ELECTRO-HYDRAULIC POWER STEERING FAILURE

ELECTRO-HYDRAULIC POWER STEERING FAILURE 

In a matter of just a few short days, I've received a flurry of assistance requests from several VW owners,  all of whom seem to have power steering issues of some sort or the other. These issues ranging from complete failure of power steering to intermittent steering assist, to stiff and hard to steer. Among  the vehicles affected are VW Jettas,  Volkswagen transporters, Volkswagen Passats,  VW MKIV  TDI's and Golf Mk5s. Unfortunately specifics about steering problem can vary tremendously because some VAG vehicles are Hydraulically controlled, whereas some are electronic and others are ally controlled, all of which use slightly different technologies and components often spacely dissimilar.   

This implies some vehicles will have a Power steering pump as part of the steering rack assembly whereas others will have a power steering motor / hydraulic fluid reservoir a good meter separated from the steering rack. The following is  a general overview of the operation of VAG power steering systems. But what all these systems have in common, is the dreaded yellow steering light on the instrument panel which lights up for a 3- 4 seconds when the ignition is switched on but goes out after the engine is started. This is part of the self test that checks all electronic modules and mechanical mechanisms are synchronised to work together in harmony. However when the Servotronic warning lamp K92 stays on after the engine is started, there is definitely a fault with the power steering system.


When this happens it is a good idea to book the car in for repairs or do the repairs yourself because it could be quite  expensive.  Either way get the vehicle off the public road because loss of steering while driving can be very dangerous if not fatal especially going around corners because of the possibility of over steer.  An electro-hydraulic power steering system is fairly intricate because its control modules are interconnected. The Power steering control module controls the hydraulic pump motor which produces the hydraulic pressure needed for the steering servo assistance. But in order to this, it needs signals from the 'Powers steering sensor' which is located in the steering column and from the speedometer sensor via the 'Instrument cluster control Module' which is responsible for turning on the yellow steering wheel symbol should there be a problem. And lastly the Power steering controller also needs the engine speed data from the 'Motronic control Unit'. It also needs a 12V supply from terminal 30 as well as 12 volts supply from terminal 15 and of course an earth connection. The power wires are fairly thick and chunky which implies high current delivery. Poor electrical connection can cause arching which will disrupt functionality. Loss of any of signals or voltages to the Power Steering control module for even a few seconds will interrupt steering assist and make the car hard to steer. 

In a previous blog I described the  steering loss I encountered due to loss of  voltage to my car's hydraulic pump motor because my positive battery terminal was loose which resulted in intermittent supply to the main steering control module. It is worthwhile to  to check the level of the Hydraulic fluid in the reservoir when you suffer hard of stiff steering. If there is a leak, the hydraulic pump motor cannot produce the necessary pressure resulting in stiff steering. If the fluid is low, refill the reservoir but don't start the engine but get someone to continually turn the steering wheel between the left and right extremes while waiting for all air bubbles to surface. When the appearance of air bubbles  ceases, it would be ok to start the engine. It is also worth your while to   check for DTC's with a scan tool. Should there be a steering error,  deleting often restores steering assist. The LenkhilfeTRW V270 used in the Polo 9N is normally coded as 10110 which can be changed to 10120, 10130 or 10140 in order to incrementally increase the stiffness of the steering. For more Steering codings click here.