Setting up ADS1216 to use IDAC
TI chips are complex usually with two or three registers that need to be set before any operation happens.

Since you haven't added any info on your setup OR your register settings, I'll assume the worst. 

Make sure these things are happening:
1) That your measuring current with a low impedance pathway (like 20k to 150k). I don't think your doing this but just know what the load is on the DAC. 

2) Set the ACR range register to max current (which is 3)  

3) Make sure the REF_EN pin is enabled if you don't have an external reference.

Set the voltage then measure the voltage with no load, if your not seeing a voltage then you are probably not setting registers right. If you do see a voltage then put a higher load like the 150k to ground and measure the voltage, it should be the really close to the no load voltage.