KENNEBUNK (AP) — Maine Turnpike officials say some drivers who use electronic E-ZPass transponders may have been overcharged.

The problem was caused by a damaged road sensor on a ramp at the Kennebunk toll plaza that counts the number of axles per vehicle. A Turnpike Authority spokeswoman says the sensor may have counted extra axles on some vehicles, resulting in higher tolls.

The problem may have been happening for three months but was only discovered last week when an E-ZPass customer complained about being overcharged.

Turnpike spokeswoman Erin Courtney said the overcharge did not occur on every trip through the plaza. She says one woman was charged extra 36 times out of 501 trips.

E-ZPass customers who use the Kennebunk plaza are being urged to check their statements.