The variable signs thank motorists with a smiley face but tell them to slow down if they are going too fast.
The sign displaying the wrong speed was installed by the Ashburton District Council in a 70km/h zone on Seafield Rd near Ashburton Airport last week.
But it has been telling motorists to slow down to 50km/h.
The district council corrected the sign after The Ashburton Courier informed it about the anomaly on Monday.
It was at least the second time one of the variable signs at the same Seafield Rd location has shown the wrong speed.
The Ashburton Courier ran a story in October 2023 about the same thing happening.
Council group manager of infrastructure and open spaces Neil McCann said the error this time was caused by a technology issue.
"The signs are mobile and once the contractor moves them, they email council to update the speed message if it is being moved to a location with a different speed limit.
"This is usually done successfully by remote access but like all technology, sometimes there are connectivity issues and they need to be reset onsite," McCann said.
He said the sign was one of two mobile variable message speed signs the district council shifts between 17 sites.
"They can improve road safety by providing real-time information and promoting speed awareness," McCann said.
Both were now showing the correct speed.
