The modern fleet vehicle has never been more complicated. Downward pressure on fuel consumption and CO2 means the latest models are achieving ever-higher efficiency from ever-lower cubic capacity, while consumers expect high durability with increasingly wide service intervals and long warranties.

Evidence suggests cars are making fewer visits to a workshop than ever before. New figures from Trend Tracker showed a 20% drop in routine servicing and repair jobs during the last decade – great news for fleets looking to minimise downtime.

But this reduced exposure can be a double-edged sword. Less frequent visits can mean problems go unnoticed, and while leasing companies are reporting constant improvements in reliability across the board, new technology has created a few new headaches for fleets.

The engine warning light appears to be one such perennial problem. This can be triggered when any one of what could be more than 100 sensors under the bonnet gives an anomalous reading to the engine management system, and can be accompanied by the car switching to a performance-reducing ‘limp home mode’.

But while not all problems are serious, Mark Connor, operations director at Zenith, says it can be unnerving for drivers: ‘There are many reasons why a warning light might trigger, but from a driver’s perspective – who typically has less technical experience – the impact is the same,’ he explained.

‘The driver might experience the vehicle going into ‘limp home’ mode, and it might lead him to think that a dealer has mis-diagnosed a problem if he experiences this similar output on more than one occasion.’

Problems aren’t always electrical. Increasingly stringent emissions standards, not only in Europe but globally, mean manufacturers are adding new filters and recirculation systems to control harmful exhaust output. Of these, it’s the diesel particulate filter (DPF) which is the most regular cause of concern for drivers.

DPFs have been mandatory since Euro 5 emissions regulations were introduced at the start of 2011. It’s a filter in the exhaust designed to trap soot, usually burning this off (known as regenerating) while the engine is hot.

But – as with the early catalytic converters – their proliferation means they’re not always fitted to cars which suit the technology. Shorter journeys mean the DPF doesn’t always reach the temperature needed to regenerate, and can be prone to clogging, eventually causing running problems. Malcolm Roberts, fleet services manager at Hitachi Capital, says this results in an average three-day downtime to repair.

The regeneration process is also widely misunderstood. If the car detects reduced airflow through the DPF it can actively raise the exhaust temperature by injecting extra fuel, but the associated rise in fuel consumption and smell of diesel has been known to be mistaken for engine faults if the driver is unaware of the technology.

Phil Turle, operations manager at ALD Automotive, explains: ‘DPFs cause a lot of downtime. If it’s a business car you can usually speak to fleet people who are switched on, but with smaller fleets you’re usually dealing with end users, and nobody likes to be told they are doing something wrong.

‘We’re looking at putting it into contracts this year. It will advise that the vehicle may have a DPF and that it could create problems if the driver is not aware of the regeneration cycle process. It’s all about making the customer aware of potential issues and the technology in today’s vehicles.’

Ironically, it’s the systems most drivers won’t notice which are the ones having the most impact. Leasing companies reported no issues with stop/start systems, while the latest downsized petrol and diesel engines and hybrids are proving as reliable, if not more so, than their predecessors. Electric and hybrid vehicles are also tending to come in under their predicted SMR costs.

Connor says: ‘Hybrid and electric vehicles have such a gentle power delivery, and we are seeing that they use less tyres. Also, with the electric generators helping slow the vehicle down we are finding they need less brake replacements.’

But it’s never been more important for drivers to understand the latest additions to their vehicles, to avoid what can be needless downtime. This also applies to independent repairers, who as a result of Block Exemption are able to service and repair vehicles without affecting warranties. Turle adds that they’re not always aware of minor software updates, which can avoid the need for expensive mechanical repairs.

Turle says: ‘It makes more sense to us to have a vehicle serviced within the Franchise network, with many manufacturers offering fixed priced servicing and the backing of the manufacturer regarding goodwill, we shouldn’t always assume independent route is the cheaper option all the time.’

However, feedback from the leasing industry suggests cars have never been more reliable, and manufacturers have never been keener to work with customers to iron out the problems which do persist. Provided drivers understand the systems they’re presented with, the latest additions to company vehicles should present relatively few headaches.

On the horizon – Euro 6

The latest Euro 6 emissions standards come into force next September, setting tough new limits on toxic NOx and Hydrocarbon content in diesel engine exhaust output.

While some manufacturers – such as Mazda with its SKYACTIV-D diesel engine – have managed to come under the threshold using an optimised combustion process, this next stage in emissions control will usually require extra filters or a urea solution similar to AdBlue used in heavy goods vehicles. This will require regular refilling to avoid warning lights or the car stopping altogether.

‘It’s touching the surface now,’ says Phil Turle of ALD Automotive. ‘People don’t like the process of refilling. We’ve had a couple of drivers who have had problems with contamination, because they think it’s washer additive. Drivers are not happy as they’re charged €25-35 for an AdBlue top up – they do query it.’

Top 5 vehicle faults

1. Batteries

Still a leading cause of breakdown calls, but difficult to diagnose whether the vehicle or driver is at fault. This usually results in the vehicle being jump-started at the roadside and taken to the nearest garage, but rarely results in a new battery being fitted due to wear and tear.

2. Engine Warning Lights

Caused by an unexpected reading from any of the engine’s sensors, engine warning lights are a frequent cause of concern for drivers. The problem is often a faulty sensor and can be repaired quickly, but as it can suggest other faults it should be reported to a garage as soon as possible.

3. DPFs

Increasing in frequency as diesel particulate filters are found on a larger share of the vehicle parc, DPFs can block if they aren’t able to come up to temperature. The result is an unnerving warning light, reduced performance and economy and a diesel smell as the car injects additional fuel to clear the blockage.

4. EGR Valve Cooler

Another emission control system, exhaust gas recirculation systems divert some of the exhaust gases back into the engine to combust harmful gas output. But these are temperature controlled with coolant, and faults can cause this to leak into the exhaust system resulting in smoking and starting issues.

5. Fuel Filters

Used to remove contaminants such as rust, sand and water before they reach delicate fuel injectors, diesel filters can clog if summer formula fuel is used during the winter, causing waxy deposits to form. The result is reduced performance and usually a replacement is required.