techlink 200012 en - norcal-cobras.com

1 Magnasteer power steering is nowavailable on a wide range of cars from allfive GM is an electronic deviceadded to conventional power rack andpinion steering to vary the amount ofe ff o rt re q u i red to steer the car, depen-dent on vehicle speed. At low speeds,steering eff o rt is lower, for ease in park-ing. As speed increases, steering eff o rtis increased, for greater road d d i t i o n a l l y, on some models, evasivesteering maneuvers also affect steeringe ff o rt .Conventional Rack andPinion Power SteeringOperationAn understanding of Magnasteerbegins with an explanation of conven-tional power steering. In a conventionalpower rack and pinion steering gear, thesteering input shaft is joined to the pin-ion by a torsion bar inside the valveb o d y. Whenever the steering wheel ist u rned, the torsion bar twists slightly (ad e g ree or two) as the steering eff o rt isapplied through the pinion to the re s i s-tance off e red by the front wheels.

2 Thetwo halves of the spool-type hydraulicc o n t rol valve are attached, one at eachend of the torsion bar. So, when the tor-sion bar is twisted, the spool halves arerealigned relative to each other and fluidis permitted to flow through to the steer-ing gear. Steering eff o rt, determined bythe stiffness of the torsion bar and pumpf l o w, is constant at all OperationIn a car equipped with Magnasteer,the basic power rack and pinion steeringsystem continues to function norm a l l does not affect flow, so nor-mal boost is available at all basic Magnasteer system variesonly the driver s steering eff o rt, re g u l a t-ed according to vehicle speed. In curre n tp roduction, Magnasteer is controlled bythe Electronic Brake Control Module(EBCM); a few models in past yearsused a stand-alone module. The EBCM controls current flowt h rough the Magnasteer electro m a g n e t i ccoil, both the amount (amperage) andthe direction (polarity).

3 Pulse width mod-ulation is used to vary the voltage andthe resulting current flow. Current variesbetween -2 and +3 u rre n tflows fro mthe contro l l e rto theM a g n a s t e e rro t a ry actua-t o r, mountedin the steer-ing racka s s e m b l y. Itconsists oftwo magnets,a perm a n e n tmagnet andan electro-m a g n e t .The elec-t ro m a g n e treceives the variable current. The perm a-nent magnet has 30 poles spaced at 12 i n t e rv a l s .T h e re are two separate sets of pole1 Magnasteer Power Steering ..1 Power Steering Analyzer ..3 Identifying OE Engine Oil Filters ..3 Water Inside Rear Spoiler ..3 RKE Receiver Module Location ..3 Engine Performance Diagnosis ..4 Thermistors ..4 Cruise Control Cancels Intermittently ..5 Xtreme Pickup Decal Installation ..5GM Service Clubs, Part 2 ..6 Service Operations Advisory Group ..6 TAC Tips ..7 Tacker Sensitivity to Vibrations.

4 7 Service Bulletin Based on Reader Information ..7 Bulletins ..8 Thanks for Information ..8 Tire Pressure Monitor Tool ..8 ContentsService OperationsDecember 2000 Volume 2, No. 12continued on page 22continued from page 1GM techlink is a monthly magazine forall GM retail technicians and serviceconsultants providing timely informationto help increase knowledge about GMproducts and improve the performanceof the service department. This maga-zine is a companion to the GM Communications Gracemary AllenPublisher & Editor:Mark StesneyGM Service Operations Editor:Jim Horner Manager:Marie MeredithDesktop Publishing:Greg Szpaichler, MediaWurks number: 1-248-649-5465 Write to: TechLinkPO Box 500 Troy, MI 48007-0500 General Motors service tips ar eintended for use by professional tech-nicians, not a "do-it-yourselfer." Theyare written to inform those techni-cians of conditions that may occur onsome vehicles, or to provide informa-tion that could assist in the properservice of a vehicle.

5 Properly trainedtechnicians have the equipment, tools,safety instructions and know-how todo a job properly and safely. If a con-dition is described, do not assumethat the bulletin applies to your vehi-cle or that your vehicle will have thatcondition. See a General Motors deal-er servicing your brand of GeneralMotors vehicle for information onwhether your vehicle may benefit fromthe in this publication is not nec-essarily an endorsement of the indi-vidual or the 2000 General Motors CorporationAll rights , inner and outer, which close themagnetic field. The permanent magnetsits between the inner and outer poles ofthe electro m a g n e t .The strength and polarity of the mag-netic field in the electromagnet deter-mines the effect Magnasteer has onsteering zero mph, negative current flowst h o rough the electromagnet, and themagnets begin to repel each other.

6 Them o re the magnets repel each other,s t e e r i n ge ff o rtd e c re a s e s ,as thoughthe torsionbar becamel i g h t e r. Thisis thed e s i re dcondition atlow ro a ds p e e d s ,such asp a r k i n g .A tabout 45mph, thereis no cur-rent flowt h rough them a g n e t i ccoil, so steering eff o rt is determined onlyby the torsion bar and pump 45 mph, current flows in apositive direction and increases as speedi n c reases. The electromagnetic polepieces and the permanent magnet attracteach other, which raises the torsionalrate of the steering gear, and adds tosteering eff o rt. It s as though the torsionbar gradually became stiff e r. This pro-vides greater road added feature on someMagnasteer systems comes into play ina skidding condition. If excessive lateralG - f o rces are detected, Magnasteeri n c reases steering eff o rt, to encouragethe driver not to MAGeThe latest version of Magnasteer elim-inates the permanent magnet.

7 In thisf o rm, one pole piece of the electro m a g-net is mounted to the input shaft and theother to the pinion shaft. At the lowestspeeds, there is no current flow thro u g hthe electromagnet, and steering eff o rt isdependent only on the stiffness of thetorsion bar. As speed increases, curre n tflow through the electromagnet incre a s-es, and steering eff o rt incre a s e s .In this version, the Magnasteer eff e c tdepends entirely on road speed, andt h e re is no change during evasive maneu-vers. Only a highly informed driver could tellthe diff e rence between e g a rdless of which version ofMagnasteer is installed on a vehicle, thee ffect on the driver is the same -- steeringe ff o rt is noticeably easier at low speedsand increases as the car goes may be re q u i red, based onone of three driver concern s .1. Light steering eff o rt at all speeds2.

8 Heavy steering eff o rt at all speeds3. Erratic steering eff o rt levels at vari-ous speedsSystematic diagnostic pro c e d u res arep resented in the appropriate serv i c em a n u a l .N O T E :The Magnasteer system onsome vehicle lines can be recalibrated forsteering eff o rt, using the Tech 2. Therea re three settings: Factory, More Firm ,and Less Firm. On those vehicles whererecalibration is available, use this featureonly at the customer s request. Refer tothe appropriate service manual fordetails. The Magnasteer activator is serv i c e-able only by replacing the entire steeringrack assembly. Individual components arenot TestingMalfunctions in the electronic por-tions of the Magnasteer system are diag-nosed using the Tech 2 to access diag-nostic Testing TipsThe power steering system section ofthe service manual presents a test pro c e-d u re for the Magnasteer hydraulic com-ponents, which are the same as thoseused in non-Magnasteer systems.

9 Use oftester J-44721 permits you to test theoperation of the steering gear and thepump, and identify system re s t r i c t i o n s . Ken Hill and Scott Bower contributed tothis SteeringAnalyzerPower Steering Analyzer J-44721, anew essential tool, has been released byK e n t - M o o re and will be in yourdealership soon. You ll need it top e rf o rm the power steering sys-tem diagnostic pro c e d u res in the2001 service J-44721 analyzer is anupdated version of the J-25323a n a l y z e r, which was pre v i o u s l yessential for Oldsmobile dealersand available to all you already have theJ-25323, you can convert it tobecome the J-44721 by adding thecomponents in kit major diff e rence betweenthe two analyzers is that the J-44721 is equipped with two pre s s u regauges instead of one, for accurate re a d-ings at both low and high pre s s u re s.

10 Also, the J-44721 includes an adaptera s s o rtment that permits using the ana-lyzer on all current GM cars and tru c k s .In addition tothe pre s s u regauges, the analyz-er contains a flow meter to measurefluid flow under various conditions. And,a valve permits adding a variable re s t r i c-tion to the circuit as called for in the ser-vice manual pro c e d u re s .Testing TipsThe power steering system sectionof the service manual provides a testp ro c e d u re for the power steering systemhydraulic components. Use of analyzer J-44721 permits you to test the opera-tion of the steering gear and the pump,and identify system restrictions that maybe present in the pre s s u re or re t u rnl i n e s .The analyzer is installed in the pre s-s u re line between the pump and thesteering gear. If the system has beenre p a i red, accurate diagnosisre q u i res that the system be bledof air before beginning the , any air introduced dur-ing the installation of the analyz-er must be purged.