Actually, if you'll recall, it turns out that HAL was only lying about the AE35 unit fault...remember? Bowman does an EVA to pull it, he and Poole throw it onto the bench, test it, find nothing wrong, and decide to do another EVA to reinstall it and let it run until it fails, and then...well, you know. HAL just wanted to get them both outside so that he could wreak havoc unmolested.

Talk about "FAIL and You"...