This guidance document establishes the Maximum Allowable Emissions Limit (MAEL) as an objective screening tool to assist nonroad Compression Ignition (CI) engine manufacturers and EPA in evaluating off-cycle emissions from base emission control strategies as they relate to the prohibition of defeat devices. As described in previous EPA guidance, base emissions control calibrations meet the definition of an auxiliary emissions control device (AECD). See EPA Guidance Document VPCD 98-13 (VPCD-98-13) and Advisory Circular 24-3 (A/C 24-3). This guidance explains how EPA will use MAEL data voluntarily submitted by manufacturers to evaluate base emissions control calibrations not substantially included in the Federal Test Procedure (FTP) for compliance with the defeat device provisions in 40 CFR Part 89 Section 107. The MAEL is intended to assure engines are calibrated to provide emissions control similar to that demonstrated over the 8-mode certification test cycle across the operating range, and not just at the 8 predefined test points.