This article proposes a new adaptive control algorithm for active suspension systems of passenger cars. It combines a proportional–integral–derivative controller for suspension deflection together with a sliding mode reference conditioning outer loop that uses the vertical acceleration of the car body as a complementary source of control. The proposed approach is software-based and allows setting up limit values to critical variables, such as the vertical acceleration, which can be directly tuned by the system designer to range from the original proportional–integral–derivative response to other ones with tighter control on the constrained variable. A longitudinal half-car system subject to irregular excitation from a road surface is used for assessment. The proposed proportional–integral–derivative with sliding mode reference conditioning is compared to the same proportional–integral–derivative controller without the outer conditioning loop, as well as with a passive suspension system. International standards on overall vibration magnitudes are used to quantify the differences obtained in this assessment. Results obtained from the proposed control system show better performance and handle trade-offs, improving the ride comfort without adversely affecting the road holding of the car.