An Garda Síochána is carrying out just half the number of drink driving breath tests that it claims to, the force has said.
Almost two million tests were recorded by gardaí between 2012 and 2016 but it has now said less than a million were actually carried out.
The controversy was first reported in The Irish Times last month and within days the Policing Authority expressed concern it had not been told about it.
The reported discrepancy led to concerns that gardaí across the State might have been fabricating tests to give the impression road traffic enforcement is much higher than it actually is.
However, when revealing the scale of the discrepancies on Thursday, Assistant Commissioner Michael Finn denied the Garda was only releasing the information now because it had been published in the press.
Mr Finn, who has responsibility for road policing, said the Garda had gone to the Medical Road Safety Bureau of its own volition when it became concerned the figures were wrong over a year ago.
However, he said the Garda did not know why the figures were so wrong. He insisted procedures had been changed to ensure it could not happen again.
Mr Finn said all details of when a test was carried out and by whom would be automatically recorded on Pulse from the roadside.
The force has taken its breath test figures off the Garda database and said it would wait to begin publishing them until it was certain the figures were now being recorded correctly.
The Garda compared its data to figures compiled by the Medical Road Safety Bureau, which calibrates the testing kits for the Garda.
Between 2012 and 2016 its calibration activity suggests 1,058,157 tests were carried out but the Garda records, on its database, recorded 1,995,366 tests.
The Garda has also apologised after 14,700 motorists who were summoned to court and convicted without being given the opportunity to pay a fine first under the fixed charged notice system.
The Garda must now go to the courts and appeal all of the convictions in a process that will likely take years and costs tens of millions of euro.
Mr Finn said because of the possible costs and legal claims that could be taken against the State by those affected by the issue, the State Claims Agency had been informed.