(a) Selective enforcement audits apply for engines as specified in 40 CFR part 1068, subpart E. This section describes how this applies uniquely in certain circumstances.

(b) Selective enforcement audit provisions apply with respect to your fuel maps as follows:

(1) A selective enforcement audit for an engine with respect to fuel maps would consist of performing measurements with production engines to determine fuel-consumption rates as declared for GEM simulations, and running GEM for the vehicle configurations specified in paragraph (b)(2) of this section based on those measured values. The engine is considered passing for a given configuration if the new modeled emission result for each applicable duty cycle is at or below the modeled emission result corresponding to the declared GEM inputs. The engine is considered failing for a given configuration if the new modeled emission result for any applicable duty cycle is above the modeled emission result corresponding to the declared GEM inputs.

(2) Evaluate cycle-average fuel maps by running GEM based on simulated vehicle configurations representing the interpolated center of every group of four test points that define a boundary of cycle work and average engine speed divided by average vehicle speed. These simulated vehicle configurations are defined from the four surrounding points based on averaging values for vehicle mass, drag area (if applicable), tire rolling resistance, tire size, and axle ratio. The regulatory subcategory is defined by the regulatory subcategory of the vehicle configuration with the greatest mass from those four test points. Figure 1 of this section illustrates a determination of vehicle configurations for engines used in tractors and Vocational HDV using a fixed tire size (see §1036.540(c)(3)(iii)). The vehicle configuration from the upper-left quadrant is defined by values for Tests 1, 2, 4, and 5 from Table 3 of §1036.540. Calculate vehicle mass as the average of the values from the four tests. Determine the weight reduction needed for GEM to simulate this calculated vehicle mass by comparing the average vehicle mass to the default vehicle mass for the vehicle subcategory from the four points that has the greatest mass, with the understanding that two-thirds of weight reduction for tractors is applied to vehicle weight and one-third is understood to represent increased payload. This is expressed mathematically as Mavg = Msubcategory − 2⁄3 · Mreduction, which can be solved for Mreduction. For vocational vehicles, half of weight reduction is applied to vehicle weight and half is understood to represent increased payload. Use the following values for default vehicle masses by vehicle subcategory:

(3) This paragraph (b)(3) provides an example to illustrate how to determine GEM input values for the four vehicle configurations identified in paragraph (b)(2) of this section. If axle ratio is 2.5 for Tests 1 and 2, and 3.5 for Tests 4 and 5, the average value is 3.0. A tire size of 500 revolutions per mile would apply for all four tests, so the average tire size would be that same value. Similarly, Crr is 6.9 kg/tonne since that value applies for all four points. The calculated average value of CdA is 6.9 m2. The calculated average vehicle mass is 28,746.5 kg. Weight reduction is 4,847 kg or 10,686 pounds ( 3⁄2 · (31,978 − 28,746.5)).

(4) Because your cycle-average map may have more or fewer test points, you may have more than or fewer than the number of audit points shown in Figure 1 of this section. If the audit includes fuel-map testing in conjunction with engine testing relative to exhaust emission standards, the fuel-map simulations for the whole set of vehicles and duty cycles counts as a single test result for purposes of evaluating whether the engine family meets the pass-fail criteria under 40 CFR 1068.420. If the audit includes only fuel-map testing, determine emission results from at least three different engine configurations simulated with each applicable vehicle configuration identified in §1036.540; the fuel-map simulation for each vehicle configuration counts as a separate test for the engine.

(c) If your certification includes powertrain testing as specified in 40 CFR 1036.630, these selective enforcement audit provisions apply with respect to powertrain test results as specified in 40 CFR part 1037, subpart D, and 40 CFR 1037.550. We may allow manufacturers to instead perform the engine-based testing to simulate the powertrain test as specified in 40 CFR 1037.551.

(d) We may suspend or revoke certificates for any appropriate configurations within one or more engine families based on the outcome of a selective enforcement audit.