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• Shining a light on the root cause failure 

  I was recently asked by a trade customer of mine if we could “simply” program a new headlight module for a VW Golf MK7. They had replaced a control unit due to the dipped beam headlamp not operating. They advised me that after the unit was installed the light started working. with the other lights all operating correctly. However, there was a bulb warning in the dash display Please refer to Fig. 1.
      
  At this point the request would seem normal and a straightforward job so we continued with the task in hand. Correctly programming new headlamp control modules on VAG vehicles will require the dealer tool for this manufacturer, known as ODIS (Offboard Diagnostic Information System). I connected this tool to the vehicle and carried out a full system scan. This is a common practice when attempting to program any control modules as programming errors can occur after the process is done and having a report before and after the programming is very beneficial. It can also aid in any warranty claims.  As you can see the only fault codes being set are “Headlamps No Basic Setting” and another fault code relating to “Right Headlamp Power Output Stage.” Please refer to Fig. 2. These codes were both permanent and would not clear. I expected to see the basic settings code, as the control module had not yet been programmed. However, the other code seemed odd to me initially.
  
  Why programming is rarely straightforward
  I pressed on and attempted to carry out the basic settings of the right-hand headlamp dipped beam control module, which our customer had replaced, but I kept receiving a communication error, as seen in Fig. 3. This seemed very odd as there were no communication fault codes present and all the front lights were operational.
  
  After a few failed attempts I believed there could possibly be another issue with this headlamp which was not analysed initially by the original garage. Using the dealer tool, I accessed the information section and reviewed the wiring diagram for the headlight.
      
  As you can see from Fig.4, there is a main voltage supply, ground, and CAN communication wiring to the headlight. A quick check of each revealed what one should expect when operating properly. Using an oscilloscope, I then checked the CAN bus wiring at this headlight.
  
  To my surprise the CAN bus data signal was corrupted. This seemed very odd. Although the headlight was operational and no-fault codes were present at all regarding CAN communication, it was clear that there was an obvious issue with the data network. There could not have been any communication taking place between the control units on this network. These include the headlight regulation control module and the right/left headlight control modules. After disconnecting each control module in turn, I found the CAN Bus signal had recovered only when disconnecting the right-hand headlamp assembly.
  
  The oversight
  It was now obvious that there was more than meets the eye with this job. After contacting the customer and advising them of my findings they agreed for us to carry out further diagnostic work and identify the cause of the shorted CAN bus signal. The CAN bus wiring connects directly into the headlamp, from the connecter, and then into a control unit. According to the diagram, the connector is part of the headlamp assembly. I removed the right-hand headlamp assembly and located the control module which the CAN bus wiring goes to. I removed the headlight control unit from the bottom of the headlight assembly and found water intrusion present, causing the CAN bus signal to be shorted. See Fig.7. Unfortunately for the customer, this vehicle required a new headlight assembly and control module.
      
  A replacement headlight control module and headlamp assembly were both installed. The basic settings function was run once again, using the dealer equipment. This time the function was successful. The headlights needed to be put into a setting position and then physically adjusted on a beam setter before confirming the adjustments were complete. The module then saved this adjustment as its basic setting. What initially seemed a straightforward job turned into a bit of a nightmare due to incomplete diagnosis. Many aftermarket garages will often not allow the diagnosis to take place elsewhere. I carry out a lot of programming for various independent garages across the South West and find this can be a regular occurrence. Correct reporting is essential. Before-and-after reports are a necessity and will often protect you against any shortfalls in the initial diagnosis. These reports include full system scans before and after the programming has taken place, and any other reports generated by the diagnostic tool in use for both failures and successes.
  
  
  

• Don’t follow the fault code – follow the smoke signals  

  When this 2010 Vauxhall Insignia arrived at our workshop recently, we were asked the common question: “How much to clean my DPF?” As always, we informed the customer the first thing we needed to do was to undertake an assessment, so we could determine why the car was having DPF problems and what was required to fix it. This assessment is much more than a fault code read, often perceived as a ‘diagnostic check’ and this highlights the difference. The fault codes present on the car were ‘P2453 DPF Pressure Sensor A Circuit Range Performance’ and ‘P2458 Mass Air Flow Sensor Performance’.
      
  Opening the bonnet, we were not surprised to see a new MAF sensor and a new DPF pressure sensor. This is frustrating as the owner has paid for these unnecessary parts to be fitted on the basis that ‘the computer said they were faulty’.
      
  Looking at the DPF pressure sensor fault first, the ECU was reporting a circuit range fault. This may look like a faulty sensor but is in fact caused by excessive DPF pressure. The pressure is measured by the sensor. The signal is sent back to the ECU as a voltage so the excess pressure causes an excess voltage signal and in turn the ECU reports what it can see. The DPF back pressure was in excess of 150MB at idle indicating we must clean the DPF after addressing the cause of the problem.
      
  Moving on to the MAF performance fault. Again, the ECU only reports what it sees as incorrect; in this case incorrect air flow. This is obvious when analysing live serial data so our next step was testing the intake system for leaks to confirm our suspicions. As you can see there was a significant leak from an intercooler pipe. We found a cause for both issues. The split pipe would have initially caused the MAF fault but in turn would lead to the DPF pressure sensor fault due to the excessive soot being produced with the major boost leak.
      
  After consulting the customer, we repaired the car, replacing the intercooler pipe. Root cause now taken care of we had the easy part – cleaning the DPF. Our weapon of choice for DPF cleaning is always the JLM Lubricants’ Clean & Flush. With the step one chemical we left it to soak for a few minutes. After running the engine for a few minutes, we flushed the DPF out with the step two JLM DPF flush.
  
  After the clean we had a healthy 6MB of back pressure in the DPF and the pressure sensor fault was cleared. An extended road test confirmed the fix.
  
  
  
  
  
  

• Third Time Lucky 

  Today’s vehicle case study is a 2011 Vauxhall Insignia which came to us because of a loss of power. It had been looked at twice by another garage to no avail. As with every diagnostic job, we started by questioning the customer so we can gain as much background information as possible. After this initial phone call, I was confident of the type of fault being presented. This was confirmed at the subsequent diagnostic assessment. On running the global fault scan, we found multiple faults relating to the turbo system with ‘underboost’ and ‘overboost’ codes alongside DPF soot accumulation codes logged in the memory of the ECU.    
      
  We followed our industry-leading DPF assessment, learned through the DPF Doctor Network practical training programme. Firstly, using smoke testing we found the split intercooler hose (see Fig.1) which coincided with our P0299 turbo underboost code. However, the assessment does not finish when we find a fault. We see it through to the end. Further testing revealed that the vacuum control solenoid was not controlling the vacuum to move the turbo actuator which then mates up with the turbo overboost code stored. Using the serial data, we could see there was also EGR and air flow issues caused by running the engine with a boost leak.
      
  Excessive soot and black smoke from the engine had choked the intake system and EGR valve. To tackle this mass of build-up soot and carbon we used the JLM Intake Extreme Cleaning Toolkit to break down the carbon. We removed the intake pipe and could see the thick ‘black death’ in the intake manifold (see Fig.2). As the chemical worked its way through, we could see on the serial data that air flow and DPF pressures were coming down. An endoscope was sent down the intake where we could see first-hand how well the intake clean had worked. We were impressed! This removed the turbo lag and flat spot at lower RPM.  
  
  Rectification
  We went on to rectify the remaining faults. We added a bottle of JLM Extreme Clean to a full tank of fuel and took the car on the road to monitor some more live data and watch the Extreme Clean work its magic on the DPF system during regeneration. By the end of the road test the DPF pressures were down to single figures which is just what we would expect from a three-stage clean. To finish the job, we added a bottle of JLM Engine Oil Flush to the engine and carried out an oil and filter change to ensure any chemical from the intake clean was not in the engine’s vital organs (See Fig.3).
      
  Our customer was absolutely delighted given he was expecting the worst after the previous garage had tried twice to fix. We use the Engine Oil Flush and an Emissions treatment on every vehicle we service. Customers always comment on the increased MPG and how clean the oil is after the flush has been used.
      
  We have used JLM Lubricants’ products since we opened our garage doors in July 2020. I am pleased to report that we have never been let down by the quality and with the support received from Kalimex, UK distributors of JLM, Darren Darling, Founder of the DPF Doctor Network, or even JLM Managing Director Gilbert Groot. The support in our network is absolutely second to none.
  
  JLM products used
  Diesel Intake Extreme Cleaning Toolkit J02280 and J02285: This is a highly effective yet simple way to clean the entire combustion and exhaust system on a neglected diesel engine. With this low-cost kit you can quickly restore performance and reduce emissions. Developed in collaboration with diesel professionals including Darren Darling, the system delivers a controlled dose of powerful clean and flush fluids that gently decontaminate the air intake, combustion chamber, valves, injectors, and variable turbo vanes of a dirty diesel engine. No removal required. It is much more powerful than an additive added to the fuel tank or an aerosol air intake spray. Used with the two dedicated and chemically advanced cleaning fluids, each one addressing different contaminations to restore the original air flow to the engine.
      
  Extreme Clean J02360: A very strong all-in-one blend of high-end chemicals to detox the entire fuel system including turbo, EGR and DPF.
      
  Engine Oil Flush J04835: This gets the most out of new oil by cleaning out more dirt and contamination when changing the old oil and when used regularly, will not allow the build-up of dirt to develop again. It reduces fuel consumption and improves engine performance.
      
  Emission Reduction Treatment J02370: A shot of this additive in the fuel tank will reduce the emissions and help to prevent a MOT emission fail or resolve a post-MOT emission fail. It also helps keep the exhaust and CAT clean.
      
  For more information visit www.jlmlubricants.com and www.the-dpf-doctor.com
  
  
  

• Mercedes-Benz: Code conundrum 

  This low mileage (38,000 miles) Mercedes A200CDI was presented to us recently with suspected DPF problems. The car had been well maintained with a full service history but was lacking in power. We were asked to assess the vehicle. So, what was going on?
      
  We started with a global scan of the car to see what fault codes were present. This would give us some direction. As always it is important we do not simply read a fault code and rely on the diagnostic tool to do the job. We were presented with three fault codes: P0299- Boost pressure of turbocharger is too low; P2263 – The boost pressure deviates from specified value; P2002 – DPF efficiency below threshold.
  
  Direction
  We now had a clear direction. The next step was to carry out some tests to determine what was causing the problem. In so many cases we see parts that are changed on the basis of fault codes. What this means is that a new turbo or DPF is fitted when in reality they are not the solution. The problem remains, at great cost to the customer.
      
  With any low boost condition fault, we always start with a smoke test to rule out any leaks. Tests on this vehicle showed we did have a boost leak. We then looked at the DPF pressure so see if it was too high or too low. This gave us some direction. On live serial data the DPF pressure was reading zero so we could be dealing with a dead sensor or a wiring issue, or perhaps neither. We then moved on to measuring the actual DPF pressure and testing the plausibility of the pressure sensor. This was where, pardon the pun, we were really motoring. The backpressure from pre-DPF was measured at 68mb at idle. Was this the cause of the low boost problem? Was the DPF actually blocked? So why did the pressure read 0 on live data? Was the sensor dead?
      
  We continued with our assessment to determine the answers to these questions. We then tested the backpressure post DPF. This also measured 68mb at idle so our pressure was actually coming from downstream of the DPF and not the DPF itself. This also explained why we had 0mb on live data as the DPF pressure sensor is a differential pressure sensor, not a back pressure sensor. The difference in pressure pre and post DPF was actually 0.
      
  This model of vehicle uses an exhaust flap at the rear of the exhaust to divert exhaust gases via the low pressure EGR valve so this was the next place for us to take a look. Sure enough, the exhaust flap was seized in a closed position causing an exhaust restriction that in turn caused a low boost condition. The flap/motor was replaced and we now had a differential pressure reading of 4mb at idle with boost pressure now meeting the desired levels. No unnecessary parts were fitted. Job done!
  
  
  
  
  
  
  
  

• DPF maintenance 

  Achieving the tough vehicle emissions levels under Euro 5 legislation requires a Diesel Particulate Filter (DPF) to be fitted to collect carbon soot particles generated from the combustion process in a diesel engine.

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