No code; No problem?
Recurring DPF problems but no fault code? Sounds like a job for Darren, that’s for sure
Published: 30 January, 2020
By Darren Darling
The challenge: A 2009 VW Golf 2.0 TDI with recurring DPF problems and no fault codes stored.
This low mileage Golf was presented to us after an unsuccessful trip to the main dealer where the customer was told there was nothing wrong with the car. The customer’s complaint was that the DPF warning light would illuminate every 100 miles; MPG was poor and the car was smoking excessively during regeneration (white smoke). As always, we carried out a thorough assessment of the vehicle to find out why the car was having these issues.
I suspected that the lack of any fault codes was the reason the owner was told that the car was fault-free but clearly we had an issue as the car should not be in regeneration so frequently. We quickly determined this was not caused by a blocked DPF as the DPF was very clean and there were no mechanical issues with the car.
Extended road test
Our next step was to carry out an extended road test while recording live serial data. If the customer had predicted correctly then we would see the DPF symbol illuminate in the next 20 miles or so. Sure enough, the light came on during the road test and the vehicle initiated DPF regeneration. This now gave us an opportunity to monitor the car during regeneration to see what was going on. We noticed that our temperatures during regeneration were too low and that the car did indeed smoke very badly.
Because of the low temperature, the duration of the regeneration was also excessive, taking over 40 minutes to complete. This is not uncommon and we have seen this caused by a software issue on many occasions. We then consulted our database and could see this exact problem with the software version so our next step was to carry out a software update and repeat the extended road test.
The car was noticeably smoother and quieter following the update but it did not initiate regeneration. Although a good sign, we had not seen any evidence yet that it had improved. So, we headed back to the workshop to carry out a forced regeneration so that we could monitor temperature, smoke and regen duration.
We were now happy with the temperatures; the excessive smoke had gone and the regen duration was back to normal. We were confident that the software update had fixed the car.
This job highlights the need for the independent workshop to invest in the correct tooling to carry out software updates because they are becoming more common. No unnecessary DPF cleaning was required to sort this DPF problem out and no parts were fitted to the car.
Another job done and another happy customer.
- 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!
- 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.
- 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.
- 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
