A control method for an engine of a vehicle includes generating a brake value indicative of an operating condition of a brake system of the vehicle, and selectively adjusting one of a fuel control value of the engine and a fuel adjustment diagnostic value for the engine based on the brake value. In the method, a mass of fuel delivered to the engine is based on the fuel control value, and a diagnostic result indicative of lean operation of the engine is based on the fuel adjustment diagnostic value. The brake operating condition is selected from a group including a state of operation, a pedal displacement, an actuation period, a fluid operating pressure, and a power assist pressure. The fuel control value is provided.