The crash occurred on State Highway 1 near the intersection with SH83 at Pukeuri about 1.30pm on Saturday.
The ambulance was rolled on to its side and the road blocked for hours.
The crash was between an ambulance and an unmarked manager’s vehicle, Senior Sergeant Anthony Bond, of Dunedin, said.
The ambulance was being driven by an on-duty ambulance officer, carrying another on-duty officer as a passenger.
The manager’s vehicle was being driven by an off-duty employee.
The investigation found the driver of the ambulance was at fault. They were issued a written traffic warning for failing to give way, Snr Sgt Bond said.
All three had minor injuries and one was taken to Timaru Hospital for treatment.
When asked earlier in the week if the crash was between two St John vehicles, St John refused to comment, saying it was in the hands of the police.
Following the results of the police investigation, St John rural Otago territory manager David Milne said it was conducting its own investigation into the incident.
St John could not comment on individual employment matters, he said.
