I had one in my Journey and if it's the kind of sofa that has the handle above the lower section that you lift up to pull out the foot rest, I had a devil of a time when the little 'S' end of the remote release cable broke off. Couldn't find anything close to a replacement.
Hard to remember but I think I was able to pull out the foot rest (spanned the entire sofa) just a couple inches and slip my hand down there to the mechanism attached to the floor, under the middle of the couch, and with my fingers, lift up on the pin. Or I may have used my extra long needle nosed pliers to grab it.
I've since sold that sofa during a remodel so I don't have it to look at. What I did as a work around was to tie a nylon cord to the latch pin release and draped it out of the hole where you usually reach in to pull up the remote release. Heavy steel washer on the exposed end of the cord.
I'll go look for the article I wrote about it on my blog...it seems it has disappeared. Had pics and everything.
Can't find the article that directly addressed opening the trundle section when the cable breaks but here are some pictures of the sofa. You can see the washer in the middle of the sofa coming out of the hand grab in my ad free blog article here:
Furniture
: 
Linear Mode
