Roberto Orci, head writer on Transformers:Revenge Of The Fallen, the sequel to the blockbuster of two summers ago, claimed in a web chat on fan-site TFW2005 that the Chevy Volt was not in the original script, but rather was foisted upon them at the last minute.
When asked the question:
Was the Chevy Volt TF kind of shoved into the film by GM and not really in the script?
Yes. Had to figure it out last minute.
This confirms other reports we'd heard from movie insiders who've told us the Volt was a last minute requested addition by the General. Apparently, the GM team was adamant the Volt be included and wouldn't take no for an answer. Keep in mind this is different than what Michael Bay did in the first movie — personally selecting all the vehicles to appear in the film. (Hat tip to Jack!)