Buying a used car has always involved an element of trust. But new research suggests some motorists may be less forthcoming than buyers would hope, particularly when expensive mechanical repairs are involved.
A survey of 2,000 UK car owners, conducted by research company OnePoll on behalf of vehicle diagnostics specialist Carly, found that around one in 12 respondents would not voluntarily disclose an expensive fault when selling their car.
Five per cent admitted they would only reveal the problem if specifically asked, while a further 3% said they would remain silent altogether.
The findings raise an important question for anyone considering a second-hand vehicle: how much can you really discover about a car before handing over your money?
Younger sellers appear less willing to disclose faults
According to the Carly research, the willingness to disclose expensive faults varies considerably between age groups.
Among car owners aged 35 to 44, 15% said they would either keep quiet about an expensive repair or reveal it only when questioned.
That compares with just 3% of respondents aged 65 and over.
The geographical findings also revealed differences in attitudes. Wales recorded the highest proportion of respondents prepared to withhold information, at 13%, followed by London at 12%.
Car owners in the South West appeared more willing to be upfront, with only 5% saying they would conceal a fault or wait to be questioned.
These regional figures should be treated as survey indications rather than definitive measures of seller behaviour. The research excluded Northern Ireland and the North East from its regional comparisons because their sample sizes were below 80.
Nearly half would repair the problem or reduce the price
There is a more encouraging side to the findings.
Almost half of those surveyed indicated they would take positive steps to address an expensive fault before completing a sale.
- 25% would disclose the problem and reduce the asking price.
- 24% would arrange for the fault to be repaired before selling.
Together, these groups account for 49% of respondents.
For used-car buyers, this underlines the importance of asking direct questions about a vehicle’s condition and checking whether any previous faults have been properly repaired.
It also highlights the value of service records, repair invoices and independent vehicle inspections.
Could diagnostic reports become standard when buying a used car?
Carly believes vehicle diagnostics should play a much bigger role in used-car transactions.
The company is calling for a diagnostic health report to become a routine part of the sales process, presented alongside a vehicle’s MoT history, service records and V5C registration document.
Modern cars contain numerous electronic control systems capable of recording faults that may not be immediately obvious during a visual inspection or short test drive.
Some diagnostic trouble codes can remain stored even when no dashboard warning light is illuminated.
Carly argues that providing a diagnostic report would allow buyers to make better-informed decisions while helping responsible sellers demonstrate that they have nothing to conceal.
The company offers an OBD2 scanner and accompanying smartphone app, enabling motorists to access diagnostic information through a vehicle’s onboard diagnostic port.
However, a diagnostic scan is not a substitute for a comprehensive mechanical inspection. Not every fault generates an electronic code, and some stored codes may relate to historic problems that have already been resolved.
What does Carly say about the research?
Dali Ati, Head of Internationalisation at Carly, said:
“This isn’t about suggesting every used car has a hidden problem. It’s about bringing more transparency and trust to buying and selling a car, so both sides can shake hands on a deal with confidence.”
The proposal also reflects Carly’s commercial interest in promoting diagnostic checks, although the broader principle of providing buyers with more information has clear consumer benefits.
Five ways to buy or sell a used car with greater confidence
The research is accompanied by five recommendations from Carly, which Motoring Echo has adapted into practical advice for motorists.
1. Ask about faults before agreeing a purchase
Ask the seller directly whether the vehicle has any known mechanical or electrical problems, warning lights or outstanding repairs.
Request written confirmation of any important statements about the car’s condition.
2. Don’t rely entirely on dashboard warning lights
A dashboard without warning lights does not necessarily mean the vehicle is fault-free.
A diagnostic scan can reveal stored trouble codes, although results need to be interpreted correctly and should be considered alongside a physical inspection.
3. Check the vehicle’s MoT history
The government’s free online MoT history service can reveal previous test failures, advisory notices and recorded mileage.
Repeated advisories or unexplained mileage discrepancies should prompt further investigation.
Buyers can access the official service at GOV.UK – Check MoT history.
4. Check your own car before advertising it
For sellers, identifying potential problems before advertising a vehicle can help avoid disagreements later.
Faults can then be repaired or clearly disclosed, with the asking price adjusted where appropriate.
5. Provide supporting documentation
A recent diagnostic report, service history and repair invoices can provide useful evidence of a vehicle’s maintenance and condition.
For buyers, these records should complement rather than replace a test drive, vehicle history checks and, where appropriate, an independent inspection.
What does the Carly diagnostic system cost?
Carly’s diagnostic system combines an OBD2 scanner with a smartphone application.
The company offers Basic and Premium packages, with pricing stated in its supplied information as starting at approximately £40.
Actual costs and available diagnostic functions can vary according to the vehicle, package and any applicable subscription.
The Motoring Echo Verdict
The used-car market depends heavily on confidence, and that confidence can quickly disappear when an expensive fault emerges shortly after purchase.
Carly’s research suggests that a minority of motorists would be prepared to withhold important information when selling their vehicles. Equally, the findings show that many owners would prefer to repair a problem or reflect it in the selling price.
Making diagnostic reports more widely available is an interesting proposal, particularly as modern vehicles become increasingly dependent on sophisticated electronics.
Nevertheless, a diagnostic report is only one part of the picture. Mechanical condition, maintenance history, accident damage and previous repairs remain equally important.
For Motoring Echo, the message is straightforward: ask questions, examine the paperwork and never rely solely on a seller’s assurances.
An independent inspection before purchase can prove considerably less expensive than discovering a major fault afterwards.
Research source and methodology
Source: Carly, vehicle diagnostics specialist. Research conducted by OnePoll on behalf of Carly, involving 2,000 UK car owners.
Respondents were asked how they would be most likely to act if they wanted to sell their car while knowing it had a fault that felt very expensive to repair. Regional findings exclude the North East and Northern Ireland, where samples contained fewer than 80 respondents.
The figures describe respondents’ stated intentions in a hypothetical situation, not independently verified instances of faults being concealed during actual vehicle sales.
