Subaru 4EAT Transmissions
Subaru 4EAT Transmissions
Overview Fea eatures tures and M aj ajor or Compo Components nents Power Pow er Flow Flow Final Drive Dri ve FW FW D/AW D/AWD D Ele lectronic ctronic Co Control ntrol System Hydraulic Co Control ntrol System Self Diagnostic System Troubleshooting/Adjustments
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he 4EAT Transm ission is a 4 sp eed, m icroprocessor-controlled tra nsm ission that w as first introd uced in 1987.5 Subaru m odels. It is not a 3 sp eed tran smission w ith overd rive. It features a lock-up torque converter which locks up in all forward gears except 1st. It has been offered in FWD or Full Time AWD configur ations. The 4EAT transmission has undergone continuous development an d improvement since its introduction. Several u niqu e 4EAT features hav e been O v e r v i e w add ed, changed, or deleted from various Subaru m odels over th e years. We’ll provide you w ith a brief overview of these features here. For a more th orough description of sp ecific 4EAT operating characteristics or features, refer to the a pp licable Subaru service manual for the year and mod el Subaru you are working on. Some Subaru mod els were equipped with a 1-HOLD bu tton. These includ e: • 1987.5-91 XT and XT6 models • 1988-89 “L” series • 1990 Loyale Shift Quadrant Manu al 1st gear is activated wh en the 1-HOLD button is d epressed and the shifter is in manu ally selected “2” to p rovide engine braking. The transm ission w ill upsh ift throu gh 2nd and 3rd if necessary, in ord er to preven t the engine from over-revving. The 1-HOLD indicator is displayed on the combination meter wh en the bu tton is activated. When the comp uter overrides the 1-HOLD gear selection the d isplay will chan ge. Some mod els have a POWER light located to th e left of the tachometer (right on Legacy). It is activated momentarily whenever the vehicle is started. The POWER mode is selected by the compu ter based u pon how qu ickly the gas pedal is dep ressed. This changes th e perform ance characteristics of the tran smission. i.e., it delays upshifts and may downshift if necessary. When selected, the computer turns the POWER light “ ON.” An enh anced v ersion of the original 4EAT wa s introdu ced with th e 1990 mod el year Legacy. Althou gh similar in d esign to the or iginal 4EAT, the shift quad rant is d ifferent. The Legacy 4EAT has a seven p osition qu ad ran t: P-R-N-D-3-2-1. The 1HOLD button has been deleted and a m anual button was add ed. Subaru vehicles equipped w ith the manu al button includ ed: • 1990-94 Legacy • 1993-94 Imp reza • 1992-97 SVX When the selector is in 3rd range with the m anual sw itch “ON ,” the transmission will start in 2nd gear a nd shift to 3rd. In 2nd ran ge man ual, the transm ission starts and stays in 2nd gear, but w ill up shift to 3rd gea r at 6500 RPM to prev ent dam age to the engine. In 1st range man ual the transmission stays in 1st gear and also will up shift to second at 6500 RPM to prevent d ama ge to the engine. Add itionally, on AWD vehicles, the TCU ap plies a m ore aggressive AWD map wh en the selector is in th e 1st position, manu al switch “ON ” or “OFF.” These changes result in improv ed d riveability on low friction road surfaces. The TCU monitors variou s engine an d v ehicle inpu ts, i.e., throttle position and vehicle speed, etc. It also controls the electronic shift solenoid s in th e tran smission. Refer to the ap prop riate mod el year Suba ru serv ice man ual, section 6-3, for the location of the TCU.
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Selector Lever
TCU
MPT Assembly
MPT Clutch
MPT Clutch Hub
Reduction Shaft Seals
Transfer Clutch A sse mbly (AWD) The transfer unit consists of a hydraulic multiplate clutch and a hydraulic control system incorporating a d uty solenoid . It is housed in the extension case at the rear of the transmission. A caged needle bearing su pp orts the clutch on th e reduction d rive shaft and a ball bearing su pp orts the clutch in the case. Duty solenoid “C” regu lates the MPT clutch. It is controlled b y the TCU wh ich determines the d egree of AWD by altering the d uty ra tio. As the d uty ratio increases, the am oun t of AWD decreases. The clutch itself, features friction d iscs tha t are d esigned to slip. This eliminates torque binding d uring tight cornering. In order to get pow er to the front wheels, the reduction gear powers the reduction d riven gear which is attached to the drive pinion shaft. For the rear wheels, power goes from the reduction drive shaft to the MPT clutch hu b wh ich is welded to the drive gear. The power is transferred through the MPT clutch where it outputs to the rear drive shaft. Reduction sha ft seal rings d irect fluid from the hollow sh aft to the lubrication circuits inside the tran smission.
MPT Power Flow
4EAT Transmissions Electronic Control System Overview The electronic control system consists of various inp uts (sensors) and ou tpu ts (lights an d solenoids) in ad dition to th e Transm ission Con trol Unit (TCU). This is the next generation of Subaru au tomatic transm ission. In add ition to being smoother and quieter, it is designed to help maximize fuel economy while providing p erformance. It monitors the engine and transmission performance conditions, the drivers deman ds and the vehicle speed. Transmis sio n Control Unit The TCU is a highly sop histicated m icroprocessor with a self diagn ostic long term m emory. It also has a fail safe function w hich ma intains d riveability in case of a ma jor electrical compon ent failure. In a transmission equipped for AWD the TCU utilizes a program which continually changes th e degree of AWD based upon vehicle operating condition(s). The TCU controls shifting an d line pressu re in add ition to the lock-up torque converter and the MPT clutch. TCU Inputs • Throttle sensor/ idle switch • Vehicle speed sensor #1 • Vehicle speed sensor #2 • Tachometer signal • Inhibitor switch • Cruise control signal • ATF temperature sensor • Ignition/ battery voltage • 1-HOLD switch (if so equipped ) • Forced FWD
TCU Locati on
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Subaru 4EAT Transmissions Trans mis sio n G ear Train This comp act unit features a dou ble planetary gear set. It has a wide ratio between gears for improv ed fuel efficiency as well as high p erformance. Transaxl e Gear Train
Rear Sun/Rear Carrier
Rear Gear Set
Gear Train Components Front sun gear Front planetary carrier Rear sun gear Rear planetary carrier (front internal gear) Rear internal gear Operating Principals: Rear Gear Set The rear sun gear is always p owered by th e input sh aft. The rear planetary carrier always transmits pow er to the outpu t shaft. The one way clutch (O.W.C.) 3-4 preven ts the rear intern al gear from tu rning cou nterclockwise. Its inn er race is the rear internal gear and its outer race is the forward clutch hub. The overrunning clutch hub is also connected, by dogs, to the rear internal gear. The overrunning clutch p rovides engine braking d uring deceleration except in D-1 and 3-1. The O.W.C. 3-4 is used in 1st, 2nd, and 3rd gears. The forward clutch is used in all forward gears. The rear internal gear is controlled b y the forward clutch through the O.W.C. 3-4. Additionally, the rear internal gear is controlled by the overrun ning clutch. The forw ard clutch connects the rear internal gear to the front planetary carrier (splined to the forwa rd clutch d rum ) through the O.W.C. 3-4. The overrunning clutch is also used to connect the rear internal gear to the forward clutch drum and the front planetary carrier. The O.W.C. 1-2 (Spr ag) prev ents th e Overrunning Clutch Hub forward clutch drum from rotating counterclockw ise. The Spra g is app lied w hen the transmission is operating in D-1 or 3-1. The Low/ Reverse brake is splined to th e case. It holds the forward clutch dru m in order to keep it from turning w hen One Way Clutch 1-2 the tra nsm ission is in Reverse, 2-1, and 1-HOLD (if so equppped).
Front Sun Gear
Front Planetary Carrier
Rear Sun Gear
Rear Planetary Carrier
Rear Internal Gear Forwar d Clutch Drum
Low/Reverse Br ake
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Overrunning Clutch Hub Installed
Operating Principles: Front Gear Set The high clutch dru m (reverse clutch h ub) is splined to the inp ut sh aft. It supplies power to the reverse clutch and the high clutch. The high clutch hub is splined to th e front p lanetary carrier. When the reverse clutch is app lied for Reverse gear it powers the front sun gear. When th e high clutch is applied in 3rd and 4th gear it powers the front planetary carrier via the high clutch hu b. The front sun gear is dogged to the reverse clutch drum. The front planetary carrier is splined intern ally to the high clutch hub a nd it is splined externally to the forward clutch dru m.
One Way Clutch 3-4
Rear Internal Gear
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Reverse and High Clutches
Front Gear Set
Band Servo Op eration The band is app lied in 2nd and 4th gears by a tw o stage servo wh ich is controlled by accumulators. In order to obtain second gear the servo is in the 2-App ly mode. Hyd raulic pressure from the 2A accum ulator pushes the 1-2 piston UPWARD which tightens the ban d. For third gea r, the servo is in the 3-Release mod e. In th is case, hydraulic pressure from the 3R accumulator aided by the return spring pushes the 1-2 piston DOWNWARD in order to release the band . Band and Servo For fourth gear 4-Apply mode, hydraulic pressure from the 4A accumu lator push es the 3-4 piston UPWARD in order to apply the band.
Servo Operation I (later 4EAT models)
Power Flow
Application Chart
Power Flow: D-1
Power Flow: D-2
Power Flow: D-3
Power Flow: D-4
D-1 or 3-1 Operating Mo de The input shaft powers the rear sun gear clockwise. When the Forward clutch is app lied, the O.W.C. 3-4 outer race (forwa rd clutch hub) is attached to the front carrier. With the O.W.C. 3-4 operating , the rear internal gear can on ly go clockwise. With the O.W.C. 1-2 operating, the forw ard clutch dru m can only go clockwise. Outpu t power is through the rear carrier and the outpu t ratio is 2.785:1. During coast mod e, the O.W.C. 3-4 is released and there is no engine braking. D-2, 3-2, Or 2-2 Operating Mode Again, the input shaft powers the rear sun gear clockwise. When the forwa rd clutch is ap plied, the O.W.C. 3-4 outer race (forw ard clutch h ub) is attached to th e front carrier. The ban d is also applied which holds the front sun gear stationary. Output power is transmitted from the rear carrier (front internal gear) w here the outp ut r atio is 1.545:1. During the coast m ode, the O .W.C. 3-4 is released and there is no engine braking. D-3, 3-3 Operating Mo de The input shaft powers the rear sun gear clockwise. When the forward clutch is app lied, th e O.W.C. 3-4 outer race (forward clutch hu b) is attached to th e front carrier. The h igh clutch is also app lied and the front planetary carrier is therefore powered. In this case the planetary gear set is locked u p an d th e outpu t ratio is 1:1. During the coast m ode, th e O.W.C. 3-4 releases the rear internal gear and there is no engine braking. D-4 Operating Mode The input shaft powers the rear sun gear clockwise. When the forward clutch is ap plied it d oesn’t affect the p ower flow. It freewh eels through the O.W.C. 3-4. When th e high clutch is app lied, the front plan etary carrier is pow ered clockwise. Since the band is applied, the front sun g ear is held stationary. The outp ut is clockwise through the front internal gear (rear planetary carrier) and the ou tpu t ratio is 0.694:1. Engine braking occurs d uring the coast and deceleration mod es. Neither O.W.C. is used .
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Servo Operation II (later 4EAT models)
Subaru 4EAT Transmissions 2-1 and 1-HOLD Ope rating Mod es The pow er flow is the sam e as in the other 1st gears except as follows. The rear internal gear is held by th e overrun ning clutch instead of by the O.W.C. 3-4. In ad dition, the forw ard clutch dru m is held b y the Low/ Reverse brake instead of the O.W.C. 1-2. Engine braking occurs du ring coast and deceleration d ue to conditions described above. The overrunning clutch is “ON” and the Low/ Reverse brake is “ON.”
Power Flow: 1-Hold
Reverse Operating Mode When the reverse clutch is applied the front sun gear is pow ered. The Low/ Reverse brake is also app lied, which holds the front plan etary carrier stationary. Ou tpu t pow er is through the rear carrier at the ratio of 2.272:1. Gear Train Components Front sun gear Front planetary carrier Rear sun gear Rear planetary carrier (front internal gear) Rear internal gear
Power Flow: Reverse
Subaru
Final Drive FWD/AW D Differential Overview The hypoid gear set is mou nted in the aluminum torque converter case. It is supported by taper roller bearings and features removable stub axle shafts. The pinion is mounted th rough the oil pu mp h ousing.
Differential Housing
Oil Pump Housing
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Oil Pump Housing Features The housing is made of cast iron for greater rigidity. Double taper roller bearing s are used to supp ort the pinion. This allows for the thermal expansion of two dissimilar metals: aluminum and cast iron. These bearings also improve the du rability and reliability of the unit. The pinion is preload ed by a locknu t wh ich allows for easy serviceability. Pinion depth is set by shims which are located between the bearing flange and the oil pump housing. A dou ble-lip oil seal separates transm ission fluid from the hypoid gear oil. This greatly imp roves th e fluid system reliability. Differential Carrier Features The ring gear is mou nted on the right sid e of the carrier. This design ad ds to its compa ctness and makes it easier to service. The backlash is easily ad justable through the carrier bearing retainers. Final drive ratios have gone through several changes in the year s since the 4EAT was originally introd uced on 1987.5 models. For accurate final drive ratio information, refer to Differential Carrier the ap plicable Subaru service man ual.
Oil Pump Cover Seals
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MPT Assembly
MPT Clutch
MPT Clutch Hub
Reduction Shaft Seals
Transfer Clutch A sse mbly (AWD) The transfer unit consists of a hydraulic multiplate clutch and a hydraulic control system incorporating a d uty solenoid . It is housed in the extension case at the rear of the transmission. A caged needle bearing su pp orts the clutch on th e reduction d rive shaft and a ball bearing su pp orts the clutch in the case. Duty solenoid “C” regu lates the MPT clutch. It is controlled b y the TCU wh ich determines the d egree of AWD by altering the d uty ra tio. As the d uty ratio increases, the am oun t of AWD decreases. The clutch itself, features friction d iscs tha t are d esigned to slip. This eliminates torque binding d uring tight cornering. In order to get pow er to the front wheels, the reduction gear powers the reduction d riven gear which is attached to the drive pinion shaft. For the rear wheels, power goes from the reduction drive shaft to the MPT clutch hu b wh ich is welded to the drive gear. The power is transferred through the MPT clutch where it outputs to the rear drive shaft. Reduction sha ft seal rings d irect fluid from the hollow sh aft to the lubrication circuits inside the tran smission.
MPT Power Flow
4EAT Transmissions Electronic Control System Overview The electronic control system consists of various inp uts (sensors) and ou tpu ts (lights an d solenoids) in ad dition to th e Transm ission Con trol Unit (TCU). This is the next generation of Subaru au tomatic transm ission. In add ition to being smoother and quieter, it is designed to help maximize fuel economy while providing p erformance. It monitors the engine and transmission performance conditions, the drivers deman ds and the vehicle speed. Transmis sio n Control Unit The TCU is a highly sop histicated m icroprocessor with a self diagn ostic long term m emory. It also has a fail safe function w hich ma intains d riveability in case of a ma jor electrical compon ent failure. In a transmission equipped for AWD the TCU utilizes a program which continually changes th e degree of AWD based upon vehicle operating condition(s). The TCU controls shifting an d line pressu re in add ition to the lock-up torque converter and the MPT clutch. TCU Inputs • Throttle sensor/ idle switch • Vehicle speed sensor #1 • Vehicle speed sensor #2 • Tachometer signal • Inhibitor switch • Cruise control signal • ATF temperature sensor • Ignition/ battery voltage • 1-HOLD switch (if so equipped ) • Forced FWD
TCU Locati on
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Subaru 4EAT Transmissions Legacy TCU Inp uts The Legacy fuel system ECM, beginning w ith mod el year 1990, sends n ew inpu ts to the TCU for line pressu re control. It networks the MPF1 ECU RPM and altitude compensation inputs. This provides additional line pressure control for high altitude compensation to reduce shift shock. ABS system inpu ts turn “OFF” the over-run ning clutch w hen ABS is active and fixes the d uty ratio of the MPT clutch (mostly FWD). • ECM RPM • Altitude compensation • ABS system Throttle Sensor The throttle sensor/ idle switch is basically electrical throttle pressure. The load signal effects: shifting, line p ressure a nd lock-up . The closed th rottle inpu t effects the lock-up release mode as w ell as smooth d own shifting into 2nd gear. It also causes a reduction in line pressure. Throttle Sensor
Vehicle Spe ed Sen sor #1 Vehicle speed sensor #1 is mounted to the transmission and is basically electrical govern or pressu re. It is used to detect vehicle speed an d it effects shift points, lock-up, and line pressure. In FWD transmissions the speed sensor reads parking gear rotation at the front outp ut sha ft. In AWD transm issions it senses the transfer clutch d rum rotation at the rear outpu t shaft. Speed Sensor #1
Vehicle Spe ed Sen sor #2 Vehicle speed sensor #2 is bu ilt into the com bination m eter. In FWD un its, it is used as a back-up for speed sensor #1. In AWD un its, it is used as the front outp ut shaft speed sensor. TCU The TCU compares the speed signal from the front output shaft with the signal from the rear ou tpu t shaft (sensor #1).The speed differential helps the TCU determ ine the deg ree of AWD (along with other inp uts).
Combination M eter
Tachometer The tachometer signal effects the shift points at kickdow n. The TCU uses the signal to prevent the engine from over-revving. Inhibitor Switch The inhibitor switch is located on the right side of the transmission. It is operated by the gear sh ift lever which controls the linkag e that op erates the man ual valve. It signals the TCU of the selected gear ra nge, wh ich w ill then control the shift points and ad justs the line pressu re according ly. NO TE: THE TCU WILL OVERRIDE THE INHIBITOR SWITCH, IF NECESSARY, IN OR DER TO PREVENT THE ENGINE FROM OVER-REVVING.
Inhibitor Switch
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Cruise Control Si gnal The cruise control signal tells the TCU of cruise control activation. This allows for a wider operating range in 4th gear unless a large speed d ifferential exists fro m th e set speed in w hich case the transmission may Cruise Control downshift. This improves fuel economy. The ATF temp erature sen sor is located on th e lower valve body next to duty solenoid “B.”
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When the ATF is cold, th e TCU w on’t allow an up shift into 4th gear. The object is to warm the engine qu ickly for lower em issions. It is more soph isticated than the KDLH system and less objectionable for the consu mer. ATF Temperature Sensor When the ATF is hot (AWD only), the TCU sh ifts the transm ission a s if in the POWER mode. This pushes the shift points higher which allows the engine to run faster. The oil pu mp then circulates ATF through the oil cooler mo re quickly so as not to overheat the engine coolant.
Temp Sensor
System Voltage The TCU also mon itors system voltage in order to correctly interpret the inp uts and alter the control of the outp uts. For examp le, the system is designed for 12 volt operation. When ru nning, how ever, most veh icles have other than 12 volts available. The 1-HOLD sw itch is located aft of the shift quad rant. When activated, it creates a forced 1st gear. NO TE: THE TCU W ILL SHIFT 2ND TO 3RD IF NECESSARY, IN O RDER TO PREVENT THE ENGINE FROM OVER-REVVING.
Forced FWD Switch The FWD switch chang es the driving m ode from AWD to FWD, and sh ould b e used for diagnostic pur poses only. Do not d rive the vehicle in this mod e. The FWD switch is located on the left front shock tow er. The Legacy FWD switch is located on the right stru t tower. It is activated by inserting the sp are fuse into the un derhood connector. The FWD light on th e combination m eter verifies that th e vehicle is in FWD. Maintenance Precautions Before jacking up one or two wheels for maintenance with the engine running or before runn ing the veh icle on a chassis d ynom ometer, the electronic AWD engagem ent system MUST be diseng aged by installing the spa re fuse (15A) of the fuse box into the FWD connector located u nd er the hood . Failure to do so could result in movem ent of vehicle. (Refer to owner ’s man ual.)
Shift Quadrant
Forced FWD Swit ch
TCU Outputs There are two types of outp uts; solenoid controls and light controls. The solenoids control shifting, line p ressure, lock-up and AWD. The light controls ind icate oper ating cond itions to the dr iver. They ind icate the POWER mod e, man ually selected 1st or 2nd gear, or hot ATF (AWD on ly). On th e 1990 mod el year and later Legacy mod els the light controls indicate hot ATF (FWD an d AWD), gears 3 - 2 - 1, MANUAL mod e, and POWER mode. Shift solenoids #1 and #2 are located on th e up per v alve bod y. The TCU induces “ON/ OFF” conditions which regulate the shifting of the forward gears. When a shift solenoid is “ON ,” it passes pilot pressure to sh ift valve “A” and / or shift valve “B.” The valve(s) will then shift, feeding th e app ropriate controlling m ember circuits (high clutch, ban d, etc.). Power Lamp
NO TE: PILOT PR ESSURE IS NOTHING MO RE THAN A PRESSURE HELD AT A CON STANT VALUE.
When a shift solenoid is “ OFF,” the affected shift valve w ill move to its static position due to spring pressure. The appropriate controlling member circuit will then be fed (high clutch, band , etc.).
Shift Solenoids 1and 2
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Subaru 4EAT Transmissions Shift Modes
Solenoid Application Chart
Shift Solenoid #3 Shift solenoid #3 is located on the u pp er valve bod y. It is used to control dow nshifts. It quickly releases the 3-Release pressure d uring low sp eed h eavy load situations in order to provide smooth 3-2 downshifts. It operates the overrunning clutch in order to provide engine braking during deceleration. It is also used to cancel the overrunning clutch momentarily during light throttle 3-2 downshifts, or closed throttle 2-1 dow nsh ifts. This redu ces the shift shock. Duty Solenoid “A” Duty Solenoid “A” is located on the u pp er valve body. It regulates line pressure at three levels: • Basic: Altered with load , vehicle speed, and range signa l. • Shifting: Lowers line pressure in betw een shifts to minimize shift shock. • Start up : With low ATF temperatu re or a low tach signal [cranking sp eed], it sets line pressure to a minimum.
Shift Solenoid 3
Dropping Resistor The drop ping resistor is wired in par allel with du ty solenoid “A,” and is used to regulate line pressure. It is located on th e right front shock tow er behind the MPI fuel system d ropp ing resistor. It takes over line pressure control du ring the “OFF” portion of the d uty cycle for the d uty solenoid . In other w ords, the d uty solenoid is never fully “OFF.” Du ty Solenoid “B” Duty Solenoid “B” is located on the lower v alve bod y next to the ATF tempera ture sensor. It opera tes the lock-up clutch in 3 mod es: “ON ,” “OFF,” and a gradu al “ON/ OFF” control of the lock-up clutch during gear shifting in order to redu ce shift shock.
Duty Solenoid “ B”
Dropping Resistor
Du ty Solenoid “C” Duty Solenoid “ C” Duty Solenoid “C” is located in the extension hou sing. It is also controlled by th e TCU. It varies the degree of AWD. Powe r Indicator Light The POWER Indicator Light is located in th e combination meter. It is activated mom entarily wh enever th e vehicle is started as part of the self check system. It turns “ON” when the TCU selects the POWER mode with the vehicle in the “D” range. It blinks a self diagn ostic code wh enever the TCU is programm ed for self diagnosis. The TCU monitors the th rottle angle opening speed , i.e., how qu ickly the gas pedal is depressed. When a predeterCombination M eter mined rate is exceeded , the POWER mod e is activated. NO TE: THERE ARE A NUMBER O F PREDETERMINED R ATES BASED O N THE VEHICLE SPEED VS. THRO TTLE ANGLE RELATION SHIP. THESE DETERMINE EASE OF ACCESS TO PO W ER MOD E. AS A GENERAL RULE, IT IS EASIER TO ACTIVATE THE
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POW ER MODE AT LOW ER SPEEDS FRO M A LIGHT THROTTLE THAN IT IS AT HIGHER SPEEDS FRO M A LIGHT THROTTLE.
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The POWER mod e increases the u pshift and dow nshift points. It is deactivated by the v ehicle speed and the throttle angle, i.e., if the speed is equal to or g reater than a pp roximately 40 MPH with a light throttle, deactivation is immed iate. If the sp eed is less than a pp roximately 40 MPH, a time lag of up to 3 second s will occur before resum ing the nor mal shift pattern. 2nd Ge ar Indicator The 2nd Gear Ind icator is located with th e shift position indicators. It is controlled by th e TCU. Other qu ad rant ind icators are controlled by th e inhibitor switch. The 2nd g ear ind icator is affected by th e 1-HOLD switch inpu t. The TCU grounds the 2nd gear indicator light with the 1-HOLD switch “OFF” and the shift lever in “2” (except Legacy). 1-HOLD Indicator Light (if so equipped) The 1-HOLD indicator light (“L,” Loyal an d XT only) is located n ear the combin ation m eter shift position ind icator. It is activated by the TCU when ever the 1-HOLD button is d epressed w ith the shift lever in “2.” It chan ges the disp lay and cancels the “2” indicator. The vehicle stays in 1-HOLD unless the TCU d etermines a p otential engine over-rev condition, at which point, the tran smission will then upshift. NO TE: WHEN 1-HOLD IS ACTIVATED, ALL OTHER SHIFTING INP UTS ARE IGNORED.
Beginning in the 1990 mod el year Legacy, the 1-HOLD button and Combination Meter Display light have been deleted and a MANUAL switch and light add ed. When the transmission is in 3rd ran ge, MANUAL switch “ON ,” it locks out 1st gear and sh ifts 2-3. When in 2nd range MAN UAL, the tran smission locks out 1st gear and is held in 2nd gear (until 6500 RPM when it will up shift to prevent engine dam age). When in 1st range MAN UAL the transmission is locked in 1st gear (until 6500 RPM when it will up shift to prevent engine d ama ge). NO TE: TCU WILL ALWAYS OVERRIDE THE SELECTOR PO SITIO N AT 6500 RPM .
ATF Temperature Warning Lamp An ATF Temp erature Warning Lamp is provid ed for “L” Series and XT (AWD only) and for the Legacy (FWD and AWD). The lamp is located on the combina tion meter. It is activated by th e TCU to ind icate overheated ATF fluid. The TCU w ill shift the transm ission as if in the POWER mod e to help red uce the ATF temperatu re.
Hydraulic Control System Valve Body The valves and solenoids control the lubrication circuits, the lock-up torque converter, shifting, etc. The valve bod y is divided into two m ajor sections: upp er and lower. The valve body w orks in conjun ction w ith the TCU. It is designed to provid e smooth sh ift control and comp onent longev ity. It also reduce un necessary high pressu re in certain instances. As an examp le, line p ressure is lowered between shifts. The valve body featu res shift step control. This means that gea r mem bers are momentarily applied between shifts it allows them to be brought u p to speed which reduces shock.
Valve Body
Upper Valve Body
Lower Valve Body
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Subaru 4EAT Transmissions Accumulators There are four accumulators mounted in the transmission case: • 4-App ly (4A) • 2-App ly (2A) • 3-Release (3R) • Neutral/ Drive (ND)
Accumulators
Acc umulator Operation
They are designed to lessen shift shock by absorbing the su dd en pressure change generated when a circuit is activated. This ensures smooth component application. The accumulator resistance will vary in direct proportion to the line pressure. Accumulators normally operate at a fixed rate in other automatic transmissions. Therefore, as the transmission pressu res rise, the accumu lator cannot further compensate du e to the constant value of the spring. Pressure shocks are thus transferred to the components. In the 4EAT Accumu lators, however, the line p ressure is app lied to th e back of the accum ulator p iston. Therefore, the resistance to pressure is p roportiona lly increased hyd rau lically. This keeps the p ressure shock un der control, allowing smoother component app lication. An ad ditional accumu lator is located in the lower section of the valve body, next to the m anual valve. It absorbs line pressure pulses created by the sud den changes in line pressure. NO TE: THE 4EAT IS A HIGHLY RELIABLE TRAN SMISSIO N. SHO ULD AN ELECTRICAL COM PO NENT MALFUNCTION , HOWEVER, IT WILL ALWAYS FAIL SAFE FOR “LIMP HOME.”
Fail Safe Components And Failure Results If a speed sensor fails, the remaining sen sor signal will be used . In case of throttle sensor failure, the idle contacts w ill signal the th rottle openin g. Line p ressure w ill go to maximum at open throttle and it will go to minimum at closed throttle. Althoug h the inh ibitor switch m ay fail, the manu al valve will still be in the correct position for all selected ran ges. In “P” and “N” how ever, it may effect start-up , therefore, there is a poten tial for a no-start cond ition. In Reverse, the TCU is pa ssive. Therefore, an inh ibitor switch failure h as n o effect. If mu ltiple signals are seen in the forward ranges the inhibitor switch is ignored and there is no fourth gear. If the 1-HOLD switch is defective, the system opera tes in the sam e man ner as an inhibitor switch failure in the forward ranges. If the MAN UAL switch is d efective (Legacy only), the transm ission w ill shift norm ally in D position. It will operate the sam e as wh en there is an inhibitor switch failure w hen the tran smission is in selector position 3 - 2 - 1 . If shift solenoids #1 or #2 malfun ction, the TCU deactivates th e other. This results in either 3rd gear or Reverse (wh en selected). If du ty solenoid “A” fails, line pressu re goes to maximum . If duty solenoid “B” fails, the torqu e converter lock-up w ill not occur. If shift solenoid #3 malfunctions, the overrun ning clutch is always “ON ” and there will be engine braking during deceleration. If du ty solenoid “C” sh ould fail, the AWD control will be set to maximu m an d the rear wheels will always be pow ered.
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Self Di agnostic System The 4EAT self diagn ostic system ha s three mod es: a user mod e and tw o dealer modes. In the first instan ce, the u ser is notified throu gh the POWER light wh en a m alfunction occurs. The failure is commu nicated after the n ext ignition “OFF/ ON” cycle. For a more detailed description of the user m ode, see the app ropriate troubleshooting section of the service manu al. Shift Quadrant
NO TE: THE SYSTEM W ILL FAIL SAFE FO R “LIMP
Combination M eter
HOME.” WHEN A COM PO NENT FAILS, THE LIGHT WILL NO T LLUMINATE UNTIL THE IGNITION IS SWITCHED “O FF” AND THEN SWITCHED TO “ON” AGAIN.
For specific information on th e self diagnostic dealer mod es, see the appropriate troubleshooting section of the service manual. The Select Monitor requires the specific 4EAT cartridge to perSelect Monitor form the analysis. This form of analysis is the preferred troubleshooting/ self-diagnostic method . The Select Monitor iden tifies curren t problems, p ast problems (throu gh long-term memory), and indicates actual circuit and component performance. It also allows data to be observed under actual driving conditions which is of great assistance in the d iagnosis of intermittent p roblems. The Select Monitor ha s four ma jor mo des: Function mo des (15) These mod es indicate sensor and componen t performance data and are disp layed on th e LED screen. Examp le: Mode F 01 = F 01 12.6 volts (Batter y vo ltage)
“A” modes (3) These mod es indicate the operation of 13 different switch inpu ts wh ich are displayed by the red n um bered LEDs. - LED “ON” = switch “ON ” - LED “OFF” = sw itch “OFF” Functions of the red LED’s are identified by letter code on th e up per screen.
“B” modes (2) These two modes display the current TCU self-diagnostic codes and the past TCU self-diagnostic codes (long-term m emory). NOTE: WHEN USING SELECT MONITOR IN THE “B” MODES IT IS NOT NECESSARY TO PERFOR M THE NO RMAL SELF-DIAG NO STIC ACCESS PROCEDURES.
“C” mode (1) This clears the trouble codes th at are stored in lon g-term mem ory. NO TE: REFER TO THE APP RO PRIATE SERVICE MA NUA L , SECTION 3 - 2, AND R EVIEW SELECT MONITOR USAGE AND TROUBLESHOOTING PROCEDURES.
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Code Inter pretation
Subaru 4EAT Transmissions
Subaru 4 Cable Adjustment
Troubleshooting/Adjustments Prelim inary Inspection Check the following : Fluid level ATF leaks Road Test: • Check proper shift points • Engine performance Correctly ad justed throttle sensor Gearshift cable adjustmen t Correct stall test results Inhibitor switch connections Correct pressure test results
Inhibitor Switc h/Cable
Inhibitor Switch/Adjustment
Gearshift Cable Adjustment Place the transmission in neutral with the engine “OFF.” Then loosen the locking nut an d the ad justing nut. Push th e shift lever arm rearward and tighten the ad justing nu t u ntil it contacts the conn ecting block. Finally, secure the cable w ith the locking nut and dou ble check the operation. After adjusting th e gearsh ift cable, verify the correct inh ibitor switch position. Remove the cable from the inhibitor switch in order to perform the adjustment. The switch m ust be in neu tral. Then insert the sp ecial tool #499267300 Stopp er Pin th rough the 2 levers of the switch into the d epression in the sw itch bod y. Next, loosen the 3 retaining bolts and rotate the inh ibitor to adjust. Finally, reinstall the cable and reconfirm the cable adjustment. Stall Test The stall test checks the operating condition of the AT clutches, the torque converter, and the engine. Perform these checks in “D,” “3,” “2,” and “Reverse.” Stall Test Res ults High er than n ormal RPM indicates one or more of the following: • Slipp age of the forward clutch • O.W.C. not hold ing • Low/ Reverse brake slipping • Overall low line pressure Lower than norm al RPM indicates one or more of the following: • Incorrect throttle adjustment • Poor engine operation • Torque converter stator slipp age
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AT Transmissions Time Lag Test The time lag test checks the operation of the forwa rd clutch, the reverse clutch, the low / Reverse br ake, O.W.C. 3-4, and O.W.C. 1-2. Perform this test at operating tem pera ture. Idle the engine w ith the A/ C “OFF.” Confirm the p roper id le speed in “ N” and correct if necessary. Then sh ift into “D” and measure the time (seconds) to full engagement. It should take less than 1.2 seconds. Then shift into “R” and measu re the time. It shou ld take less than 1.5 seconds. Time Lag Resul ts: If the time takes longer from “N” to “D” it may ind icate one or m ore of the following: • Low line pressure • Worn forward clutch • O.W.C. problem
Pressure Test Port
If the time takes longer from “N” to “R,” it may indicate one or m ore of the following : • Low line pressure • Worn reverse clutch • Worn low/ rev brake Pressure Test This is a preliminary test which should be conducted prior to any disassembly. Perform a pressure test when all the circuits show evidence of slippage or when the circuits show negative resu lts from th e time lag test. This test shou ld also be performed if there is excessive shift shock, delayed shifting, or if the vehicle is immobile. Perform th is test by connecting the pressure gauge to the “oil pum p outlet” test port in order to determine the overall line pressure. Should a particular component be suspected, perform pressure tests at its unique test p ort. Refer to the Service Manu al, Sec. 3-2 for other por ts. Check for minim um and maximum values at each port. On Car Service/Adjus tments The following can be performed on the veh icle: • Checking/ changing fluids • Band ad justment • Valve body servicing • Shift linkage adjustment/ replacement • Inhibitor switch adjustment/ replacement • Harness repair/ replacement • Transfer clutch assembly (servicing/ replacement) • Speed sensors replacement
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MPT Test Port