Emergency staff sent two Northamptonshire ambulances eight miles in the wrong direction.
Controllers meant to dispatch a crew from Duston, Northampton, to a crash five miles north in East Haddon.
But they entered the wrong "zone" in the sat-nav equipment and the crew travelled south to Collingtree instead.
When the crew arrived at the wrong place they alerted staff. A second crew was sent to the wrong site, but spotted the error in time to change route.
They eventually reached the scene of the two-car collision, which was reported at 1950 BST on 21 August.
One casualty was taken to Northampton General Hospital with minor injuries.
The mix-up has been blamed on human error by senior East Midlands Ambulance Service (EMAS) staff.
A spokesman said: "We have established that an incorrect 'zone' was entered against this booking by an operator.
"This led to the first back-up vehicle being directed towards Collingtree.
"The crew of the second back-up vehicle received the same information, but the error was recognised and they were able to divert to the correct location."
The EMAS pointed out that a paramedic had already arrived at the site before the ambulance was called in.