Almost a quarter of the region's ambulances were broken down at some stage in July according to new data, which a union chair has said "raises alarm bells".
Between July 1 and July 31, some 113 separate breakdowns were recorded by the East of England Ambulance Service Trust (EEAST), which has a total fleet of 489 dual-staffed ambulances.
A Freedom of Information request revealed that of these, 103 breakdowns were recorded amongst Fiat model ambulances which were introduced just four years ago following a £54m deal, and now make up 442 of the trust's vehicles.
The remaining 10 breakdowns were amongst Mercedes model ambulances, which remain in the fleet from before the Fiat Ducatos were introduced.
While the East of England Ambulance Service Trust said it has seen a higher-than-average demand for maintenance for a variety of reasons, including global supply chain issues, Glenn Carrington, UNISON union's East of England Ambulance Service branch chair, said the statistics are alarming.
"It’s always worrying to hear that ambulances are off the roads and for a quarter of vehicles to be sidelined in a month raises alarm bells," said Mr Carrington.
"We’re already stretched in terms of funding and staff numbers, failing vehicles are a headache ambulance staff just don’t need.
"However, we understand that the new Fiats have generally sped up routine maintenance and technicians are always working hard to get vehicles out of the garage again.
"Crews want to be out on the road helping patients, not stuck dealing with mechanical faults."
An East of England Ambulance Service spokesperson said: "We have nearly 500 ambulances within our fleet serving patients across the East of England.
"These vehicles cover thousands of miles in service and are taken off the road for scheduled maintenance and repair when required.
"We have seen a higher-than-average demand for maintenance this summer due to a combination of causes, including global supply chain issues.
"Fiats represent 90% of our fleet and are not over represented of vehicles requiring maintenance."
The move to bring in the newer Fiat Ducato ambulances, which were introduced to the region in 2019, was a controversial one as almost 100 ambulance workers suffered problems when driving the new fleet due to height and body shape.
In 2022, figures revealed that following the introduction of the £54m converted Fiat vans by the East of England Ambulance Service Trust, 94 members of staff were identified as being unable to drive them.
The issues with the Fiat vehicles affected taller members of staff, with crammed-in drivers suffering from back pains, restricted vision out of the windscreen and scraped knees and shins on dashboards.
There were also some complaints that the pedals on the vehicles were too close together for drivers wearing work boots to safely operate them.
The trust was also required to roll out training on safe use of sliding doors on the ambulances, after a member of staff got their hand trapped resulting in two broken fingers.
Of the East of England fleet, the Fiats range from 2019 to 2021, therefore are between two and four years old, while the Mercedes vehicles are 2016 and 2018 models, therefore five to seven years old.
The modified Fiat Ducatos have been rolled out across the country, with other services including West Midland Ambulance Service and the North West Ambulance Service also introducing them.
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