If you are considering leasing a car with a diesel engine, it's worth being aware that most diesel vehicles are fitted with a Diesel Particulate Filter (DPF) and/or require Adblue Solution/exhaust fluid. This is so that the vehicle can meet environmental regulations.

A vehicle fitted with a DPF is not always suited to short journeys or start/stop town driving.  AdBlue Solution/exhaust fluid requires topping up, and it is not covered by the manufacturer's warranty or a maintenance contract.

Your account manager will be able to advise you further. 

Your vehicle and its Diesel Particulate Filter (DPF)

What is a Diesel Particulate Filter (DPF)?

If you drive a modern, diesel car it is likely to be fitted with a Diesel Particulate Filter (DPF).  This is a device that reduces harmful gases including carbon dioxide and nitrogen oxides which are considered to contribute to climate change.

How does a DPF work?

In order to limit the amount of small soot particles contained within the diesel exhaust gases passing into the atmosphere, modern diesel vehicles are usually equipped with a diesel particulate filter (DPF).

This filter forms part of the vehicle's exhaust system and is similar in construction to a catalytic converter.  It traps and stores solid particles or ‘soot', produced by diesel engine combustion, in a honeycomb matrix made of a ceramic material.

When the amount of soot in the filter reaches a specified level, this needs to be reduced to maintain the filter's function.  This reduction of the particulate matter is called regeneration and must be performed periodically.  A DPF can remain effective for a long service life through repeated cycles of trapping particulate matter and regeneration.

How does ‘regeneration' occur and when can it cause an issue?

Usually this regeneration is carried out by the vehicle's electronic control systems raising the exhaust gas temperature, during normal driving, without the driver being aware.

If however the vehicle is only driven either on short journeys, or at low speed, then it may not be possible for the exhaust gas to reach a high enough temperature for regeneration. 

In this situation, the DPF warning light on the dashboard will be illuminated.Depending on the vehicle manufacturer, the DPF warning light will look similar to one of the images shown below. 


As soon as possible after the DPF warning lamp illuminates, you should drive the vehicle at a speed above 40mph until the light goes out.  Depending on the amount of accumulated soot this can take up to 30 minutes.  It is important that this is done at the earliest opportunity.

Always drive the vehicle in a safe manner according to traffic conditions and obey traffic laws when driving. We reccomend using a motorway where possible.

If, after the DPF warning light illuminates, the vehicle continues to be driven in a style whereby the exhaust gas temperature cannot be raised sufficiently, then the vehicle's electronic control system performs the following actions to protect the DPF and the engine:

The engine warning is illuminated together with the DPF warming lamp, which, depending on the vehicle manufacturer, will look similar to one of the images below.


The vehicle may also enter "fail-safe" mode and limit engine speed to a maximum of 3,000rpm.

​How do I fix my vehicle if the Engine Warning Light is illuminated along with the DPF warming lamp?

To recover from the condition described above, SERVICE REGENERATION of the DPF is required. 

This can only be carried out by an approved workshop with the appropriate diagnostic equipment for your make of vehicle.  In addition, whenever Service Regeneration has been carried out, the engine oil and filter must be replaced.

To avoid the need for Service Regeneration it is very important to drive the vehicle at higher speeds as soon as is practical after the DPF warning light illuminates.

Once the engine warning light is illuminated, driving at higher speeds will NOT regenerate the DPF.

If Service Regeneration is required the vehicle manufacturers do not class this as a fault with the vehicle and it will NOT be covered under your vehicle's warranty or maintenance package, you will be liable for the cost.

AdBlue/Exhaust Fluid and your leased vehicle

If your leased vehicle has a diesel engine, chances are it requires AdBlue solution/exhaust fluid.  It's worth taking a few minutes to understand what AdBlue/exhaust fluid is and how it needs to be maintained throughout your leasing contract. 

What is AdBlue?

AdBlue is the registered trademark for a solution that reduces emissions from the exhaust of UK diesel vehicles.  This is so that they comply with Euro 6 emissions standards.  Adblue/exhaust fluid is a highly purified colourless liquid.  It contains demineralised water and urea (32.5%).

Which vehicles require AdBlue/Exhaust Fluid?

If your vehicle is a modern diesel vehicle using SCR (Selective Catalytic Reduction) technology, it will require AdBlue/exhaust fluid. 

It can be difficult to tell which vehicles require AdBlue/exhaust fluid just by looking at the model description.  It is best to check with the manufacturer directly, or contact your Synergy Account Manager.

How does AdBlue/Exhaust Fluid work?

AdBlue/exhaust fluid is injected into the catalyst of the SCR system and reduces harmful emissions (nitrogen oxides).

AdBlue solution/exhaust fluid is used in a dedicated tank in the vehicle, which is separate from the engine.  To function correctly, the AdBlue/exhaust fluid tank of your vehicle must be refilled with AdBlue solution/exhaust fluid when required.

When does AdBlue/Exhaust Fluid need to be topped up?

Depending on the make and model of your vehicle, AdBlue/exhaust fluid will last between a range of 3,500 -13,000 miles.

For many drivers, the AdBlue solution/exhaust fluid top-up can be carried out at the same time as the vehicle's scheduled service for an additional fee.

However, it is possible that the AdBlue solution/exhaust fluid will need topping up in-between servicing in the same way that fuel, oil and washer fluid may need to be topped up.

If a warning light informs you that the AdBlue solution/exhaust fluid needs refilling, it is important that this is carried out at the earliest opportunity.  The warning should not be ignored.  Most vehicles will not restart if you run out of AdBlue/exhaust fluid.

Is AdBlue/Exhaust Fluid covered under my maintenance contract?

AdBlue/exhaust fluid is not covered under the majority of maintenance contracts.  It is the driver's responsibility to ensure that AdBlue/exhaust fluid is kept topped up and to pay any costs for doing this. 

How is AdBlue/Exhaust Fluid topped up?

Each vehicle manufacturer has a different method of topping up AdBlue/exhaust fluid.  AdBlue/exhaust fluid tanks can also be situated in different locations in different vehicles, but most vehicles we supply are set up like the image below. The blue cap is the Adblue tank.

​Important Points

  • It is the driver's responsibility to ensure that AdBlue/exhaust fluid is kept topped-up
  • It is the driver's responsibility to pay for any AdBlue/exhaust fluid top ups – this is not covered under maintenance plans
  • Ensure the AdBlue/exhaust fluid tank is refilled as soon as the warning light comes on
  • If the AdBlue solution/exhaust fluid runs out the vehicle will not restart once it has been switched off 
  • To restart the engine, AdBlue solution/exhaust fluid must be added first 
  • If the wrong fluid is poured into the AdBlue/exhaust fluid tank do not start the engine.  Contact CA Cars or Fleet assist Immediately.
  • If Adblue/ exhaust fluid is poured into the fuel tank, do not start the engine. Contact CA Cars or Fleet assist Immediately.
  • Any Mistake in the fueling, topping up of adblue or DPF regeneration will not be covered by CA Cars, you will be liable for all costs incurred to repair the vehicle.

CA Cars opening hours

SalesMonday–Friday 09:00–18:00
AdministrationMonday–Friday 08:30–17:30
ServiceMonday–Friday 08.30–17.30
Vehicle collection / returnMonday–Friday 10:00–16:00

Out-of-hours breakdown emergency contact number:

0780 366 0051 → Option 1