Currently reading: Autocar test shows worse economy after Volkswagen diesel fix
Exclusive test finds a Touran to be less fuel-efficient after receiving Volkswagen’s emissions fix

An Autocar test has revealed that the fix Volkswagen is applying to diesel-powered cars fitted with its emission-cheating software can have an adverse impact on fuel economy in the real world.

VW fitted more than 1.2 million cars sold in the UK with software that allowed the car to know when it was undergoing emissions tests in order for its NOx emissions to reach legal levels. It is now having to apply a technical fix to all affected cars and has done so to more than 600,000 at present.

The Autocar test was conducted at Millbrook Proving Ground to the standard set by the True MPG real-world test cycle of our sister title What Car?. The test used the latest international standard equipment for testing vehicles in a scientific and repeatable manner to industry standards.

Comment: what does our VW dieselgate fix test prove?

It revealed that while NOx emissions were almost halved from 0.639g/km pre-fix to 0.351g/km post-fix, our test car’s combined fuel economy had fallen from 50.72mpg to 47.61mpg. This means that its CO2 emissions increased from 147.3g/km to 156.9g/km, a change of 6.5%.

The car we tested belonged to reader Jonathan Mudd and was a 2013 Volkswagen Touran fitted with the EA189 1.6-litre diesel engine, one of three units sold in the UK by VW fitted with the cheat software that needs correcting.

Vw news 165

The economy drop is at odds with VW’s insistence that its technical fix has no impact on a car’s performance or economy. VW’s claim is based on back-to-back NEDC tests — the lab-based test cycle by which VW is being measured by the authorities — and has been verified by the KBA, Germany’s motor vehicle regulatory body.

Diesel engines: your questions answered

Upon completion of his car’s technical fix, which took five hours, Mudd was presented with a ‘Certificate of Completion’ that stated: “The successful implementation of the measures does not adversely impact the engine performance, fuel consumption, CO2 emissions, torque or noise of your vehicle.”

Back to top

On that point, Mudd said: “Looking at the pre and post-fix test data for fuel economy, it’s concerning that the data doesn’t back that claim up. My car is now less fuel-efficient than it was before the required technical measure was carried out and means I’ll be out of pocket as a result.”

Our Millbrook test assures repeatability of the economy and CO2 figures to within 1% on any subsequent tests and is typically accurate to within 0.5%, so the margin of error is not enough to account for the 3.11mpg drop in economy.

Results for NOx emissions are less reliable from one test, however, and are best recorded as an average of three tests. That is why Autocar is only focusing on the impact the fix has had on fuel economy.

VW disputes our findings. It says there are more than 20 variables that can impact a test result such as ours. It would not, however, provide further details of those variables when asked to do so by Autocar.

In total, three engines are being fixed in the UK by VW: 1.2, 1.6 and 2.0 versions of the EA189 engine. The number of different combinations of car, transmission, engine and so on comes to 750, meaning VW needed to come up with 750 different fixes.

Vw news 169

It is understood that the fix to the 2.0-litre diesel models is the most complex.

Back to top

Our test focused on the impact on real-world economy of the fix that VW has applied to the engines, but the 2.0-litre engine type is also subject to a growing number of case studies and reports that the fix is causing breakdowns in cars that have had it done.

Diesel engines: what comes out of your car's tailpipe?

A report by the Volkswagen Diesel Customer Forum (VDCF) last month said owners of postfix VWs with the 2.0-litre diesel had experienced breakdowns, increased fuel consumption, reduced performance, increased exhaust smoke, excessive regeneration of diesel particulate filters (DPFs) and DPF failure.

Exhaust gas regeneration (EGR) valves, turbochargers and fuel injectors are also said to have failed and others report their cars having entered limphome mode or their engines having become noisier.

VW claims many of these faults could be down to poor maintenance, with some of the cars even missing their DPFs. None of the issues is related to the fix, VW asserts. 

VW hopes to have the fixes completed to all 1.2m by the autumn. The German manufacturer says less than 1% of owners have so far reported problems after the fix, which translates to around 6000 customers.

Insight: Is it time to give up on the diesel engine?

In a statement, Volkswagen said: “Far fewer than 1% of UK customers who own affected Volkswagen Group vehicles that have received the technical measures have reported any issues.

“That means that more than 99% of customers are satisfied with the application of technical measures, which of course are carried out free of charge. We make it a priority to look at the vehicles of the very small proportion of customers who report any issues.”

The VDCF claims the number of complaints and cars affected by the fix is actually much greater and that VW has not kept a log of complaints. The VDCF has urged the government to consider prosecuting VW.

A class action case being built against Volkswagen is gathering data in a survey of owners in the UK claiming their cars have been affected by the diesel engine fix.

Back to top

In an email sent to those seeking class action by one of the law firms, Harcus Sinclair UK, it was claimed that of the 7504 survey respondents who had had the fix carried out on their car, 3925 have subsequently experienced a problem with their vehicle. Of those, 2103 have experienced reduced fuel efficiency, 526 have had their car enter limphome mode, and 200 claim to have been told by a garage that their fault is related to the fix.

Volkswagen's response to our test

“Volkswagen was not provided with sufficient information concerning the testing criteria nor an explanation of how such a cycle is representative of real-world driving.

“Volkswagen also notes that comparative fuel consumption measurements must be carried out very meticulously with, among other things, due attention to cycle profile, duration, the type of test rig and settings (including aerodynamic resistances, coast down data and load adjustments), the system used for the measurement and the scatter of test numbers.

“To attain a level of consistency, one measurement is not sufficient and more measurements must be completed on an identical vehicle. Further, as Autocar is aware, in any standard comparative analysis, comprehensive vehicle preparation would always be critical to the reliability of the values.

“It should also be noted that the relevant approval authorities have approved the technical measures and that during the development of the technical measures, Volkswagen worked with care to ensure that fuel consumption figures in the homologation cycle and on the road remain the same when compared with the previous software. If increases in fuel consumption were detected during the development phase, the software was revised and retested.”

- Despite VW’s claim, Autocar supplied all test details requested by the manufacturer.

Vw news 166

Back to top

How the What Car? True MPG test is carried out

The test is conducted on a rolling road under strictly controlled lab conditions. This means the test is repeatable, because outside variables such as weather and traffic don’t affect the results.

The test is carried out at Millbrook Proving Ground, a centre used for regulatory approved vehicle emissions testing. Millbrook has the latest equipment for testing vehicles in a highly scientific and repeatable manner.

First, we inspect the car to check its roadworthiness. We then weigh the car, and that weight is used to calculate the rolling road (or dyno) loads that replicate the resistive forces acting on a car when it’s being driven on the road.

Next, the tyre pressures are checked and an exhaust connection is fitted, allowing the car’s emissions to be measured. We also carry out an exhaust pressure check to identify any leaks.

The climate control is turned on and set to 21deg C. Headlights are switched off during testing. Any other electrical equipment — for example, stereo or heated seats — is also switched off.

Next, we carry out a pre-conditioning test on the car. This is, in effect, a dress rehearsal, to check that there are no problems and to make sure that all the cars we test are in the same state before they start the True MPG test.

We leave the car to ‘soak’ at 23deg C so that every car starts the test with the same engine temperature. We don’t place the car’s battery on charge while this is going on.

Then it’s time for the True MPG test. We sample the tailpipe emissions — carbon dioxide (CO2), nitrogen oxides (NOx), carbon monoxide (CO) and unburnt hydrocarbons (HC) — on a second-by-second basis and collect bagged samples of each phase of the test for our calculations.

Our results are summarised by different phases of driving — town, motorway and rural — and fuel economy figures are calculated from CO2 results. Finally, our headline True MPG average is calculated.

Back to top

The post-fix problem: how one reader's Golf has serious issues following its fix 

Hampshire-based reader Richard Frame had his Volkswagen Golf 1.6 TDI’s fix completed in January.

The next day, Frame’s car began to judder in low gears, and the fan went into overdrive when the engine was turned off. He took the advice of the local VW garage and drove it at above 45mph in fourth gear for 15 minutes, in a bid to regenerate the diesel particulate filter (DPF).

Nine days after the fix, the car wouldn’t start, so Frame returned it to the VW garage.

Three days later, he was told the car needed a new exhaust gas regeneration (EGR) valve. VW eventually agreed to cover the cost (about £1300) but wouldn’t say this failure was in any way linked to the emissions fix.

Vw news 170

This procedure took a week, at which point Frame was informed that the garage had found a faulty injector. VW also agreed to pay the total cost for this (about £700).

When Frame collected his repaired car in mid-February, he still noticed a significant difference. In early March, VW recalled Frame’s car because the EGR valve had been fitted with the wrong bolts. He expressed his concern about the Golf still sounding very different and juddering after it had been started. VW checked the other injectors but determined that none of them was faulty.

Back to top

Since then, Frame said he has repeatedly experienced strong burning smells from the engine after short journeys and the fan runs rapidly to cool the engine.

He said: “Since the fix, the engine needs to regenerate so much more — on average, once every two weeks — which means that fuel efficiency has also been affected.”

Frame contacted VW on 20 March about the ongoing issues with his Golf and was told a case manager would call him back. At the time of Autocar going to print, he had still not received that call. He said: “Before the NOx emissions service action was applied, my wife and I had been very happy with the car and with its performance.

“Now, the car sounds like a van and smells like a lorry. Volkswagen has picked up the bill so far but at no point has it accepted there is a link between these additional problems and the emissions fix, when I believe this is the obvious cause.

“We have now lost all faith in how reliable our car is — and each and every time we drive it, we’re genuinely concerned that something else will go wrong. This is our only car and we have a young family.”

Read more about the VW scandal:

Greed, lies and deception - the VW Dieselgate scandal laid bare

Volkswagen dieselgate emissions scandal: 20,000 UK cars being fixed a week

Volkswagen denies its Dieselgate fix causes breakdowns

VW emissions scandal: one year on

Volkswagen to abandon small diesels in favour of mild hybrids

Mark Tisshaw

Title: Editor

Mark is a journalist with more than a decade of top-level experience in the automotive industry. He first joined Autocar in 2009, having previously worked in local newspapers. He has held several roles at Autocar, including news editor, deputy editor, digital editor and his current position of editor, one he has held since 2017.

From this position he oversees all of Autocar’s content across the print magazine, website, social media, video, and podcast channels, as well as our recent launch, Autocar Business. Mark regularly interviews the very top global executives in the automotive industry, telling their stories and holding them to account, meeting them at shows and events around the world.

Mark is a Car of the Year juror, a prestigious annual award that Autocar is one of the main sponsors of. He has made media appearances on the likes of the BBC, and contributed to titles including What Car?Move Electric and Pistonheads, and has written a column for The Sun.

Join the debate

Add a comment…
V8 mechanic 16 March 2019

German cars lol

The fact is that the design of the egr valve hasn’t changed since 1972. For all it’s initial emissions attributes when the valve “clogs” the subsequent black smoke is thousands of times more toxic. In a matter of days that toxicity overtakes any advantage gained in the preceding year. Manufacturers and governments recognise this but are afraid to be implicated. Now with the strength of the internet this collusion is being discovered. 

pablomorgan 31 October 2017


VW Emissions fix causing problems? Golf 1.6 TDI cabriolet driven perfectly since bought Jan 15. Had emissions update Jan 17, now gone into limp mode owing to low fuel pressure. VW dealer diagnosed a misfuel at 10k miles has caused it - is this likely, as now done 42k? Or is it an Engine Management system fault? Faced with a £6k bill which is almost what the car is worth!
405line 13 July 2017

So let's get this straight

Has it not occured to people that VW appears to have cheated because they could not engineer the engines to perform as well as the competition and when they do meet their emissions targets the power is down etc etc etc...this appears to be the reason for not being able to tell the truth regarding the emissions of their engines in the first place.

Philp Huang 15 September 2017