A police officer investigating a Taranaki crash involving an off-duty officer had a conflict of interest and his investigation was "substandard", the police watchdog has found.
In November 2015, the off-duty policeman overtook a truck on a country road, forcing an oncoming driver to swerve off the road.
The woman suffered minor injures and her car was damaged.
The investigating officer decided to issue the off-duty officer with a written warning, rather than prosecuting him, as long as he paid the woman reparation.
The woman complained to the Independent Police Conduct Authority in March last year, saying police were treating the officer more favourably than they would an ordinary member of the public.