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• 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.
  
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  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!
  
  
  
  
  
  
  
  

• 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.
  
  
  
  
  
  

• 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.

• Life after lockdown 

  While the lockdown is the reality for now, once restrictions ease, it will be time for mechanics and motorists to accelerate say Kalimex

• JLM Academy launches with DPF Doctor founder Darren Darling at the helm 

  The JLM Academy officially opened its doors on Saturday (20 July). The brainchild of Darren Darling, founder of The DPF Doctor Network, the new Academy is fielding a top-drawer roster of industry trainers, including Darren and Andy Savva, a.k.a The Garage Inspector.

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