VISTA, Calif. -- A man whose female passenger was killed when his pickup truck crashed after drifting off state Route 78 pleaded guilty Thursday to a felony charge of gross vehicular manslaughter without intoxication.

Charles Eugene Lemay, 28, faces a maximum of six years in prison when he is sentenced Oct. 15 by Vista Judge K. Michael Kirkman.

The defendant's truck went off the side of the freeway near El Camino Real on June 6, 2009, causing the vehicle to roll several times. Vista resident Shannon Maureen Mahoney, 27, was pronounced dead at the scene.

CHP officers had to use a Taser to subdue Lemay after the crash, authorities said.

A breathalyzer test showed a small amount of alcohol in Lemay's system at the time of the crash, according to Deputy District Attorney Lisa Stark.

Lemay was out on bail in connection with the fatal crash when he was re-arrested last May for the alleged sale and transportation of marijuana, the prosecutor said.

Those counts, plus a charge of resisting arrest, were dismissed in exchange for the defendant's guilty plea to the manslaughter charge, Stark said.