Road safety police pulled over the Victorian-registered car on Vernon Circle and immediately spotted faults in the heavily modified vehicle.

Police slapped an immediate defect notice on the car and took it to the Road Transport Authority inspection station in Dickson.

Inspectors discovered the car had a cracked chassis rail and an engine mounting that had completely broken away, putting pressure on the steering arm and other components.

Important retaining bolts fitted to the engine also had very little engagement.

Acting Superintendent Rod Anderson, from ACT Policing's Traffic Operations, said the likelihood of "impending failure" at speed was very high.

Mr Anderson said it posed a "huge risk" to the safety of anyone in the car or nearby.

"It's hard to believe that anyone would risk driving a vehicle with faults as significant as these," he said.

"This car was a catastrophe waiting to happen.

"It was fortunate that our officers were able to prevent it driving any further than necessary and it was able to be fully inspected by the RTA."

The hotrod was not entered at Summernats, and ACT authorities have advised their Victorian counterparts about the inspection.