Diamond Dave

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Our expert Diamond Dave runs his own motorhome workshop, and now he offers advice on how to prepare your motorhome so that it passes its MoT first time!

I’ve been asked how the recent issues regarding Volkswagen and emissions claims affect those with motorhomes. Many modern vehicles’ road tax is based on the vehicle’s CO2 emissions, quoted as grammes per one hundred kilometres; this is not generally applied to light commercial vehicles, although no doubt it will be in future. In this article I'll look at what that might mean for you.

Your motorhome’s MoT is crucial, too. You could find it failing for something that could be easily rectified – save yourself time and money by following my handy hints.

How to pass an MoT

I’d like to include some hints and tips this month about how you should present your vehicle for its annual inspection. I don’t carry out MoTs in my workshop: I use a local MoT station that has a large, 5.5-tonne lift, so can handle most motorhomes.

The vast majority of vehicles that we present for testing are also in for a service, but we get the MoT done first so that if any issues arise we have time to deal with them.

To be fair, we don’t get many MoT failures – the majority of owners look after their ’vans well – but when we do, nine times out of 10 it’s for something silly like a numberplate lamp not working, the headlight aim too high, or even the wrong dip pattern (Continental headlights have a raised illumination to the right instead of the left).

The majority of these ‘detail’ failures could be avoided by a few simple checks. So, before you take your vehicle for its test, here are a few things to look at:

  • Ensure all the road lights work (reversing lights aren’t part of the test, but check them anyway).

  • Make your headlights dip the correct way. At night park facing a wall or garage door and check that both lights are aimed at the same level. As a rule of thumb, from two metres away the horizontal top edge of the light pattern should be no higher than the centre line of the headlight.

  • Check your tyres for their tread depth, inflation and general condition. Sidewall cracks will only fail the test if the cord structure of the tyre is visible, but bear in mind that cracked sidewalls will get worse.

  • Make sure that your windscreen wipers clear the full screen effectively.

  • Check that your washer jets are aimed properly, and that the washer reservoir is full.


The older your motorhome, the more maintenance you are likely to be doing. For instance, Nigel Donnelly points out common problems with the Mark 1 Fiat Ducato here, including potential causes for MoT failure. We also have an older in-depth article showing how to prepare your 'van for its MoT here. And I discuss what to do when you spot various dashboard warning lights here.

Exhaust: the options

Over the years, the world’s best scientists have come to the conclusion that CO2 (carbon dioxide) is bad for the environment and, because CO2 is a by-product of the internal-combustion engine, the latter should be taxed according to the emissions they produce.

However, it’s come to light that Volkswagen – and several other motor manufacturers – apparently utilised software produced by ECU manufacturers for ‘test purposes only’, so that CO2 production would be artificially lowered during the emissions-testing process.

CO2 emissions data is scarce

Almost all motorhomes are built on a light commercial vehicle chassis, be it Fiat’s Ducato, Citroën’s Relay, Peugeot’s Boxer, Mercedes’ Sprinter or even the good old Transit from Ford. As far as I’m aware, CO2 emissions data is only just coming into play for these vehicles, so the falsified-claims issue is unlikely to be applicable.

If you’re buying a new motorhome any time soon, the best course of action would probably be to look closely at the paperwork and spec sheets for your proposed purchase, then ask the selling dealer to confirm that the figures are correct.

No impact on tax – yet

But will the CO2 levels make any real difference to you? Not yet, it seems: I’ve just looked on the Government website for road tax rates, and so far light commercials are still listed according to their gross vehicle weight class: ie, up to 3500kg (Private Light Goods) and over 3500kg (Private Heavy Goods).

At the moment, diesel emissions are only checked for ‘visible smoke’ during their MoT; this is confirmed with a calibrated-meter reading. CO2 isn’t currently tested during the MoT on diesel-engined vehicles; however, bear in mind that it might be added to the test procedure in future. I seriously doubt whether any remapped or chipped diesel engine will pass when CO2 output is finally monitored!


A keen motorcaravanner, Practical Motorhome's technical expert Diamond Dave runs his own leisure vehicle workshop. Find out more at Dave Newell Leisure Vehicle Services.

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