The information was revealed in internal police documents released under parliamentary order to Greens MP Sue Higginson, who said the revelations highlighted a "culture of impunity" within the state's police.
A form, provided when an insurance claim for the crash was lodged by the officer, said the May crash happened while the car was travelling north through Sydney's NorthConnex tunnel and the driver "fell asleep".
"Vehicle veered off roadway, colliding with a crash cushion," the form said.
"Vehicle was still driveable so vehicle driven from scene."
Officers investigating the incident later told the insurance company the driver had been drinking alcohol before the crash and the damages claim, worth $40,955, was refused, emails showed.
The high-ranking detective had allegedly been drinking at a function before getting behind the wheel of his police-issued car in the lead-up to the incident.
His identity cannot be revealed for the next 40 years due to a court non-publication order.
Another senior officer expressed his concern about the insurance form in a September email, in which he noted the document included no mention of alcohol.
"In my view the claim in (its) current form is one submitted in bad faith," he said, noting that the detective had been told two months earlier that charges were likely.
"For (NSW Police) to continue with this claim without disclosing these facts is likely to cause significant reputational damage to the organisation as well as breaching (insurance laws)."
It was not until November - six months after the crash - that the detective was charged with driving with a blood-alcohol level of more than 0.15, or more than three times the legal limit.
The high-range drink-driving charge carries a maximum jail term of 18 months.
The matter has been referred to the internal Professional Standards Command and the independent police watchdog, the Law Enforcement Conduct Commission.
The officer's employment status is under review.
Ms Higginson has been calling for an independent inquiry into the incident, saying the police commission was limited by its powers and resources.
"We want accountability on this culture of impunity and cover up," she told AAP on Friday.
NSW Police Commissioner Karen Webb previously said she had been aware of the incident since May and the officer had been charged after a "lengthy and comprehensive" investigation.
She denied there had been any attempt to cover up the allegations in the failure to issue a public statement outlining the charges, describing it instead as something that "slipped through the cracks".
But Ms Higginson said the public deserved better from the state's police and integrity and accountability needed to be of utmost importance.
"It's not been a great year for NSW Police ... there is a building mountain of police problems," she said.
The accused officer is due to appear in court next week and NSW Police said it would be inappropriate to comment while the case was still pending.
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