The `Dear John` star was driving to an interview in Los Angeles, but stopped when he saw a woman trying to push her car down a dangerous exit ramp.
He stopped, telling the woman: "The car`s smoking. Maybe it`s on fire."
Noticing that the lady had a child in the back of her car, who turned out to be her grandson, he got him out of the vehicle, before trying to find out what was wrong with the car and calling a tow truck company.
The actor`s chauffer was able to make some rudimentary repairs to the car, which would be enough for the driver to make it to the next service station, and Channing gave the lady $100 to help cover the cost of the repair.
He told Details magazine he then told her: "Get it fixed. Go fix it now. Don`t get stuck out here again. Take it slow. Put on your flashers."
Meanwhile, Channing has also admitted he has taken some of the romantic lead roles in past films, such as `She`s the Man` and `Step Up` in order to learn, as he has had little formal acting training.
He explained: "You gotta do the `Dear John`s.` You gotta do `The Vow`. I`m conscious about why I did those parts, those movies. I didn`t go to acting school, so my knowledge of story, filmmaking, and character comes from just being on set and doing it. I know I`m not the best actor, but I hope my characters are getting better."