Two police officers ended up in hospital after being poisoned by fumes from a patrol car.
An internal probe has been launched after the pair fell ill last weekend.
They had been working night shift together in a BMW X5 before becoming unwell.
An ambulance was called to take the officers from Glasgow’s Govan station to the Queen Elizabeth University Hospital.
Doctors treated the pair for suspected carbon monoxide poisoning and admitted them to a ward overnight.
Police union leaders described last Sunday’s incident as “very concerning”. The vehicle was taken off the road for tests to discover the problem.
It comes amid ongoing concern about the safety of Police Scotland’s ageing fleet of patrol cars.
Last October, it was revealed the Scottish Police Authority had budgeted £7million to pay for repairs.
Officers have previously complained to the Scottish Government that some police vehicles are held together with cable ties and patched up with duct tape.
A source said: “Carbon monoxide poisoning shows the problems officers are facing in some of the cars they have to drive.
"You used to have to check for carbon monoxide when stopping a suspected drunk driver as it could have been the reason for them driving erratically. But that is going back 20 years.
“Some patrol cars have more than hundreds of thousands of miles on the clock and officers are concerned about the state of the fleet.”
Engines produce poisonous carbon monoxide when fuel is burned.
But the deadly gas is converted into non-toxic carbon dioxide in modern exhaust systems. However, a leak in the exhaust system can see carbon monoxide escape and enter cars through open windows or doors.
The gas is scentless and prevents blood cells carrying oxygen.
High levels can kill within five minutes.
The Scottish Police Federation, which represents frontline officers, said similar problems have occurred “three or four times in the last seven years”.
General secretary Calum Steele added: “This is very concerning and could have had tragic circumstances.
“We need an immediate investigation into the circumstances to establish the facts for the benefit of all officers who use these vehicles.”
Chief Superintendent Louise Blakelock, head of road policing, said: “At about 5am on Sunday, January 17, 2021, two road policing officers were taken to the Queen Elizabeth University Hospital, Glasgow, after becoming unwell during their shift.
“It was established the officers had suffered carbon monoxide poisoning while within their police vehicle, a BMW X5. The vehicle was examined and an investigation into the cause is ongoing.
“The vehicle has been removed from the fleet until the investigation is complete. Other BMW X5s in the fleet have been checked.
"This has been an isolated incident and had no impact on our ability to provide a policing service.
“Both officers were taken to hospital for treatment and have since been discharged. The health and safety of all our officers and staff is paramount to Police Scotland.”
Scottish Conservative justice spokesman Liam Kerr said: “I wish these officers a full and speedy recovery. Police Scotland must investigate how this happened to ensure there is no repeat.”