Diehl made the plea Monday to aggravated DWI and impaired driving in Queens Criminal Court, according to the New York Daily News. Diehl was sentenced to six months probation, and ordered to pay $1,200 in restitution and $300 in fines. He must also wear an alcohol-monitoring "scram" bracelet for 90 days.
At the time of his June 2012 arrest, Diehl failed a breathalyzer test which revealed a blood-alcohol-content level of .18, more than twice the legal limit, according to WNBC-TV.
Diehl's play slipped in his 11th NFL season, and he's a prime candidate to be released by the Giants in the near future. He has one year and $4.475 million remaining on a six-year contract he signed in 2008.
Follow Dan Hanzus on Twitter @DanHanzus.