According to http://www.gradeinflation.com/tcr2010grading.pdf (figure 3 on page 4), natural sciences (of which biology is the largest category) tended to have slightly lower grades than engineering as of around 2006.
However, engineering major requirements tend to be more voluminous than the natural sciences major requirements, so there may be less ability to cherry-pick elective GPA-boosting courses for engineering majors than natural science majors.