Why would they?

After Daimler-Benz wasn't able to bring these changes about, why would Fiat want to try?
The official said there were encouraging signs that the Chrysler merger with Fiat will happen soon. The administration wants this deal to happen, but has tried to avoid too big a stake by Fiat for fear that taxpayers would be funding a foreign takeover.

Fiat will commit to produce fuel-efficient cars and engines in the United States, and will be limited to a 49 percent stake until all taxpayer loans have been repaid. There are no expected leadership changes at Chrysler, given the ongoing merger talks. [...]

It noted that none of Chrysler's current models were recommended in a recent article by Consumer Reports and that every one of its brands ranked in the lower quartile for quality in an assessment by J.D. Power.

It said the company is too dependent on its truck and SUV business and had only a 3 percent share of the small-car market, even though that segment makes up 21 percent of car sales overall. Noting that Chrysler's strength is in trucks, SUVs and mini-vans, all vehicles with relatively low fuel efficiency, the government said it was unlikely Chrysler would be able to meet new government standards for fuel consumption.
Fiat could just wait until Chrysler is in bankruptcy and then buy up the pieces they want and leave the rest behind.