Currently, most automotive and truck power steering systems involve an engine-driven pump, pushing hydraulic fluid at high pressure through hoses to the steering gear, producing the necessary power assist. Common usage of this arrangement goes back more than 50 years. Today, additional electronic components are often added to vary the amount of assist, protect against overheating, and other situations.

However, the hydraulic pump system is facing quick extinction in the face of rapidly advancing electric power steering system technologies.

Electric power steering systems replace the entire hydraulic assist system with a powerful electric motor, built into the steering assembly and driving it directly.

The disadvantages of the old hydraulic systems are almost too numerous to mention, although no all-around better technology emerged until recently. The hydraulic pumps are a major source of parasitic power losses, often prohibiting their use on small engines. That same parasitic power drain also drives down fuel economy. Hydraulic systems are a complicated mix of maintenance-intensive components, they are prone to leaks, use heavy and expensive components, and require large amounts of underhood space which is increasingly at a premium. Environmental issues stem from the use of hydraulic fluid and are becoming increasingly troublesome, especially in the vehicle's recyclability. And the pump must always be running when the engine is running for there to be power assist, even when there is no steering input. The units are also a source of block-mounted engine noise.

In contrast, electric power steering systems can be exceptionally compact, packaged with the steering gear. The units are relatively light and far simpler to design, build and maintain. Sensors, often mounted on the steering column, measure the angular position of the steering wheel, feeding the information into a computer and telling the system how much power assist to use and when. Tied to a vehicle's electronic stability system, the steering can be programmed to provide widely varying levels of assistance at any engine speed (more assist when parking, for example). By eliminating parasitic losses, power steering can be made available even on small-engined vehicles. Design and packaging allows a single unit to be used across a wide variety of vehicles, simplifying engineering and lowering costs. The units are also extremely quiet, meeting buyers' increasingly demanding taste for smoother, quieter vehicles. The units only operate when steering input is needed, improving efficiency and extending component life. Finally, the hydraulic fluid environmental and recycling issues are eliminated.

Although electric power steering systems offer significant advantages over their hydraulic counterparts, electric motor technology and controls had not reached the point where they could be used in this application until just recently. In the mid-1980's, for example, TRW had a working electric power steering system but it had an unfortunate tendency to completely drain the battery during a single parking maneuver.

New generations of materials, sophisticated computerized electronic control systems and advancements in power management have all contributed to making electric power steering assist a reality.

The 1990 Acura NSX was the first production vehicle to use a fully electronic steering rack, a unit from Showa. The 2000 Fiat Punto used Delphi's E-STEER electric power steering system in the first high-volume production application. Volkswagen's 2001 Lupo 3L TDI can be optioned with E-STEER for 1.3 MPG better fuel economy. Honda's Insight, Prelude and S2000 use Showa electric power steering and the new MGF uses EPAS. The Saturn Vue will use a unit from Koyo.

Other issues are also driving the move toward electric assist. In electric and hybrid vehicles such as the Honda Insight, the engine does not run continuously so electric power steering is the only possible route. Programmable steering response also allows additional return-to-center action, freeing chassis engineers to pursue more aggressive wheel alignment specifications and suspension geometries. Similarly, the units can be programmed to eliminate steering wheel kickback over rough surfaces. Finally, maintenance is eliminated for the life of the vehicle and the unit is readily recycled.

Fuel economy improvements with electric power steering vary by vehicle and engine size, but normally vary from 1 to 3 miles per gallon. That is a very large savings obtainable by OEMs without requiring extensive drivetrain or combustion engineering.

Electric power steering has now become such a compelling technology that 30% of the world's vehicle production (approximately 20 million units) will use it by the 2003 model year. Many industry experts expect hydraulic power steering will disappear from new cars within 5 to 7 model years.

Manufacturers of electronic power steering systems include Koyo, NSK, Delphi, Showa, Visteon, and ZF Freidrichshafen AG.