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Pre-purchase vehicle inspection

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We’re certain we provide the best pre-purchase used car inspection service in the UK. Our service leaves no part of the vehicle’s condition or history in doubt.

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Will a vehicle pass an inspection with the check engine light on?

A pre-purchase vehicle inspection is a great way to make sure you’re buying your next vehicle with confidence. As well as checking the mechanical and cosmetic condition of the vehicle, electrics will also be reported on – so, what happens if the engine warning light is on?

Here, we’ll look at what impact an engine warning light will have on a vehicle inspection, as well as what it could mean for the health of the car you’re looking to purchase.

What is a ‘check engine’ light?

If you’re a driver, you’ll see your engine management light come on every time you start your car. It’s an amber coloured light that looks roughly like the rectangular outline of an engine that’s found behind the steering wheel, in your instrument cluster. Don’t worry though, like your oil or airbag warning light, it generally only lights up for a couple of seconds when you switch the electrics in your car on – then goes off.

That said, sometimes your engine warning light will stay on or may come on when you’re driving – sometimes to alert you to a serious problem with the car, and sometimes just because of a minor fault.
Since your engine warning light can come on for a variety of reasons, having one showing on a car that you’re thinking about buying is a cause for concern.

What does the engine warning light mean?

There’s no single reason that your engine management light will come on. In actual fact, the light is connected to your car’s ‘Engine Control Unit’ – or ECU. The ECU is the ‘brain’ of the car, a computer that manages everything from fuel to braking systems. Since the ECU controls so many different things – there’s a long list of potential problems that an engine warning light could be telling you.

This long list of potential problems can only really be explored in more detail with specialist computer software. Fortunately, dealers, garages, and our inspectors carry this diagnostic equipment. When a laptop with the appropriate software is connected to your car, it will read ‘fault codes’ that are registered on the ECU. Each of these fault codes indicates a different problem – some are easily fixed – but others can represent really big problems.

What are some common reasons for the engine management light staying on?

There are often hundreds of potential problems that your engine warning light could be trying to alert you to – but there are a handful of common issues that come up for many manufacturers. They include:

Mass airflow sensor problems

The mass airflow (MAF) sensor analyses a range of conditions and decides how much fuel and air your engine needs run as efficiently as possible. If there’s a problem with the sensor, your fuel/air balance can be incorrect, causing the car to run poorly – or even switch into ‘limp mode’ meaning the car will not move at more than a few miles per hour.

A MAF problem will usually show up as an engine warning light on your dash.

Ignition system problems

Although the system is slightly different between petrol and diesel vehicles, at some point, engines need either heat or a spark to ignite the fuel/air mix and get the engine running. When there’s a problem with this system, the car will either struggle to start or might ‘misfire’ – meaning power is lacking or intermittently drops off. 
Problems with this ignition system generally show up as an amber engine warning light.

A fuel tank issue

You might not realise it, but your fuel tank ‘breathes’. As fuel leaves and is used by the engine, it’s replaced with air – so that a constant pressure is maintained and the sensors that decide how much fuel is drawn into the engine can keep the system running properly. 

If the pressure in the tank is slightly wrong, the ECU will consider there to be a fuel problem, and the engine warning light will show up again. 

DPF problems

On diesel cars, a DPF (diesel particulate filter) removes dangerous particles from exhaust gases. After a while, this filter can become clogged up with a sooty residue – and the engine will deal with this by periodically burning a little extra fuel to increase the pressure on the DPF and burn the soot off. 

The problem is, this heat build-up requires the car to run for ten or more minutes – and that simply might not happen if you rarely do more than a few miles. As such, this DPF can become more and more blocked up – meaning the engine struggles to vent exhaust gases as it should. The result? The engine warning light will often come on.

Emissions system faults

Throughout your exhaust system, there are sensors that monitor the amount of oxygen that’s released after combustion has taken place in the engine. Too much oxygen would indicate to the ECU that the air/fuel mix is incorrect.
An incorrect fuel mixture would be enough to trigger the engine warning light – but, as is more often the case, so would a broken oxygen sensor that’s providing an incorrect reading. Either way – the engine management light will come on.

What will an inspection report say if the engine management light is on?

Since a pre-purchase inspection isn’t designed to ‘pass’ or ‘fail’ a vehicle, it will simply show if there are any engine management issues with the car – and, if so, what they are.

In the Road Test section of the report, there is a line that indicates whether the Warning Message/Light is showing. If it isn’t, this will be marked as ‘OK’ (green). If the light is showing, it will be marked as either ‘Warning’ (amber) or ‘Danger’ (red) – depending on the reason it’s come on.

In the Diagnostics section of the report, any fault codes registered on the ECU will show – and, if the engine warning light is on, you can expect to see why here. The code will be shown, as well as which system the code relates to, and a description of the problem it indicates.

Again, none of this information will ‘fail’ a car as such – but it is likely to be cause for concern, and gives you all the information you need to decide whether it’s a problem you’re willing to take on with your new car – or whether it’s time to look elsewhere.

Other related FAQs

Looking for more related content to this? We’ve picked a selection of related topics that you may find helpful

With Car.co.uk, you don’t need to be present when one of our independent inspectors carries out an inspection on your behalf. Your report will include photos of the car too – so you can be confident you’re getting the full picture, even if you’re miles away.

A pre-purchase vehicle inspection is a way of checking the overall condition of a car you’re looking at buying. The inspection report that’s produced will help you discover any hidden issues with that car before you part with any money.

At Car.co.uk, there is no maximum age for Premium Plus vehicle inspections. However, we have a 10-year age limit for our Premium inspection service.

At Car.co.uk, we do not provide pre-purchase inspections for motorcycles. However, the independent vehicle inspectors we work with can inspect a huge range of vehicles, from cars to motorhomes, and almost everything in-between.

A vehicle inspection report is a document created when an independent professional carries out an inspection on a pre-owned car. The report tells you everything you need to know about the condition of the vehicle and any hidden issues it might have.

Vehicle inspections are designed to give you all the information you need to decide whether or not a car is right for you. An independent inspector will check the electrical, mechanical, and cosmetic parts of a vehicle; before providing you with a detailed report on their condition.

The cost of a pre-purchase vehicle inspection will start from either £189 or £229 – depending on the level you choose. Your inspection will be promptly carried out by a professional vehicle inspector, and you’ll receive a detailed photographic report about the car.

Currently, we can only inspect vehicles up to 3.5 tonnes in gross vehicle weight. The good news is, this covers virtually all standard cars on the road today – even luxury vehicles with large engines.

The cost of a vehicle inspection through Car.co.uk starts at £189. When you consider that around 50% of pre-owned vehicles currently for sale have some undeclared damage or negative history, this is a small price to pay to know you’re buying an honest car.

A pre-purchase vehicle report is based on the expertise and opinion of the inspector at the time the inspection is carried out. Since we cannot control what happens to the vehicle after the report is completed, an inspection does not come with a guarantee.