Got a new XBox for my son and got him the Forza 6 . He can play in the test drive and the car accelerates but it in the career mode he cant accelerate any of the cars he has. Got him a 10 year anniversary pack, but it still does not let him accelerate in free play too. I am a newbie and do not have clue on what is wrong or what needs to be done. Can anyone please advise.
Thank you for your help.
Has he possibly got manual gear with clutch selected?
Go to assist and make sure it’s in manual!
Hope this is it 
Thank you for the reply. It was in some Dare mode , not sure what is a dare mode. Once we removed dare mode went to automatic using assists . Thank you so much ,things look much better now
Mods modify racing conditions by giving your car enhancements such as extra power or improved handling, or by giving you a challenge such as disabling a feature such as automatic transmission.
You don’t have to use mods if you don’t want to, or you can use them to make bonus CR or XP. You set or reset mods from the game menu just before you start a race.
It sounds like a ‘Mod’ card rather than a mode. Glad you got sorted out though.
Mod cards allow you to apply certain characteristics to your car - whether they be Dare (making the game harder - dependant on skill level - such as utilising manual or disabling other assists, starting further back in the pack that sort of thing - for an increased credit reward at the end). Others mod’s can make your life easier, increased grip, lower weight, higher power - that sort of thing. You can also get cards that might reward you for passing other cars or other challenges.
You don’t have to use them and some are one use only - just check before you start a race if you have one equipped or not. I tend not to use them although have used a couple in career to spice things up from time to time.
Check out the thread entitled Mods in FM6 for more information
Thank you. Yes it is Mod (you can see my knowledge of the game 
but learning with my son) it is really a lot of learning on how to use them to start in the race. If we use them is do we need to change the cars’ defaults / configuration using the assists or something else is needed. But glad that it is working now during the holidays
They will generally tell you what they will do, whether it be turn off traction control or another assist (with the dare cards) or increase grip with a crew card or boost XP with a boost card.
If you have a certain assist set up, say automatic transmission, the use of a Mod card which requires you to use manual will override the assist you have set up. So you don’t have to change a setting as such - disable the Mod card, you regain the use of Automatic but having that particular Mod card equipped will mean you have to use what it says on the Mod card.
I’d stay away from using dare cards until you’re comfortable with the game and or have started experimenting with driving without those assists anyway.
Welcome to Forza, hopefully you & your son have lots of fun with the game & don’t worry about asking any questions, there are a lot of people willing to answer anything you may not be sure about.
Just curious, what was the dare mod?
If he was in an F1 car then probably Manual with Clutch. If it was any other car than it could have been Severe Power Decrease.