We checked five cars using the £1.99 service which we knew had been in accidents and classified as Category C or Category D by insurers - and all of them came back as not having been written off by TotalCarCheck.com, despite their dangerous hidden history.
The website promises to tell buyers if their used car has been scrapped, changed colour or written off. But our investigation found there are catastrophic holes in the data it returns to consumers.
"This is shocking," said The AA's Ian Crowder. "We absolutely condemn this kind of practice - it potentially places unwitting car buyers in a dangerous situation.
"They could end up buying a vehicle that has previously been in an accident or is otherwise in an unroadworthy condition."
The Institute of Advanced Motorists was similarly disgusted at our findings. Spokesman Tim Shallcross said: "Used car sales amount to billions every year and that money tempts many to try their luck in almost every sector of the motor trade, as in this case AOL has exposed, a firm charging people for virtually worthless information."
Thousands of these online look ups, dubbed "provenance checks", take place every day but most firms offer a very good service. Well known brands such as HPI, The AA and RAC all offer services to motorists that can help them delve into their next used car's past with confidence.
We contacted TotalCarCheck.com and it said our investigation had highlighted "flaws" in its service. It blamed data that it was provided from outside agencies was at the root of the cause.
A spokesman for the company told us: "I one hundred per cent recognise there are errors with the data and we are trying to get to the bottom of it.
"We are aware that there are data quality issues and we are working with the head of the police national computer and the motor insurance bureau to resolve them."
However, the company refused to pull the service immediately or warn suspecting customers that the data it produced may not be accurate.
"If we can't resolve these issues within the next week or so we may suspend sales activity on the site, though I can't be definitive on that right now."
AOL Cars has since handed over its findings to Trading Standards.