Q Why does my Peugeot keep going into limp mode?

I have a Peugeot Boxer-based motorhome, 2-litre Euro 6 with AdBlue, 2017 registered, with 16,000 miles on it from new.

At approximately 13,000 miles, it started dropping into limp mode and was poor at climbing slight gradients. If I pulled over, switched off for a minute or two then started, it would be OK again for 50-100 miles, but as time went on it progressed to be worse and more frequent.

So, a local garage fitted a new turbo 13 months ago costing over £1,000. This was perfect for about eight months then again it started dropping into limp mode.

I returned it to the garage, which then said it needed a replacement EGR as it was stuck open. The garage couldn’t do the work for some weeks as it was too busy.

However, it was OK again until December, when it started dropping into limp again. Plus, a warning on the dash displayed ‘DPF clean’ while the vehicle was in motion, so I drove it fairly hard to clear possible choked DPF. Now, it seems OK again, but fuel consumption has decreased from 28mpg to 23mpg and I’m not convinced it won’t become faulty again.

How do you recommend I move forward in getting it positively diagnosed or can you suggest what the fault is?

I am reluctant to return to the same garage as I have lost confidence, and it is always too busy.

Alan Maynard A I would have taken the vehicle to a Peugeot dealer or

Peugeot specialist from the outset. Modern vehicles are very complicated and there is no substitute for experience with similar vehicles.

The availability of the manufacturer’s specific diagnostic equipment is also essential. Interpreting the information that you can obtain from the vehicle is not straightforward at all. Codes are clues, hardly ever definitive answers.

I typically think of the combustion process as a river and, if something is not looking right at one end, and there are undesirable effects, you have to look further upstream to find out where things went wrong.

For example, if the particulate filter is getting clogged more than expected, you need to look to the injectors for signs of misfuelling or at the pipes and cooling systems for leaks that can cause excess soot to end up in the exhaust.

With this in mind, I think you should get the vehicle to a Peugeot commercial vehicle site and detail the story so far. You will pay more for labour than you would at an independent but it will know the engine, and will have access to the factory for advice should it be required. I would expect them to want to test the injectors.

The recently lower fuel economy numbers may be due to the change to winter diesel.

This happens in the UK from 16 November until 15 March. The antiwaxing substances are less easily burned.

In my Jeep, I noticed a difference of nearly 3mpg in just a week and it took me

a while to figure this out! Maybe it would be wise to not be overly concerned about the fuel economy in the short-term. It might be a red herring.

On the other hand, it might be as a result of overfuelling by one or more faulty injectors. It could also be that there is no problem with the DPF or the injectors, but simply a faulty sensor for the DPF, which is causing more frequent regenerations to be called for, and this, too, would increase fuel consumption. Sensors can be affected by moisture in exhaust systems of vehicles that are used for short journeys and not fully warmed up and dried out.

The sensor, known as a differential pressure sensor, has pipes attached to it from the front and rear of the DPF. They measure the air pressure at each end and, from the differential between these, work out how blocked the DPF is, using a percentage difference. This is how the

ECU decides when to initiate a regeneration.

If the DPF is excessively blocked, a regeneration may not be possible in the normal way and a workshop can carry out a ‘forced regeneration’ or have to undertake a cleaning process.

So many good reasons to let the experts diagnose it.

Nick Fisher