September 2019

BY John Batten P icture this: You’ve a mildly grumpy client stood at your front desk. We’ll call him Mr Brown. He has been a happy customer for many years, you’ve serviced his vehicles regularly and all has been good in the world. Unfortunately, today is Mr Brown’s third visit to your counter for the same problem. He’s understandably becoming irritated by the fact that your technicians aren’t able to identify the reason behind the intermittent loss of power with his VW Golf, and he’s starting to doubt the competency of your business. It’s a common problem, so your garage should have a robust solution. If not, then you could lose Mr Brown's custom. See this happen too often and it will put a major dent in your bottom line. Nobody wants that. Is there a solution to the intermittent fault dilemma? In many instances yes. You just need to apply the right routine. With the right routine, tools and information you’ll dramatically increase your chances of finding the fault in the first go. Apart from keeping Mr Brown happy, your techs will enjoy the buzz of early diagnostic success. The big question is what needs to change in your garage to improve your chances of nailing these elusive faults? A look at Mr Brown’s vehicle will show a pattern that you can use in your garage. Mr Brown’s Golf has been experiencing a sudden loss of power. It makes him pull over to the kerb. Stopping and starting can make the problem disappear and not occur again the same day. The vehicle has been scanned and road-tested on both visits. A fault code relating to rail pressure deviation has been recovered in both instances, but no fault was found on the multiple road tests completed. What can you do to get to the root cause of this problematic situation? Just use this routine: 1: Thorough grilling at front desk We find the following statement usually has a client bending over backwards to help: “Sir – It would be great to speak, if you have a few minutes, so that I can find out some specific details of the fault on your vehicle. We often find that a few minutes of your time now will often help us find the issue and could save you money on the cost of your diagnostic evaluation.” All you have to do now is ask the right questions to ascertain a point at which something changes on the vehicle and the details around that, as well as some specifics as to when the fault occurs. In this instance further questioning revealed that the problem normally occurs around a mile or so from Mr Brown’s home, after he’s started his journey in the morning and occasionally on his way home. Armed with this information, you give Mr Brown a courtesy vehicle so that you can carry out the tests the next day. 2: Where did I put that silver bullet? We’re already one step closer compared with previous visits, and have a constantly recurring fault code for high-pressure control deviation. Initially, it’s worth making this the focus of our diagnosis. For starters you could take a look in ELSA (where the VAG group keep their silver bullets) for any known issues in their service bulletin archives. You find one relating to a known mechanical fault for the high-pressure pump wear resulting in constantly low pressure, but nothing for an intermittent fault such as yours. To be on the safe side you inspect the known issues and find the connection between the camshaft and the high- pressure pump to be in good order. 3: Desk diagnostics -Where the magic happens It’s in stage 3 where the magic begins. You need to make an exhaustive list of the reasons that could raise this fault code: A Restricted supply to in-tank pump B Faulty in-tank pump C Power/ground supply fault to pump D Faulty low-pressure fuel pump control module E Restriction between the low- pressure and high-pressure pump F Faulty high-pressure pump G Faulty high-pressure control valve H Power/ground supply fault to high- pressure control valve I Faulty high-pressure sensor J Faulty wiring to the high-pressure sensor K Faulty injector/s L ECU power or grounds M ECU software N ECU hardware One fault with 14 possible causes? There’s only one thing for it: 4: Testing, testing, testing - It’s all about priorities There’s a straightforward reason why this vehicle hasn’t been diagnosed on the earlier visits. Quite simply, the 22 AFTERMARKET SEPTEMBER 2019 TECHNICAL www.aftermarketonline.net INTERMITTEN FAULT DIAGNOSIS: IN 5 STEPS Intermittent faults are the bane of our lives. Use these five steps to dramatically improve your chances of a first-time fix