If you’re planning on purchasing a car, a pre-purchase inspection is a useful service that’ll help you avoid any nasty surprises. Part of the inspection involves checking mechanical and electrical systems – so what happens if the anti-lock braking system (ABS) light is on?
Here, we’ll explore what a report will show if the ABS light is illuminated – and what the light could be telling you about the car you’re potentially buying.
What is an ABS warning light?
When you start your car, a variety of warning lights flash up for a couple of seconds as the car checks everything is working correctly. Your anti-lock braking system light is one of these.
The ABS light is easy to spot. In most cars, it’ll flash up in the cluster of dials you have behind your steering wheel. It’s usually an amber light, and it’ll have the letters ‘ABS’ in the middle of a circle. Around that circle, there’s another circle – but this outer circle’s got the top and bottom chopped off; leaving semi-circles on the left and right.
If your ABS light stays on when you start your car – or it comes on suddenly when you’re driving, it’s telling you there’s a problem with the braking system.
What does ABS do?
An anti-lock brake system is a safety feature that’s designed to stop a car skidding. If you’ve ever had to press your brake pedal to stop yourself quickly – you may have felt it; it’s a quick pulsating feeling through the pedal that usually causes the car to judder as it slows.
This juddering occurs because the brakes are not simply locking up. If they were, the tyres would lose grip and the car would slide – usually out of control. So the car doesn’t lose control and skid like this, the brakes grab very quickly then release again – around 15 times per second. Since the wheels don’t lock-up, the car comes to a more controlled halt.
ABS has been a legal requirement on vehicles since 2004 – and an ABS warning light that’s permanently on means your car will fail an MOT.
Will the car pass an inspection if the ABS warning light is on?
Although a vehicle will fail an MOT if the ABS warning light is on, it won’t fail a vehicle inspection – since an inspection isn’t designed to be a pass/fail exercise.
Instead, you’ll get a detailed reporting that tells you that there’s a warning light showing – as well as a diagnostic report that goes into detail about why the light is on.
Our reports are designed to make spotting problems with a car as easy as possible. Throughout the inspection and road test, the inspector will mark each part of the car as either ‘OK’ (green), ‘Warning’ (amber), ‘Danger’ (red), or ‘N/A’ (grey). Since the warning lights cannot be seen until the car is started, an illuminated ABS light would show in the Road Test section of the report and would be flagged as red for ‘Danger’.
What could an ABS warning light mean?
There’s no single reason an ABS warning light will come on. Ultimately, it means that there’s a problem with the system and the system has been deactivated – but it could be for a number of reasons.
Common reasons your ABS light will show include:
Low braking fluid
Your braking system is activated using hydraulic fluid. If the fluid level is too low, it may mean there’s not enough pressure in the system to apply the brakes as needed. Even a little leak can mean pressure drops off quickly – and if it does, the ABS light will let you know.
Faulty speed sensors
Each individual brake on your vehicle has a sensor built into it. This sensor is designed to report back to the ABS control module and tell it if the wheel has locked. Since this is an anti-lock system, this means the control module can apply and release the brakes as needed – but a faulty sensor means this can’t happen – so the ABS light will come on to let you know.
Faulty control module
While the speed sensors work out how quickly each wheel is turning, it’s the control module that decides how much braking pressure is needed on each wheel to reduce your speed safely. If there’s a problem with this module (often corrosion or damaged electrical connections), then the ABS light will come on.
A pump problem
So, speed sensors tell the control module if there’s a problem – but this module relies on a hydraulic pump to actually apply and release the brakes. The trouble is, hydraulic pumps tend to wear out after years of use – so if yours has seen better days, it’ll cause the ABS light to come on to warn you.
Since your braking system is electronically controlled, any problems will create a ‘fault code’ – a record of issues that are stored on the Engine Control Unit (ECU) in your car.
Our inspector will check these fault codes and list them on your pre-purchase report. There are hundreds of potential codes for each vehicle – but with the right equipment, a garage can quickly pinpoint the issue and let you know the parts and labour involved with putting it right.
Should you buy a car that’s got an ABS warning light showing?
Ultimately, a pre-inspection report is designed to give you all the information you need to decide if a car’s going to be right for you. Since an ABS warning light could mean different things, whether or not you buy the car is up to you.
As an ABS warning light would mean an MOT failure for the car, you shouldn’t drive it when the light’s on. Instead, you should seek the advice of a mechanic who’ll be able to give you a price for fixing the issue. Chances are, you’ll also need to have the vehicle collected on a trailer; since it’s unlikely to be safe to drive on the road.
There’s a lot to consider when there’s a warning light on in a car you’re hoping to buy. Do you have the knowledge and skills to fix the problem yourself? Does the price of the car represent a good deal – even if it means a trip to the garage before you can drive it?
There are a lot of questions to ask – but one thing’s for sure, a pre-inspection report is money well spent if it alerts you to a dangerous ABS issue you might have otherwise missed.