How to Check Dashboard Warning Lights Before Buying a Used Car

Dashboard warning lights are one of the quickest ways to spot a possible problem when viewing a used car. They can indicate anything from a routine system status to a fault affecting the engine, brakes, airbags or electrical systems.

Knowing how to check dashboard warning lights before buying a used car does not require specialist equipment. You can carry out a few sensible observations during the viewing, then ask for further checks if something does not look right. Warning lights should not be considered in isolation, however. The vehicle’s service history, condition, MOT history and road test all matter as well.

For a broader inspection guide, see our article on what to check when buying a used car.

Check the warning lights before the engine starts

Ask the seller if you can see the car with the ignition switched on but the engine not yet running. On many vehicles, a number of dashboard lights should illuminate briefly as part of the vehicle’s self-check. This may include the engine management, oil pressure, battery, ABS, airbag and seat belt warning lights, depending on the model.

This initial display is useful because it shows that the warning system is operating. Once the engine is started, many of the lights should go out after a short period. The exact sequence varies between manufacturers, so use the owner’s handbook to confirm what is normal for that particular car.

Do not assume that a completely clear dashboard is automatically good news. If an important warning light never appears during the ignition self-check, it could be worth asking why. A failed bulb or LED, a disabled warning system or a previous attempt to hide a fault are all possibilities. You cannot confirm the cause just by looking, but it is a reason to seek more information.

Understand the basic warning-light colours

Colours provide a useful first indication, although the symbol and the owner’s handbook are more important than colour alone.

• Red lights commonly indicate a serious warning or a condition needing immediate attention. Examples may include low oil pressure, high coolant temperature, a brake system warning or a charging fault.
• Amber or yellow lights often indicate a fault or system that needs checking soon. Examples can include the engine management light, ABS, tyre pressure monitoring or a diesel particulate filter warning.
• Green or blue lights are usually status indicators, such as headlights, cruise control or a cold-engine temperature indication. They are generally not fault warnings, but the handbook remains the best reference.

A red warning light does not always identify the precise failed component. It tells you that the vehicle may need attention, not that you can safely diagnose the problem at the roadside. If a red oil pressure, brake or overheating warning remains on after starting, the safest course is not to continue driving the car until it has been properly assessed.

Watch what happens after the engine starts

Start the engine yourself if the seller agrees, and look at the dashboard once it is running. Some lights may take a few seconds to go out. Turn the steering wheel gently, release the handbrake correctly and allow the car’s normal checks to complete, without carrying out any repairs or dismantling.

Pay particular attention to warning lights that:

• Stay on continuously after the engine has started.
• Appear only after the car begins moving.
• Flash rather than remain illuminated.
• Come on intermittently during the viewing or road test.
• Disappear when the dashboard is reset but return later.

An intermittent light still matters. A fault may depend on temperature, speed, battery voltage or a particular driving condition. A seller may describe it as a minor issue, but it is reasonable to ask for the exact fault to be investigated rather than accepting a vague explanation.

Look for warning signs that have been hidden

Some vehicles have warning lights that have been reset after a fault was stored in the vehicle’s computers. This may make the dashboard look clear temporarily, but the light can return after the car has been driven through its normal checks.

Ask when the warning light was last present, what caused it and whether any work was completed. Request invoices or other supporting records where available. Be cautious if the seller cannot explain a warning, says that it has only just been cleared or will not allow a proper road test.

You should also compare the dashboard with the owner’s handbook. A missing symbol during the ignition self-check is not proof of tampering, as some vehicles display systems differently. It is simply a prompt to ask questions and, if necessary, arrange an independent inspection.

Do not ignore safety-related warning lights

Some dashboard warnings relate directly to roadworthiness. A brake warning, ABS warning, airbag warning, steering warning or overheating warning deserves more than a casual explanation.

If the brake pedal feels soft, the steering feels unusually heavy, the engine temperature rises, smoke appears or the vehicle behaves unpredictably, do not continue with the road test. Stop in a safe place and seek professional advice. It is not sensible to buy a car with a safety-related warning on the assumption that the repair will be simple.

Even where the car drives normally, a warning light may indicate a fault that has not yet caused noticeable symptoms. This is particularly relevant to airbags, electronic stability systems and engine management. Ask a garage to inspect the vehicle before you commit to the purchase if the warning cannot be explained clearly.

Ask for a proper diagnostic check

A diagnostic scan can identify fault codes stored by the vehicle’s control systems. It can be helpful, but a code is not always a complete diagnosis. It may point towards a system or circuit that still needs physical testing.

Do not treat a clean scan as a guarantee that the car is fault-free. Some faults may not be active at the time of the check, and some problems are mechanical rather than electronic. A proper pre-purchase inspection should consider the dashboard, engine bay, tyres, brakes, suspension, bodywork and service records as a whole.

Our guide to what service history a used car should have explains why records can be just as useful as the dashboard when judging how a vehicle has been maintained.

Use the warning lights alongside the car’s history

Warning lights are only one part of the buying decision. Check that the mileage, servicing and repair records make sense together. A warning that appeared shortly after recent work may need a different investigation from one that has been present for months.

It is also worth asking whether the vehicle has had a recent battery replacement, as low voltage can sometimes trigger multiple electronic warnings. That does not mean the battery is necessarily the cause, so avoid accepting a quick explanation without evidence.

For more detail on the paperwork itself, read what a vehicle service book is. If you are considering an older car, our guide to how much maintenance an older car may need can help you plan for ongoing ownership costs.

When should you walk away?

There is no single dashboard light that automatically means a car must be rejected. The important questions are whether the warning is understood, whether the seller is open about it and whether the likely repair has been assessed properly.

Be prepared to pause or walk away when a serious warning remains on, the seller refuses an independent inspection, the dashboard does not behave as expected or the explanation does not match the vehicle’s symptoms. A lower purchase price does not remove the safety risk or guarantee that the eventual repair will be affordable.

If you are unsure about a car you are considering, Ashton’s Garage can carry out a vehicle inspection and discuss any warning lights found during the checks. You can find the relevant vehicle servicing information for Salisbury and decide whether a professional assessment is worthwhile before completing the purchase.