Is it there or not?
How long does it truly take to find an intermittent fault, and how do you manage to isolate it?
Published: 26 January, 2023
Intermittent faults are always the most difficult to find. Therefore, when I was tasked with attempting to diagnose and rectify an intermittent cutting-out fault I knew it would not be straightforward.
The customer had heard of me via my social media page and local garages who use me for their diagnostic work. The customer complained that the vehicle, a Renault Traffic 2.0L TDI, would stall on its own, intermittently. The vehicle would then start up again as soon as the ignition switch had been cycled. This fault could occur within the hour or take five hours before it would surface again. The customer advised there was no rhythm or rhyme to the fault, and it could occur at any time. Knowing this would be a very time-consuming fault I advised the customer I would need the vehicle for a week to ensure experiencing the fault and carrying out testing thoroughly. The customer was more than happy to oblige, as long as I fixed the fault, so no-pressure then…
Initial approach
I started by carrying out a full system scan of all the vehicle’s computers. I found in the engine control module a fault code for ‘Computer internal electronic fault.’ Please refer to Fig.1. This was a good starting point as this fault code is very specific and often is caused by an internal control module error, wiring fault to the computer or a component directly related to the computer. However, at the cost of a new engine computer (over £1,200) I needed to pinpoint the fault and not rely solely on the fault code provided. I cleared all the fault codes present in the engine ECU and ran the vehicle in the workshop until it cut out. Once the vehicle cut out, I re-read all the fault codes and the only code which returned was the internal electronic fault as described earlier.
I noticed that when the vehicle had stalled, communication was still present and live data parameters were still being displayed by the scan tool. This indicated the engine computer is alive and operating. This was a good indicator that the engine computer is receiving the voltage and ground supply. Without it, communication would not be possible. I needed to confirm this for certain as I cannot diagnose a fault solely on suspicion.
To access the engine ECU on this vehicle I needed to remove the bumper, headlight, and security cage around the engine ECU. Before I attempted to remove all those components, as this was very time-consuming, I wanted to use an oscilloscope to check the fuses that feed the engine ECU at the time of the stall. These fuses are on the output stage of the engine control relay, therefore if it was the relay that was failing, for whatever reason, I would see the drop-out on the oscilloscope. As you can see from Fig.2, the supplied voltage and ground were constant and did not drop-out. This indicated that the engine control relay was latched and doing its job properly when the fault was present. I now had no choice but to access the engine computer to carry out further testing.
By removing the bumper, headlight, and security cage I was able to access the engine computer and its respective wiring harness. Concerned still of a voltage or ground supply issue, I connected the oscilloscope to the engine computer supplies and verified, during the stall, that these were present. Next, I wanted to verify the main inputs and outputs of the computer that could contribute to a stalling condition. I connected to the camshaft and crankshaft position sensor wiring, directly at the engine computer. I also connected to the injector wire using an amp clamp to determine if injector operation remained constant during the stall event. If not, I could then determine if injector pulse ceased due to a loss of a cam or crank sensor signal.
As you can see from Fig.3, the cam and crank sensor signals remained and the injector control was the first to be lost, thus resulting in a stall of the engine. The engine computer was no longer providing injector control to keep the engine running. Since proper cam position signal remained during the stall it was unlikely to be a 5v reference fault, as the 5v reference is used to power the camshaft sensor. At this point, from the evidence I had retrieved coupled with the fault code I initially found, I was highly suspicious of an internal engine computer fault.
There are no problems, only solutions
Due to the current issues surrounding the supply of electronic parts in the UK I was not able to obtain an engine control module directly from the dealership. I had only one option which was to locate a used control unit and carry out cloning of the original control module.
This process requires removal of the engine computer from the vehicle and connecting a programmer directly to the ECU. Please refer to Fig.4. You are then required to read the flash and the EEPROM internal to the computer and transfer that data from the suspect's faulty original ECU into the donor ECU. Please refer to Fig.5 and Fig.6.
By going through this process, you are effectively making an exact copy of the original ECU, allowing all the immobiliser and coding data to be transferred so you can simply connect the ECU back to the vehicle without any further programming being required. This will only rectify a hardware-related fault. If there was a software-related issue, then you will effectively copy the fault onto the donor unit. I was confident this was a hardware-related issue rather than a software-related problem. Once I had cloned the ECU, I left the engine idling to attempt to re-create the original complaint. I can confirm the donor ECU I cloned had fixed this intermittent fault as the stalling no longer occurred.
With intermittent faults, the best way to tackle them is to gather as much data as you possibly can, performing as little work as possible. This will then stop the hours and hours of stripping parts off needlessly to carry out inspections that are not required. A solid foundational knowledge of how systems operate on today's complex vehicles also provides a strong advantage. Logic can then be used to narrow down the possibilities that could cause the fault as we have done in this diagnosis and repair.
- Non-intrusive testing
As technicians we’re all expected to be able to diagnose a fault within a sensible timescale, for a reasonable price, then guarantee the fix. With correct training, information and tools this is possible. However, we are often faced with multiple faults where cause and effect may not always be straightforward. We can be in a situation where we need to rectify faults before we can move on to the next. Also, if the repair cost could outweigh the vehicle’s value or customer budget then great care must be taken explaining the situation, agreeing a starting fee and preparing and executing a successful diagnostic plan.
Recently we were presented with a BMW X3 for poor performance and a suspected DPF fault. After interrogating the customer we gathered all necessary information. Initial diagnosis confirmed multiple fault codes and a blocked DPF. Determining what caused the DPF to block is vital for the correct diagnosis and preventing reoccurrence. We created a test plan to test each fault and separated them into faults that affect the performance, faults that can cause the DPF to block or prevent regeneration and ones that don’t. In order to fully test the vehicle we would need to clean the DPF first as the exhaust back pressure was so high, the vehicle was barely drivable. As a member of the DPF Doctor network we have a very successful method of cleaning the soot from the DPF without the need for removal and access to many manufacturer-specific tips with DPF faults. The information and knowledge within the DPF Doctor network has proved to be invaluable and has given us an outstanding success rate. With our test plan ready we were able to calculate a sensible labour figure to conduct the tests required. The customer authorised the labour and the DPF clean.
Several faults were straightforward. A multimeter gave us conclusive results and made it easy to quote for replacement parts and labour time to fit them. The main fault causing poor performance required a little more thought to keep diagnosis time to a minimum. A low boost pressure fault code doesn’t tell us why the pressure is low. Driving the vehicle whilst monitoring the boost pressure showed the fault was intermittent, so an external boost leak was unlikely. A smoke test was also carried out which revealed no leaks. In this instance, the EGR valve could be a likely culprit. This engine uses a vacuum controlled EGR valve with a position sensor built into the diaphragm. As tempting as it was to unbolt it and take a look, this would all take more time then factor in the risk of rusted bolts etc. With a position sensor one would think if the valve was to stick then a fault code would be set. We had to plan a simple, conclusive, yet non-intrusive way of testing the EGR system quickly.
The conventional vacuum controlled EGR system consists of the EGR valve which includes the diaphragm with a 5 Volt position sensor and the vacuum control solenoid valve which uses vacuum from the brake servo vacuum pump and is controlled by the ECU on a duty cycle. The position sensor will typically show 0.5 to 1.2 Volts when fully closed and 3.9 to 4.5 Volts when fully open. One side of the solenoid valve has a 12 Volt (battery Voltage) supply and the ECU switches the ground path on and off at varying duties to vary the vacuum amount thus varying the EGR valve position. The ECU looks at the position of the valve and adjusts the duty to achieve the position desired similar to how an ECU uses the oxygen sensor to adjust the air/fuel ratio. With the following tests we were able to check every component in the system.
Test one
We connected the Mityvac directly to the EGR valve and the oscilloscope connected between the signal wire and battery ground. As we had already smoke tested the entire inlet system we connected the smoke machine directly to the inlet manifold in place of the intercooler hose. With the smoke machine running and the ignition on (engine off) we used the Mityvac to fully the valve to check it had no vacuum leaks (split diaphragm), then we opened and closed the valve slowly and then quickly. This confirmed the following:
- Hide and seek
By Ryan Colley, Elite Automotive Diagnostics
- Reasoning and diagnostics Part II
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.
- The shape of things to come
Engine and exhaust management can be a formidable task, including working through multiple symptomatic issues to finally reveal the heart of the fault. This can include sensor diagnosis and fitment as part of a high-quality repair. Such a small thing as sensors can make a huge difference to the dark art of emissions management.
The increasing desire for emissions compliance for more than just an annual roadworthiness test is pulling focus on the workshop’s emission management know-how. For instance, it matters when it comes to selling the vehicle, and quite rightly vehicle owners will feel very strongly about looking after one of the bigger investment pieces in their life. It is also a viable eco-friendly strategy to keep existing vehicles on the road for longer and maintaining them to optimum emissions standards.
It’s reassuring for garage customers to have their technicians well informed about exhaust management, as often the workshop needs to enter into a teammate type working relationship with the vehicle owner, including agreeing investigation time and even exploring DPF-saving strategies together. Technician confidence about where to start and why paves the way to a smooth customer service experience.
The serious business of tackling exhaust management is the shape of things to come for the NTK portfolio. A new group of exhaust pressure sensors will be rounding out NTK’s engine management offering, including exhaust pressure sensors (EPS), differential pressure sensors (DPS) and high-pressure sensors (HPS). The new exhaust sensors make the perfect accompaniment to the existing exhaust offering making the NTK portfolio a go-to solution for technician confidence in the parts selected.
So why does starting small matter? Firstly, it could prevent jumping to worst case, and expensive-case, scenarios which can be quite a pain point for the vehicle owner and hard for them to understand the technical rationale behind the work. Starting with sensors can empower much needed accurate diagnostics, as well as optimum on-board management for the driver. A high performing sensor like those in the NTK range can also help prevent additional damage to related components like turbos and filters through fast and reliable measurement. Finally, sometimes it can be the required repair itself, cutting through the uncertainty from a mix of fault symptoms.
Becca Knight, Marketing Manager for Niterra UK commented: “Exhaust management is no longer the reserve of a specialist garage- all workshops need to be prepared to tackle emissions as part of their core service offering. The sensors currently in our portfolio, and the new range coming by the end of 2023, furnishes workshops with market-leading precision and performance so they can offer the best repairs for their customers.”
Also available from Niterra UK is the online Training Academy, helping technicians upskill and up-confidence in exhaust and engine sensors, standard servicing, hybrid technology, and so much more at ngkacademy.com. Starting small with the skills and the knowledge is one of the best ways to tackle emissions-readiness head on and to show your customer’s that they and their vehicle are in safe hands.
For more information about Niterra UK and its products and services, visit: www.ngkntk.com/uk
- It’s Evoque-ative
I was recently tasked with looking at a vehicle which had the dreaded 500-miles-or-less-until-the-vehicle-cannot-be-started warning on the dash display. We have all been there before with this sort of issue. This is a typical warning you will see on vehicles fitted with an AdBlue emission system if there is a fault present. The vehicle in question was a Range Rover Evoque 2016 2.0TDI.
The customer who brought the vehicle to me was a trade customer. They advised that the vehicle originally came into them for repair for an engine warning light which intermittently illuminated. The fault code was for Nitrogen Oxide (NOX) sensor 2 no signal. I started by carrying out a full system scan of the vehicle as I would routinely do. The result was multiple fault codes stored in the engine management system control module relating to the AdBlue system. Due to having so many codes stored, I checked all the relevant freeze frame data for each code and then erased them. Following this, I attempted to carry out a road test, but a fault code returned almost immediately for no communication present with NOX Sensor B.
Signal and communication
Armed with this information, I thought it would be a fairly straightforward diagnosis. However, I was wrong. It never goes the way you would like it to, especially at the end of the day. I put the vehicle on the ramp and obtained a wiring diagram to check the wiring directly at the NOX sensor. Upon first inspection, it was clear the sensor had already been replaced. I contacted the customer, and they confirmed the sensor was indeed both new and genuine from the manufacturer. I then checked the wiring to the sensor. These types of sensors are fairly straightforward to check because they have only four wires which have signals on. These are power, ground and CAN bus communication. I firstly checked the power and ground and confirmed these matched the genuine wiring schematic. Please refer to Fig.1. Next, I then connected an oscilloscope to the circuit to monitor the CAN bus signal. I found the CAN bus was shorted to each other and what would appear to be 12v. Please refer to Fig.2. The simplest next test was to unplug the sensor and to monitor the CAN bus signal. I found with the sensor unplugged the short was no longer present and the CAN bus signal returned, which would mean that the sensor was faulty wouldn’t it? Please refer to Fig.3.
Slightly concerned I was missing something as the sensor had already been replaced, I decided to contact Neil Currie. As well as being the winner of Top Technician 2019, he is a contributor to this very magazine and a Land Rover/Range Rover guru to boot. He advised me that if the sensor has been replaced and it is a genuine sensor provided by Range Rover, then the pin configuration has been changed and you are required to move the pins around in the connecting plug in order for the new sensor to operate. This has been done due to a change in manufacturer used by Range Rover to produce this style sensor because of a lack of available original manufacturer NOX sensors. The details can be found here from a bulletin released by JLR.
Full system scan
After de-pinning the connector and swapping around pin 2 (CAN) and pin 4 (Ground), I rechecked the CAN bus signal and found the signal is now correct and is no longer shorted. Please refer to Fig.4. After carrying out a full system scan, clearing and resetting the AdBlue counter, I now found that the warning for 500-miles-remaining had, vanished and there were no fault codes returning. This vehicle was now fixed.
I thought this was a very interesting case study as both the aftermarket and genuine diagrams both show the original wiring of the NOX sensor and there is no reference to a modification, unless you are aware of this issue or have access to Range Rover’s technical service bulletins this would certainly take you up the diagnostic garden path. Luckily for me, networking with the finest technicians in the country is a great way to stay up to date with these types of modifications.
