There are three channels, ch0, ch1, and ch2. The second channel, ch1, is capable of outputting up to +20v and the third channel, ch2, is capable of outputting down to -20v. So you can use the last two channels, channel 1 and 2, for +/-4v. When you program ch 2, you must put in -4 as the value. You cannot put in a positive value. However, when wiring, the Lo (-) terminal of ch1 must be wired to the Hi (+) terminal of ch2, and this is your ground reference. The Hi terminal of ch1 will be +4v and the Lo terminal of ch2 will be -4v.
