The following is the Code 2018 Draft 2 version.
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2.6 Accept only those responsibilities for which you have or can obtain the necessary expertise, and honor those commitments.
A computing professional has a responsibility to evaluate every potential work assignment. If the professional's evaluation reveals that the project is infeasible, or should not be attempted for other reasons, then the professional should disclose this to the employer or client, and decline to attempt the assignment in its current form.
Once it is decided that a project is feasible and advisable, the professional should make a judgment about whether the project is appropriate to the professional's expertise. If the professional does not currently have the expertise necessary to complete the project the professional should disclose this shortcoming to the employer or client. The client or employer may decide to pursue the project with the professional after time for additional training, to pursue the project with someone else who has the required expertise, or to forego the project.
The major underlying principle here is the obligation to accept personal accountability for professional work. The computing professional's ethical judgment should be the final guide in deciding whether to proceed.