Diesel diagnostics for the workshop
Frank examines how following tried and tested diagnostic procedures in a consistent way will enable you to successfully find diesel faults
By Frank Massey |
Published: 11 May, 2020
I’m mindful of several recent diagnostic topics that focused on cutting edge opportunities such as noise and vibration analysis. It also reminded me of the most important aspects of fault finding; to focus on the symptoms, ask relevant questions and conduct a methodical approach based on systems knowledge, accurate data and a proven process.
All of this really boils down to training, experience, and confidence. There are no short cuts, cheap fixes or internet gurus. There are however basic steps that are easily introduced into your workshop procedures.
This brings me to the topic in hand. Can we conduct relativity simple tests on common rail diesel systems? Not only can we, but we must! Remember, the foundation rule of fault finding is a simple methodical approach. Don’t expect a magical fix-all in less than 1,000 words. However, I can provide a pathway that will illustrate the area of responsibility and potential investment in time and money.
Vital information
The first vital step is to listen and ask questions. Owners often have vital information. Remember this is not a recipe for short cuts or silver bullets for your machine gun. Your approach will always depend on the extent of problems. Will it run? are there any mechanical noises? Is there a loss of power? if so when? Is the fault intermittent and how did it start? There is an endless list of questions that will help establish a hidden history.
I often find that a physical examination or health check helps understand the way the vehicle has been driven and serviced. This will often expose basic problems especially with charge pressure circuits.
Try to explore all non-intrusive tests first. They may not be entirely logical in order of priority, but do provide results in the minimum time period. With experience, you will hone these steps into a razor-sharp intuitive process.
Serial investigation
Serial investigation is without doubt the correct first step. Do not jump to premature conclusions as serial data often shows symptoms, not cause. For example, a faulty air mass meter will cause EGR calculation error values, incorrect load and boost calculation. This is a common problem with many causes.
The volumetric efficiency relies on the intake system, swirl flap control, turbo spooling, and a free-flowing exhaust system. Please note that I keep my thoughts non-specific yet focused on all possible causes. This is a very important reaction in any diagnostic process.
Assuming a non-run condition, excluding any serial clues as often there are none, I would always check for the correct rail pressure. This can be done with a DMM. Expect around 1-1.5v with a quick rise time of 0.5-1sec. If it is slow to rise or low, check the priming system including the filter. This should be done with a gauge. Remember pressure, flow and pump current. This will depend on system type so check the schematics carefully. Most systems now prime at 5-6bar.
Isolate components
A slow rise time may be due to an internal leak or worn components within the high-pressure system. This includes the HP pump, rail limit valves, and injectors, as well as volume and pressure regulation devices. Always isolate various components and conduct a blind or proof test before suspecting the pump. They rarely fail, unless run dry or have contaminated fuel.
The PCM requires camshaft position data to sync the injectors and crank position once running. If recent belt replacement or engine repairs have been carried out, add this to your list. To check the injector sync against cam and crank position is a bit technical. To perform you will require a scope and current clamp.
Quite often the serial data identifies the incorrect timing sensor for position error. This is due to the PCM looking at the camshaft first. Slow rotation speed may be due to a faulty or incorrect battery, so check charge and health status with a suitable conductance tester. Yuasa have a fantastic free online training academy.
Next check relative compression. This is a simple cylinder balance check but when compared with current and rotation calculation will accurately predict correct compression.
Identify
A blocked exhaust or failed open EGR will prevent the correct combustion properties. Exhaust back pressure can easily be proven from the map and DPF pressure sensors. Plotting them with a scope will quickly identify intake or exhaust restrictions. The maximum DPF sensor value cranking or at idle should be 0.5-1.25 volts, 100mbar-1.5psi.
Injector type, solenoid or piezo faults will normally be identified within serial data. A single faulty injector circuit will normally shut down all fuel delivery. It is also worth noting that if a minimum rail pressure is not reached, the injectors will not be activated.
So back to priming. Leaks, faulty rail sensors will all contribute to a non-start.
If you are looking for more information, visit www.ads-global.co.uk for courses and dates, and Autoinform events.
- Draper Expert smoke diagnostic machines
Draper Tools has introduced a pair of smoke diagnostic machines into its Expert range. The Draper Expert Turbo/EVAP Smoke Diagnostic Machine can switch between turbo and evaporation emission control system testing. Also being launched is the Draper Expert Turbo Smoke Diagnostic Machine which can help with a range of leak detection issues. Both models feature a variable pressure gauge that displays flow and fluid indicators, and can be used for finding petrol and diesel system leaks including turbos, intercoolers, manifolds, brake boosters, EGR valves, brake vacuum hoses, cooling systems, air and water leaks.
www.drapertools.com
- Limited spaces still available for first REPXPERT Academy LIVE event
The first REPEXPERT Academy LIVE training day is set to take place on Saturday 16 November at Lincoln College. Spaces are still available, but techs are urged to book now to avoid disappointment. Doors open at 9.30am, and the day runs until 4pm.
- Government aims for new 2035 petrol/diesel ban deadline
A ban on the sale of new petrol and diesel vehicles could come even sooner than expected, with government now saying it intends to bring the deadline forward to 2035 – or even earlier if possible.
- Process, process and more process
People ask me what made the difference this year when I went from being a Top Technician finalist to a Top Technician winner, and my answer is my process. I have worked hard since last year’s final, refining my process, and learning from my mistakes and it thankfully paid off this year. This article highlights the importance of a great process not only in Top Technician, but also in everyday working life, and how a fault, which at first may seem overwhelming, can be simplified and confidently fixed.
The week after winning Top Technician, a 2016 Ford Ranger was booked in for me to have a look at from another garage. The garage’s complaint was that multiple warning lights were present on the dashboard along with multiple warning messages, the power steering was heavy and the indicators and windscreen washers didn’t work from their respective stalks.
As with every job, the first step of my process is to interview the customer and gather as much information as possible. When I questioned the garage owner, he said they had just completed fitting a galvanised chassis. He explained that the vehicle had been fully stripped and rebuilt in the process, and since the rebuild, warning lights, messages and other complaints were now present. The next step was to confirm the fault. Upon starting the vehicle to bring it into my bay, the complaint was verified. The engine management, traction control, anti-lock brake and airbag warning lights were illuminated along with multiple different messages, one of which was a steering assist malfunction warning (see fig. 1).
Complete picture
I then carried out a global scan of the vehicle to get a complete picture of what faults were present and also to see what modules were or were not talking to the scan tool (see fig. 2).
Straight away we could see that multiple modules could not communicate with the power steering control module (PSCM) and restraints control module (RCM). It was also noted that there was a communication issue between the body control module (BCM) and the steering column control module (SCCM).
As the instrument panel cluster (IPC) communicated and reported stored fault codes, I knew it was more than likely a historic fault code which wasn’t related to the issues present. Attempting to communicate directly to the PSCM, SCCM and RCM with the scan tool all returned a ‘no communication’ message, so we knew we were dealing with hard faults that were currently present. Following my process, I decided the next step was to do some research on this particular vehicle using Ford ETIS which is Fords online information portal. This allows me to access wiring diagrams, connector locations and anything and everything related to the vehicle in question. As many a clever man has said, “if you don’t know how it works how can you fix it?”
Thinking of possible causes, I decided to study the wiring for the PSCM and RCM, how the indicators and windscreen washers work and a network topology to allow me to see how all the modules communicate to each other and the diagnostic scan tool.
It was found that the steering column module controlled the indicators and washers and sent the message to the BCM to activate them. As the SCCM wasn’t communicating it now made perfect sense why those functions were not operating. Next, I found that all three modules worked on the high speed can data bus and all were powered by fuses. All the related information and diagrams were printed out and taken to the vehicle so that a test plan could be drawn up and executed.
Plans within plans
Before writing up my plan, I made a visual inspection of wiring under the bonnet and underneath the vehicle. Having had a major overhaul, something as simple as there being a connector left unplugged could cause some of if not all the faults present with this vehicle. Everything looked ok, so I laid out my wiring diagrams and proceeded to write a plan. My plan was to test the fuse for each of the modules to see if it gave me direction, then if all was ok I would look at the communication wiring and how the modules at fault linked into each other and the rest of the vehicle.
All three fuses tested fine so it was onto seeing if there was a common link. Looking through the topology, I found a page which had the PSCM and RCM joined by two connectors. This is where technical information is a must, as dealing with a fault like this it can be very easy to dive in full speed. I don’t want to go straight to a module, for example the RCM, and remove half the interior of the vehicle to find all is ok there and have to spend time reassembling everything! I speak from experience here, and I am sure some of you reading can relate to this.
Diagnostic direction
ETIS showed one connector inside the nearside front wheel arch and the other in the location of the bulkhead of the vehicle. This meant I could test the network without removing anything, saving time and gaining diagnostic direction. I inspected visually to see which of the two connectors was the easiest to access and it was the connector in the nearside wheel arch. Visually the connector looked correct and looked to be correctly latched. However, I decided to double check and upon squeezing the two sides together and audible click was heard meaning the connector was open (see fig. 3).
I then decided to scan the vehicle again to see if this had made any change and every module now communicated and it was also noted the dashboard warning lights had disappeared. I cleared all the faults codes in the vehicle. None returned, and the dashboard now had no messages or warning lights illuminated. The final checks proved the steering assistance now worked correctly and the indicators and washers operated completing the fix.
In the end then a fairly simple fix once it was established how the system worked and where everything was located but without the correct information and a well polished process this job could have taken a very different, and perhaps longer, turn.
- 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.
