My van keeps jumping out of gear what is the problem

will assume a used van
any warranty ? go back to place of purchase

if a manual ..worn syncros or adjustment to shifter cables

if an automatic a shift soleniod or worn drive clutches

a Fiat Grand cherokee? i know fiat bought jeep but?
is this a motor swap?
jumping, is this a stick shift. do tell?
do tell real car make , year, model and number of gears in trans.
(and if A/T or M/T)

It could be the vacuum modulator on your auto transmission, sometimes when vacuum hoses fail,split or whatever, they can suck up impurities causing other downstream items to fail. Also check mechanical linkage form shifter in cabin to transmission gear selector arm. If jumps were happening these might have worked loose. Best of luck!

Speed sensors will make the van act like that I would take it to a repair shop if they tell u some ridiculous part or price I would shop around there is alot of grimy repair shops out there keep in mind just because they have a national known name dont mean they aint honest

I am experiancing the same thing with my 02 T&C. When the van is shifting out of OverDrive, it is briefly in nuetral causing the van to seem to jump forward, then it shifts hard into a lower gear. I have found that keeping the van in "3" instead of "D" prevents the hard downshift. I am still trying to determine how to permanetaly fix the problem, but until then I keep it in third unless I hit the highway.

Sound like your catilitic converter is plugged and needs replaced,mas air flow senser also ,but I think its your converter

This is all to common a post for your van, read it over and over again, there are class action law suits over this transmission having so many failures, if any money has been paid out i can't say, buy u will need to have the trans removed and torn down and overhauled to correct this problem

if it is standerd then it is most likely your lutch try to keep your r.p.ms at the owest point you can before shifting if it is automatic it could be the pressure plate but im not an expert with automatics{yet again the change them so often that nobody really is}

you might have the module checked but it sounds like the tranny is going out on the van

The gear shift selector is probably "locked you out" because of the fact that there is a Park-Safety solonoid that keeps the car in park unless your foot is depressing the brake so that the gear-shifter cannot come out of park unless a person is trying to move it.

Why that isn't working is probably because the battery on your vehicle is completely 100% dead. If a battery is completely 100% dead, a jump-start is usually not enough to get a vehicle to start because the battery's electrolyte level is so low that it can't actually hold a charge. I recommend you replace the battery at your first convenience, as it will probably alleviate both problems.