Electronically Controlled Viscous Cooling Fan

1 1 July 2002 Volume 4, No. 7A monthly publication for GM Dealership Service ProfessionalsContentsElectronically Controlled Viscous Cooling Fan ..1PI Documents Coming to SI ..1 Class 2 Corner ..2 Tech TipsSteering Column Rattle ..2 Bed Rail Installation ..2 Restricted EVAP Vent Path ..4 Tracker Window Glass Binds, Tips ..4 Updates for NVG 246 Transfer Case ..4 Quadrasteer Learn Wheel Alignment ..5 Seat Adjuster Repairs ..5 Door Water Deflector ..6 Sunshade Wires Pinched ..6 TAC TipsAllison Transmission Shift Busyness ..6 Perceived Overspeed During Decel ..7 Allison LCT000 Transmission ..7 Radio Assistance for Cadillac CTS ..7 Door Trim Panel Hooks Broken ..7 Bulletins ..8 techline Newsbe minimal to start, and will increaseover time. The Vehicle Identification Number (VIN)is required to access the PI text. The PIis tied to a specific vehicle and concern. It is important to understand that a PImay apply to one vehicle and notnecessarily another, because of thesymptom/concerns.

2 It is also importantto access SI each time you work on avehicle, to get any PIs that may applydirectly to that vehicle. Due to the SI publication timetable, PIinformation will be available throughTAC 1 10 days before the informationis available in SI. PIs that do not indicate specific fixeswill not be available through SI. Preliminary Information is often thebasis for bulletins and changes in SIService Manuals. When this occurs, thePI will be removed from fan clutches have been used onGM vehicles for many years, because theyimprove fuel economy and emissions, andcontribute to lower engine noise , most rear-drive vehicles havebeen equipped with a thermostatic fanclutch, or in some cases, an electric engine (RPO LL8) in the 2002 Chevrolet TrailBlazer, GMC Envoy, andOldsmobile Bravada uses an all-new PCM- Controlled Electro- Viscous (EV) Cooling fan. In2003, this same device will appear on (LM4) mid-size truck compared with the conventionalfan clutch, the EV fan offers several benefits: Improved A/C idle and city trafficperformance Reduced noise Reduced A/C compressor warranty,because the A/C system operates at alower head pressureElectronically Controlled Viscous Cooling FanPreliminary Information (PI) Documents Coming to SIcontinued on page 2In the past, if you were working on avehicle condition that was not addressed inSI, you could check the list of ProductInformation (PI) documents to see if one ofthe titles sounded like it would be you had to call Technical Assistancefor specific repair suggestions contained inthe were put in place on the SIwebsite the week of June 17 allowing youto find both the title and the text ofProduct Information documents yourself.

3 And, the CD version will be updated toreflect the PI enhancement in July when anew set of SI CDs are shipped to yourdealership. Here are the highlights of this new service: Technical Assistance is reviewingcurrent PI information and if appropriate,will republish the information in the newformat that will be viewable in SI. The amount of PI information in SI maycontinued on page 3 Service and Parts Operations2 techline News continued from page 1patience during this transition is appreciated. Remember, the Service and PartsOperations website can be accessed If you havequestions regarding the content of thismessage, please contact the TechnicalAssistance Center at Thanks to Beth GrotzDirector, GM Technical Assistance Center GM 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. Thismagazine is a companion to the GMEdge & Editor:Mark StesneyGM Service Editor:Jim Manager:Marie MeredithDesktop Publishing:Greg Szpaichler, number: 1-248-649-5465 Write to: TechLinkPO Box 500 Troy, MI 48007-0500GM TechLink on the Web: Motors service tips are intendedfor use by professional technicians, not a"do-it-yourselfer.

4 " They are written toinform those technicians of conditionsthat may occur on some vehicles, or toprovide information that could assist inthe proper service of a vehicle. Properlytrained technicians have the equipment,tools, safety instructions and know-howto do a job properly and safely. If acondition is described, do not assumethat the bulletin applies to your vehicleor that your vehicle will have thatcondition. See a General Motors dealerservicing your brand of General Motorsvehicle for information on whether yourvehicle may benefit from the in this publication is notnecessarily an endorsement of theindividual or the 2002 General Motors CorporationAll rights the goal of this new activity isto put more information in your hands atthe dealership, do not hesitate to call TACif you need further assistance. The team atTAC is always available to help you withyour diagnostic access to PI text is the numberone request that TAC hears fromtechnicians. However, as with any change, itwill take time to build the system to whereit needs to be.

5 Your cooperation andOn vehicles with a Star configuration, asplice pack (Star Connector) houses theClass 2 wires coming from each of thecontrollers. The location of these splice packsvaries from vehicle to :See the June 2002 issue for adescription of Star the location can vary, it may benecessary to use SI to locate the splice the proper vehicle has been selected,type DLC into the search box. This will bringup the Data Link Connector Schematic. Thiswill show the controllers and how the Class2 bus is wired and also if there is a splicepack used. In the upper right corner of the un-zoomed schematic will be a hyperlink labeledLOC, which stands for location. Clicking thiswill bring up the Master ElectricalComponent List. Look down the list for StarConnector and click on the ComponentViews hyperlink for a picture of the locationor Connector End View for a pinout of thesplice :Not all vehicles use splice packs. Forinstance on the GMT400 family of pickupsand utilities, the Class 2 wires were crimpedand soldered in traditional harness buildingstyle.

6 Thanks to Mark HarrisOwners of some 1999-2002 Sierra orSilverado 2500HD and 1500HD pickups maycomment about a rattle noise from thesteering column, particularly during lowspeed parking lot new stub shaft bearing kit 26099860has been released to address this issue. Thekit contains a bearing, a packet of lubricantand :The new bearing is a tight hand :For installation, you must useessential tool J-45798 to avoid damage toSteering Column RattleWhen installing accessory bed rails on a1996-2002 Chevrolet S-10 or GMC Sonomapickup, observe these follow the instructions that comewith the bed rails. The pickup bed may bedamaged if the rails are reversed or thefasteners are RailInstallationthe bearing seal. This tool has been :It is not necessary to replace the I-shaft for this condition. Although thesymptoms are similar, this is not the samecondition mentioned in bulletin 00-02-35-003A. Thanks to Steve LoveBe careful when center punching the bedrail for not use a click-type torque wrench orexceed 60 lb in ( Nm).

7 Thanks to Dan OdenBearing Installer J-457983 Reduced parasitic losses, for improvedfuel economy Reduced false engagements at stop lightidlesReview of ConventionalThermostatic Fan ClutchThe conventional thermostatic clutch is afluid coupling, belt-driven by the engine. Theamount of fluid in the coupling is controlledby a bimetallic coil spring attached to a fluid is admitted into the coupling athigher temperatures, causing the fan rotationto increase. At lower temperatures, thespring closes the valve, decreasing fluid inthe coupling, and the fan rotation is pumped from a reservoir in thefan clutch into the coupling by the action ofthe fan Fan OperationThe EV fan clutch also operates bycontrolling the amount of fluid admitted intothe coupling. But instead of a bimetallicspring, the valve is operated by an solenoid is Controlled by a solid-statedevice, operated by a pulse-width-modulated(PWM) signal from the PCM. As thecommanded state of the fan clutchincreases, so does the ON time of the the relay ON time directly affects theamount of time the solenoid in the fan clutchis :The fan is disengaged at 0% dutycycle and fully engaged at 100% duty fan is commanded to 100% if: engine coolant temperature exceeds264 F (129 C) transmission oil temperature exceedsapproximately 304 F (151 C) A/C refrigerant pressure exceeds 240 psi(1655 kPa) certain DTCs are fan is commanded to less than 100%under all other PCM uses information from thefollowing sensors to determine theappropriate duty cycle: Engine coolant temperature Transmission oil temperature Ambient air temperature A/C reference pressure Vehicle speed EV fan Hall effect sensorThe PCM monitors the performance ofthe Cooling fan using a Hall effect sensor,which reads a reluctor track inside the fanclutch.

8 The PCM supplies a 5-volt referenceand a low reference to the Hall effect sensor returns a signal pulse through thecooling fan speed signal circuit. 1 hz on thecooling fan speed signal circuit equals about1 rpm of actual fan speed. By comparing theactual and desired fan speeds, the PCM isable to determine if the fan is working asdesigned. If not, it will set related DTCs Function Check The EV Cooling fan can be Controlled in10% increments using the Tech 2. TIP:Follow this path on your Tech 2:F0: PowertrainF2: Special FunctionsF0: Engine Output ControlsF0: Electro- Viscous FanTIP:Because fluid has to bleed in and outof the coupling, it may not respond tocommands at idle due to the lower pumpingeffect inside the coupling at low controlling the EV Cooling fan, it isbest to have the engine at 2,000 rpm toensure that there is enough fluid movementto fully engage and disengage the on engine temperature and rpm,there may be a delay of up to 2 minutesbefore hearing the fan respond to your Tech2 command.

9 The lower the engine speed,the longer it will take. In lower ambienttemperatures, the Cooling fan will engage inless time, but will take longer to disengagedue to properties of the Controlled Viscous Cooling Fan continued from page 1 Other Diagnostic TipsIf there are related fan DTCs (typically aP0495) and the EV Cooling fan cannot becommanded off using the above method, astuck EV Cooling fan may be isolated byunplugging the EV fan connector on theradiator shroud and running the engine at2,500 for two Cooling fan should return to an unlockedstate under these conditions. If you cannot hearthe fan disengage, the coupling is stuck design characteristic of the fan couplingmay cause the fan to be temporarily engagedafter a cold start. If the coupling was lockedup during a previous drive cycle due to A/Cpressure, transmission temperature, orengine temperature, some cold start fannoise may be normal. The fluid coupling doesnot disengage overnight and the silicone fluidin the coupling will be thicker when , if the vehicle is parked for anextended period, the fluid may migrate fromthe reservoir into the coupling, resulting infan operation even though the engine is the fan is commanded OFFduring a cold start, the fan may be engagedfor these reasons.

10 This is the most likelytime a customer will notice and comment onexcessive fan Fan NoiseA fully-engaged fan can generate a lot ofnoise. Comparing a noise complaint to a likevehicle can be difficult, and the conditionsfrom vehicle to vehicle may be questioning the customer about afan concern, get specific information: Were you using the A/C or defroster onthe previous trip? Was the ambient temperature high thelast time the vehicle was driven? Was the vehicle driven an extendedperiod of time the last time? Was the vehicle parked for an extendedperiod before the noise concern?These conditions can all cause a highnoise concern, because the EV clutch cantake up to 2 minutes to noise may be mistaken for a high idle,loss of power, transmission slip, or delayedtransmission shift. If you receive a concernlike this that cannot be verified and there areno related DTCs, it may help to take a testdrive with the customer. Command the fanon to determine if they may be mistakingnormal fan noise for a malfunction.