Think Before You Lease Your Next Diesel Car

posted on Jun 11 2015 by Kyle McWilton

Think Before You Lease Your Next Diesel Car

Do you constantly do small trips in your car or you do a lot of mileage but only around a town or city... Well! In that case you really need to think before you lease your next diesel car. Heres why;

Since 2009 all new diesel vehicles are required to be fitted with a diesel particulate filter (DPF) this is down to the ‘Euro 5’ emission standards. This was done to cut emissions of diesel particulate (soot) by 80%.

The diesel particulate filter catches soot within the exhaust, its the way in which the filter is cleaned thats the things to be aware of, this process is called ‘regeneration’ this is done in one of two ways;

Passive Regeneration

This is when the regeneration process starts itself due to the car being driven fast or on a long journey down the motor way for instance, the exhaust gets to a certain temperature and begins to burn the soot without the engine control unit (ECU) having to tell the car to do so.

Active Regeneration

This is when the ECU within the car injects fuel into the exhaust to get hot in order to burn off some of the soot. The problem here is if the journey is to short i.e. going to the shop for 5 minutes then the regeneration process will be stopped when you stop the car causing the filter to become blocked.

diesel particulate filter Peogeot

Source: Wikipedia

The basics of the above is if you are not doing long or fast journeys regularly, then your car will be forced to Actively Regenerate the DPF. If your journey is not long enough to complete this process then your DPF is going to end up getting blocked and this can cause all kinds of problems. 

If the regeneration process is uncompleted due to these short journeys then the extra fuel that has been injected into the exhaust will eventually drain into the sump because it is not being burnt. This will eventually cause your engine to run with too much oil and could end in the destruction of your engine. Although this is an extreme situation you are most likely to at least end up with a fault diesel particulate filter that will need to be completely replaced.


We had a customer recently who I worked closely with and supplied many cars. On this particular occasion the customer had decided that he wanted to go for a diesel Mercedes-Benz C Class because it had slightly more torque than its petrol model.

All seemed fine for the first 4 months and then I had a phone call to say that the car had a warning light for diesel particulate filter, he was confused as he had been driving it to work every day with no issues until now. He was doing a 1 mile round trip to work every day in his diesel car and hadn’t realised that the regeneration process would have never kicked in during these short journeys. I got the customer in contact with the dealer who said that the filter wasn’t covered under the warranty and that it was down to the customer to fork out for the bill. This endded up being a £1150 bill! Ouch! This price is obviously going to be different for all cars and models but just gives you an idea of what this mistake can cost and did cost one of my customers.

In short before you lease your next car please think whether or not you need petrol or diesel, as using diesel cars in the wrong way can prove to be a costly decision, a £1150 costly decision. If you already driving a diesel car nad didnt know about this, make sure you give your car a blow out every now and then, we recommend at least once a week just take a different way to work so you can get the filter working properly. This will save you money and keep your car runnning smoothly.