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
Published: 25 September, 2019
Picture 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 right tests have not been completed at the right time. That’s all about to change.
You need to decide how best to test the possibilities. This is how I would prioritise:
A Fit fuel flow tester in low-pressure supply
B Scope CH1 WPS 500x pressure transducer pre-fuel filter
D Scope CH2 WPS 500x pressure transducer post-fuel filter
C Scope CH3 in tank pump 20Khz PWM positive supply from low pressure pump control module
D Scope CH4 ground in tank pump ground
E Scope CH5 in tank pump current
F Scope CH6 high-pressure rail sensor signal
G Scope CH7 high-pressure control valve +
H Scope CH8 high-pressure control valve –
The objective is to carry out as many tests as possible in unison. I’ll also be able to road test the vehicle and stand a VERY good chance of diagnosing this problem the first time the fault rears its head.
5: Diagnostic sniper
Diagnosis is all about ruling out what’s good. Do that methodically and the problem will reveal itself like an enormous arrow descending from the sky: “THE FAULT IS HERE.” This is exactly what will happen when you road test this Golf.
You’ve set up your tests and set off on your test drive, complete with assistant. You’ve been driving for around 10 minutes and just as Mr Brown predicted the vehicle loses power and you’re forced to pull over. This is great news. Let’s take a look at the clues:
- Fuel flow dropped dramatically as vehicle lost power
- Rail pressure dropped at same time
- Powertrain ECU increased duty cycle of the high-pressure control valve
The results pose the question “is the low pressure supply good?”
Let’s take a look.
- Fuel pressure pre-filter reduce
- Fuel pressure post-filter reduced
- Duty cycle to low-pressure pump increased
- Power supply and grounds to low-pressure pump remained good
- Fuel pump current increased
It’s great to see the pieces of our diagnostic puzzle falling into place. The drop in pressure, and the fact that the powertrain ECU has increased duty to command more fuel clearly indicates the ECU is trying to rectify the drought, but what’s causing this?
The devil is in the detail here and the final clue is in the fuel pump current.
There are very few causes for low-pressure fuel pump current increasing while post-pump pressure reduces. The most obvious would be fuel pump speed reducing due to pump failure. That’s exactly the fault with Mr Brown’s Golf. Bingo! you’ve found it!
This five-step system is straightforward and greater than the sum of its parts when executed thoroughly. Miss any individual step though, and you might not be seeing Mr Brown back in at your garage.
- CAN I FIX IT? Yes, I can!
By Neil Currie
- Tyre Fix
Automotive Brands, parent company of Power Maxed has released Tyre Fix. In the event of a puncture, Tyre Fix can be affixed to the air valve of any flat tyre and entirely injected into the tyre. The vehicle can be driven at 30mph for up to six miles. The packaging does recommend changing the tyre as soon as possible but, like with a spare tyre, it buys the user an extra day peace of mind while the vehicle is booked in to have the tyre professionally repaired or replaced.
www.tyrefixrepair.com
- Hartridge DPF200 Master
Delphi Technologies has launched the Hartridge DPF200 Master. Restoring the DPF if it is malfunctioning will help to improve fuel economy, improves exhaust function and extends the life of the filter. This new addition joins the company’s existing DPF cleaning range. The software built into the machine automatically includes flow testing and ‘failed cell’ detection diagnostic steps so that a faulty filter can be identified prior to cleaning. With a patented bi-directional dry air cleaning process that pulses high volumes of compressed air at both ends of the filter.
www.hartridge.com
- No Smoking!
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).
- Now is the time
COVID-19 has caused a whole slew of scenarios that no one saw coming a year ago. One that was pretty apparent early on in the pandemic though was that many people would be looking to make savings where possible, and the independent garage sector tends to do well when the cost of going to the dealer becomes unsustainable.
Once you have the customers, you need to continue to help them. Just because your labour rates are lower, in some instances the sheer cost of replacing parts will make repairs very expensive. In these instances, remanufactured components may be the answer.
Process
Echoing the previous article in this issue, we start with steering. “Quality is the key word when it comes to steering systems,” said Edin Elezovic, Product Manager for Steering at BORG Automotive, “as the latter ensures that the driver is in control of the vehicle. Customer-perceived quality is exactly what BORG Automotive, the owner of brands such as Elstock, DRI and Re-EX, invests substantial effort, time and resources in achieving. The goal is ultimate quality at least on a par with OE parts. Nothing less.”
Edin continued: “The process of remanufacturing is based on expertise in remanufacturing which stems from many decades in the market. It uses innovative engineering methods devised by the company itself to allow for the most effective process and quality assurance. All the components the organisation remanufactures pass through the same process. They are dismantled, cleaned, inspected and sorted, reconditioned or replaced and reassembled. Finally, each unit is individually tested and subject to a rigorous inspection before being painted and packed to meet customer expectations and requirements.”
Among the different product groups at BORG Automotive, the steering products - racks, pumps and electric columns - are all remanufactured at BORG’s plant in UK, where the steering know-how and expertise is located.
Edin observed: “Regardless of the vehicle segment, BORG remanufactures to the highest standards so the customers can install the products with peace of mind. Only OE cores are remanufactured and all critical components are fully replaced to ensure the highest quality. During the quality check, all cores and parts are visually examined and the tie rods are subject to strict OE standard internal compliance. After dismantling, the parts will undergo the multistage washing process to ensure the cleanliness of all internal and external parts. After assembly, the units are subject to our electronic end-of-line testing using real-world simulation to ensure their functional performance is at OE level.
“BORG Automotive’s steering products have experienced an incredibly high growth rate. Such progression is driven by racks, specifically the hydraulic power family, the volume of which has quintupled in the last five years thanks to BORG Automotive’s structured approach of process development and continuous focus on improving quality, which has now achieved its highest point historically.“
He continued: “We have achieved a level of quality that our customers are very much satisfied with. For instance, we can see that the number of claims we receive is almost four times less compared with two years ago. This level of quality is necessary to satisfy our OEM customers."
Mechatronics
To sustain growth in the long term by confronting the transitions taking place in mechatronics, BORG Automotive’s engineers in UK have focused on implementing processes and testing procedure that enable the remanufacturing of the latest generation of electric power steering racks, even those requiring fault-tolerant and time-deterministic protocols such as FlexRay.
“We believe that electronic steering racks will be the most common type of steering rack in the future,” said Edin “and we actually expect that more than half of the European car parc will be fitted with ESRs in the course of the next 10-15 years. We have therefore made massive investments in our ongoing work with mechatronics, which means that we are prepared with new technologies to expand our product portfolio.”
BORG Automotive is continuously developing its remanufacturing processes and is adding many new products to the existing ranges. It is investing a great deal in exploring new car models in the market and is researching how to remanufacture these parts, which is the key to sustained market coverage. As an example of this, BORG recently released racks for the latest BMW and Ford applications.
“In our newly built mechatronics facility, we created an ESD protected area (EPA). This gives us the opportunity to effectively control and avoid issues caused by electrostatic discharge (ESD), as this can have a damaging effect on components and products containing electronic circuitry. For the new facility we have developed our own electronic testing equipment in order to ensure high-quality products.”
Edin went onto say: “We have expanded our mechatronics team as we are fully aware of the future of mechatronics within the field of steering racks. We have an in-house facility built for this purpose with an ESD-protected production area.”
He added: “Thanks to all this, steering products from BORG Automotive offer quality on a par with OE parts. But it is not just the quality that is extremely important to BORG Automotive; it also wishes to provide the best possible customer experience when it comes to remanufactured automotive parts, which is why the company continues to strive to offer a plug-and-play solution so that the mechanic enjoys an uncomplicated installation experience.”
Additions
Remanufactured component providers are adding more product all the time, across the car. With this in mind, Ivor Searle recently added manual transmissions for the Ford Fiesta, Focus and C-Max to its all-makes range of gearboxes for cars and LCVs. The newly-added applications include units for 1.0 litre petrol EcoBoost derivitives of the Fiesta and Focus, as well as 1.6 litre diesel DuraTorq powered versions of the Focus and
C-Max.
Commenting on the company’s reman programme, David Eszenyi, Commercial Director at Ivor Searle said: “Ivor Searle‘s remanufactured gearbox programme covers around 90% of the UK’s vehicle parc and cost up to 40% less than OE. For peace of mind, all Ivor Searle gearboxes are covered by a 12-month unlimited mileage parts and labour warranty.”
David concluded: ”In addition, Ivor Searle holds comprehensive stocks to ensure first class customer service and minimum vehicle downtime and provides free next day UK mainland delivery for stock items ordered before 3.30pm.”
