Foaming power steering fluid image10/3/2023 Some Honda models are known for O-ring failures that cause the steering pump to draw atmospheric air into the pump reservoir. With the engine running, inspect the fluid in the reservoir for signs of aeration or foaming. If the fluid is dark black, the system might have a problem with deteriorating seals in the steering rack or with power steering hoses that are deteriorating from the inside out. When diagnosing an assist or noise problem with a power steering pump, always begin by inspecting the condition of the power steering fluid (See Photo 1). Most commonly, the fault lies with a seized support bearing in one of the front MacPherson strut assemblies. In these cases, the steering gear or rack might have a failed compression disk or similar steering sensitivity device in the metering valve assembly. On rare occasion, power steering assist will be stronger in one direction than the other. In contrast, worn metering valves in steering racks tend to provide sluggish assist when cold and return to normal assist as the assembly warms up and returns to operational tolerances. In most of these cases, the surface of the cam ring develops a rippled surface that allows fluid pressure to leak past the vanes or rollers. In general, worn pumps usually provide good assist when cold, but tend to provide less assist as the power steering fluid warms up. ![]() In this case, the loss of steering assist will be instantaneous and a loss of fluid recirculation will be apparent at the power steering reservoir with the engine running. The only exception to this would be the relatively rare instance when the pump input shaft breaks at the impellor assembly. Most power steering pumps provide ample warning of impending failure. The EVO system, for example, uses vehicle speed, steering wheel position and other inputs to determine the amount of modulation necessary to produce the required steering wheel sensitivity.Īs with any application-specific pressure modulation system, diagnostics requires a scan tool capable of accessing the power steering data stream and retrieving DTCs. Although a number of steering pump modulation systems have been produced over the years, suffice it to say that auto manufacturers have now developed computer-controlled, electronic variable orifice (EVO) power steering pumps that help adapt steering pump pressure to driving conditions.īefore attempting to diagnose any late-model import power steering system, it’s important to access service data describing the operation of the system and how the system should be diagnosed. As axle shaft speed increased, the modulator increased steering sensitivity by reducing power steering fluid pressure to the steering rack. The problem engineers struggle with on power steering is the tendency of the hydraulic boost to insulate the driver from sensing the road surface through the steering wheel on ice-covered roadways or while driving in high-speed road course events.ĭuring the 1980s, Honda addressed this problem by introducing a relatively simple power steering pump pressure modulation system mounted on the transaxle output shaft assembly. ![]() ![]() Malfunctions in either of these systems may require servicing the power steering pump. ![]() In addition to providing hydraulic boost to the power steering system, steering pumps may also power the engine cooling fans on some imports while, in heavy-duty truck applications, may also provide hydraulic boost for the power brakes. Always remember that the amount of power assist delivered to the front wheels depends upon the amount of deflection in the steering gear torsion bar and the amount of port exposure in the metering valve. The pressurized fluid then flows from the steering gear’s metering valve to bear against an assist piston built into the steering gear or steering rack assembly. The more torque applied to the torsion bar, the larger the port area in the metering valve being exposed to pressurized fluid flowing from the power steering pump. When the driver applies force to the steering wheel, he’s actually applying torque to a small torsion bar located in the power steering gear’s metering valve. The pump assembly also contains a flow control valve that responds to pressure and volume demands from the steering gear. The impellor rotates in an off-centered cam ring that causes the impellor to draw in and pressurize the fluid. Power steering pumps are relatively simple devices, with a belt-driven pulley turning a shaft that drives a rotary vane or gear-and-roller impellor.
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