just independents who struggle remember – if franchised dealers need scrappage to sell cars, what does that say about their ability to cope?”

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