Falsifying qualifications and other paperwork, which is also expressly forbidden in the code, would qualify as legal fraud in most instances, and would be punishable through both criminal and civil actions (NSPE 2007). Other provisions of the code are more purely ethical; the disclosure of conflicts of interest, even seemingly minor ones, would not always be a legal requirement (especially when the engineer is engaged in private projects with non-publicly traded companies/entities). The maintenance of public welfare that is the preeminent and paramount duty of engineers according to the code is also above and beyond the purely legal requirements (NSPE 2007). One of the major purposes for the development and adoption of a code of ethics is to establish consistent practices -- and thus expectations -- within a profession (Davis 1991). This creates a system of ethics and conduct that serves almost all ethical frameworks that could...

The consistent practices lead to (more) consistent results, satisfying the needs of consequential ethical systems. Deontological ethicists can also find reasons to approve of these consistent codes, as they demonstrate -- often explicitly -- the general universal practices and intentions that must be applied in order to achieve desired results.
References,

Davis, M. (1991). "Thinking like an engineer." Princeton university press. Accessed 6 February 2010. http://ethics.iit.edu/publication/md_te.html

NSPE. (2007). Code of ethics for engineers. National society of professional engineers. Accessed 6 February 2010. http://www.nspe.org/resources/pdfs/Ethics/CodeofEthics/Code-2007-July.pdf

TAMU. (2008). "Introducing Ethics Case Studies Into Required Undergraduate Engineering Courses." Texas A&M university. Accessed 6 February 2010. http://ethics.tamu.edu/