![]() ![]() Keep in mind that, in addition to causing foaming, non-compatible fluids may adversely affect steering rack seals, hoses and other soft components in the system. In today’s “quick lube” market, it isn’t unheard of to see power steering reservoirs topped off with brake fluid, engine oil and other non-compatible fluids. In addition, always make sure that an improper fluid hasn’t been introduced into the power steering reservoir. In more rare cases, the hose itself may have a strip of material peeled away from its interior diameter that intermittently clogs the hose and causes pump cavitation or the loss of pressure to the steering rack. ![]() A similar situation can develop if a steering pump return hose is pinched or clogged. In this instance, the pump will emit a growling noise caused by the pump trying to draw fluid through the clogged filter. If the filter is partially clogged, the pump will no longer receive an adequate volume of return fluid from the steering gear or rack. Some imports incorporate a filter or filter screen in the steering pump reservoir. Foaming may also be caused by the power steering pump drawing air past a worn shaft seal during cold operation, or the steering rack drawing air through a leaking seal as the steering rack changes direction. Some Honda models, for instance, 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. Most commonly, the fault lies with a seized support bearing in one of the front MacPherson strut assemblies.ĭiagnostic Summary When diagnosing an assist or noise problem with a power steering pump, always begin by inspecting the condition of the power steering fluid. 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 occasions, 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 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. Power Steering Symptoms 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 require a scan tool capable of accessing the power steering data stream and retrieving diagnostic trouble codes. As axle shaft speed increased, the modulator increased steering sensitivity by reducing power steering fluid pressure to the steering rack.Īlthough a number of steering pump modulation systems have been produced over the years, 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 power steering system, it’s important to access service data describing the operation of the system and how the system should be diagnosed. Power Steering Designs 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. ![]()
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