Functional Descriptionof TCU Transmission Control Unit Wanted

[JimFierst]

Is there anywhere on line I could look at a description of the functions of the TCU for a 2000 legacy Outback.? I am looking to get the source of the TCU's inputs and the action it takes. I am aware that the TPS sends throttle positions and the TCU causes up shifts and down shifts.

[porcupine73]

Howdy, here's some info. Unfortunately there are also a lot of good diagrams and charts that don't show up here.

 

Transmission Control Module (TCM)

TCM receives various sensor signals and dictates the running conditions of the vehicle. It sends control signals to each solenoid according to the preset gearshift characteristic data, lockup operation data, and transfer clutch torque data (duty ratio).

 

A: CONTROL SYSTEM

 

B: SYSTEM DIAGRAM

 

C: SHIFT CONTROL

Gearshifting is controlled in response to driving conditions, according to the shift point characteristic data stored in the TCM. Solenoids are operated at the proper time according to the shift pattern, throttle position, and vehicle speed for smooth shifting.

 

NOTE: When oil temperature is below approximately 10°C (50°F) , the vehicle cannot be shifted to the 4th gear.

 

Control module activates both solenoids 1 and 2 in response to throttle and vehicle speed signals.

Shift valve moves in response to solenoid operation, supplying/interrupting clutch pressure to the line.

Gears are shifted by ON-OFF operation of both solenoids as indicated.

D: LOCK-UP CONTROL

The lock-up engaging and disengaging conditions are set for 4th gear shift range, gear position and shift pattern and correspond to the throttle position and vehicle speed, and the duty solenoid electronically controlled by TCM controls the lock-up clutch. The lock-up clutch engagement and disengagement are controlled by the lock-up control valve.

 

The lock-up control valve engages and disengages the lock-up clutch by varying the hydraulic pressure.

 

Non-Lock-Up Operation

The Transmission Control Module (TCM) sends output signals to the lock-up duty solenoid. This causes the amount of ATF drained from the lock-up duty solenoid valve to be reduced, which increases the lock-up duty pressure.

The increased lock-up duty pressure moves the lock-up control valve upwards, connecting the torque converter regulator valve to the torque converter control valve release port.

Therefore, the oil pressure from the torque converter regulator valve flows through the lock-up control valve release port to the torque converter clutch and the torque converter apply circuit. As a result, the lock-up piston is forced to separate from the impeller cover, and power is transmitted from impeller to turbine to input shaft, as with an ordinary torque converter clutch coupling.

 

Lock-Up Operation

The Transmission Control Module (TCM) sends output signal to the lock-up duty solenoid. Since the lock-up duty solenoid operates in proportion to the duty ratio, the amount of ATF drained from there is increased, thus lock-up duty pressure being reduced.

As a result, the lock-up control valve moves downward, which connects the torque converter regulator valve and the lock-up control valve apply port to each other.

In this condition, the oil pressure from the torque converter valve flows through the lock-up control valve apply port to the torque converter and the torque converter clutch. This causes a pressure differential across the lock-up piston. The piston is then forced against the impeller cover and turned as an integral unit with the cover. Thus, power from the engine is directly transmitted to the transmission input shaft. That is, the transmission is directly coupled to the engine.

 

The TCM controls the lock-up duty solenoid and the operation of the lock-up control valve. The force applied to the lock-up clutch is controlled for smooth clutch operation because the lock-up operating pressure is controlled by the lock-up control valve.

When locking up, the clutch is set in the half-engaged state beforehand. After this, the lock-up operating pressure is gradually increased to achieve smooth locking up.

 

E: LINE-PRESSURE CONTROL

 

The oil pump delivery pressure (line pressure) is regulated to the constant pilot pressure by the pilot valve.

The pilot pressure applied to the pressure modifier valve is regulated by the line pressure controlling line pressure duty solenoid and changed into the pressure modifier pressure.

The pressure modifier valve is an aux valve for the pressure regulator valve, and it creates a signal pressure (pressure modifier pressure) for regulating the line pressure to an optimum pressure corresponding to the driving conditions.

This pressure modifier pressure is applied to the pressure regulator valve to control the oil pump delivery pressure.

The pressure modifier pressure regulated by the pressure modifier valve is smoothed by the pressure modifier accumulator and pulsation in the line pressure is eliminated.

F: LINE-PRESSURE SHIFTING CONTROL

Function

Oil pressure which engages shift clutches (to provide 1st through 4th speeds) is electronically controlled to meet varying operating conditions.

In other words, line pressure decreases to match the selected shift position, minimizing shift shock.

 

Electronic Control Of Clutch Oil Pressure In Summary

Solenoids activate through the TCM which receives various control signals (throttle signal, etc.)

Control signals are converted into line pressure duty pressure, which is transmitted to the pressure modifier valve.

 

G: SHIFT PATTERN SELECT CONTROL

Shift pattern is selectable automatically between a base pattern suitable for ordinary economy running and a power pattern suitable for climbing uphill or rapid acceleration.

In the power pattern, the shift down point and shift up point are set higher than those of the base pattern. (sweet!)

 

Base Pattern To Power Pattern

Depending on throttle opening and vehicle speed, 16 areas as shown in the figure are set. Accelerator depression speed ds/dt for pattern change over is set for each area.

When the accelerator depression speed exceeds this set value, the pattern changes from base to power.

 

Power Pattern To Base Pattern

The power pattern is shifted to the base pattern, depending on car speed. Shifting to the base pattern is determined by the throttle position as shown in Figure below. Time lag in shifting is also determined by car speed. The maximum time lag is 3 seconds.

 

H: REVERSE INHIBIT CONTROL

This control prevents the transmission from shifting into reverse when the select lever is accidentally placed in 'R' range, protecting the components such as reverse clutch against damage.

If 'R' is selected during driving at a speed higher than the predetermined, the low clutch timing solenoid is energized.

Then, the pilot pressure is supplied to the reverse inhibit valve thus causing the reverse inhibit valve to move downward, thereby closing the low & reverse brake port.

In this condition, the low & reverse brake does not engage since the ATF flowing from the manual valve is blocked by the reverse inhibit valve.

As a result, the transmission is put into Neutral, and the shifting into reverse is inhibited.

 

I: GRADE CONTROL

While a vehicle is driving up a hill, gear position is fixed to 3rd gear for avoiding busy up and down shift between 3rd-4th gears.

When a vehicle is descending a steep hill under the designated vehicle speed (approximately 50 miles/hour), 4th gear downshifts to 3rd gear automatically by depressing the brake pedal. This gearshift control is released by re-accelerating with depressing the accelerator pedal. These controls are doing this based on the combination of throttle opening angle, engine speed, VS and so on.

 

J: LEARNING CONTROL

This transmission is provided with a learning control function which allows the transmission hydraulic pressure to be so controlled that the transmission makes a shift at the optimum shifting point according to the vehicle conditions.

For this reason, there may be cases where shift shocks become larger after the power supply is once interrupted (disconnection of battery terminal, flat battery, etc.) or immediately after the ATF is replaced.

Once power supply is interrupted, the hydraulic pressure correction values so far learned and stored are erased and the system is initialized (reset to the new vehicle conditions).

The system starts the learning again as soon as the power supply is restored, and after driving for a while, the transmission becomes shiftable at the optimum shifting points.

Lager shift shocks immediately after ATF change are caused by the change in friction characteristics of the transmission internal parts.

Also in this case, therefore, the transmission shifts at the optimum shifting points after driving for a while.

 

K: AWD TRANSFER CLUTCH CONTROL

 

L: TRANSFER CONTROL

The transfer hydraulic pressure control module is fitted with the transfer valve body attached to the rear end face of the transmission case via separate plate.

The hydraulic oil of the transfer hydraulic pressure control module is led from the oil pump delivery pressure circuit on the transmission case front to the transmission case rear. From there it is further fed to the hydraulic circuit of the transfer valve body.

The hydraulic oil pressure (line pressure) is regulated by the transfer duty solenoid and transfer control valve for obtaining optimum rear torque distribution corresponding to the driving conditions.

 

The pilot pressure is regulated to the transfer duty pressure by the transfer duty solenoid whose duty ratio is controlled by the TCM corresponding to the driving condition. (The transfer duty pressure varies with the degree of duty control.)

The transfer duty pressure is applied to the transfer control valve.

The line pressure is led also to the transfer control valve where the pressure is regulated to the transfer clutch pressure by the transfer duty pressure. (The transfer clutch pressure varies with the transfer duty pressure.)

The transfer clutch pressure is applied to the transfer clutch and causes the clutch to be engaged. In this way, the transfer clutch pressure is varied so that optimum rear torque distribution can be realized which corresponds to the vehicle driving conditions.

[JimFierst]

Thanks for the post.Way too complicated for me.. . I am trying to identify the source or cause of a transmission shudder/vibration problem.2000 Legacy OB,112K miles The idle is set at about 6 to 700 RPM and is smooth. When the trans is placed into gear or comes to a stop in gear the vehicle wants to move forward and must be held with the brake,. After a few seconds the trans begins to shudder . It seems like what ever senses engine rpm and feeds the TCU data is sending bad data or the trans is responding incorrectly.

Can a dealer run a set of diagnostic tests on the TCU??

[nipper]

Thanks for the post.Way too complicated for me.. . I am trying to identify the source or cause of a transmission shudder/vibration problem.2000 Legacy OB,112K miles The idle is set at about 6 to 700 RPM and is smooth. When the trans is placed into gear or comes to a stop in gear the vehicle wants to move forward and must be held with the brake,. After a few seconds the trans begins to shudder . It seems like what ever senses engine rpm and feeds the TCU data is sending bad data or the trans is responding incorrectly.

Can a dealer run a set of diagnostic tests on the TCU??

 

 

why not blame the axles, tires or wheels as well?

If you look over the threads, its the engine that does this, not the transmission. When in drive with your foot on the brake, you are oputting a load on the engine at its most inneffecient operating range. The engine is spinning the toque converter and front pump. The second half of the TC does not want to spin since you have your foot on the brake. There are actually LESS things moving in the transmission in this mode then in park or neutral.

In the engine it can be a dirty throtle plate, vacume leak, egr, IAC, plugs or wires, i can go on.

 

Now is the shudder even or does it a rythym to it. If it is even it is something that is common to all cylinders, if it is rythmic it can be traced to an indvidual cylinder.

 

 

nipper

[JimFierst]

The idle is normally very smooth . I just cleaned thew throttle body and valve .Plugs about 12K ago. It only happens when the car is stopped and the brake is depressed It tends to be even. I don't see how it could be tires brakes or axles..

Again and for one last time I will ask the question, Can a dealer run some sort of diagnostic program on the TCU.

[2X2KOB]

The dealer can run diagnostics on the TCU with the Select Monitor. However, I don't think you have a TCU problem. Both of our 2000 OBW's do this to some degree. I think it's more related to the gradual weakening of the motor and transmission mounts and the gradual loosening of interior parts which vibrate and make noise. I would almost call it normal for this car. Annoying, but normal. Or not uncommon - how about that.

[JimFierst]

Thank you very much...I did have the motor mounts looked at last week when I had the half shafts and O2 sensors replaced. It was not a dealer so perhaps he did not know what to look for.

I have an appointment with a dealer in CA this coming week and will request both of those be checked.

[porcupine73]

I had the half shafts ... replaced.

Yours would not be the first post describing this vibration when stopped in drive or reverse immediately after having the half shafts replaced with aftermarket rebuilt units.

[2X2KOB]

Yours would not be the first post describing this vibration when stopped in drive or reverse immediately after having the half shafts replaced with aftermarket rebuilt units.

 

This not being the first time I have heard this, and completely believing it, I still must ask: WHY?

[nipper]

This not being the first time I have heard this, and completely believing it, I still must ask: WHY?

 

 

The only thing i can think of is that the new half shfts may have some more mass in them (why dont people just get enitre axles?) . The new weight may magnify the normal NVH that the driveline produces. It is also possible that if one side was replaced, and the other wasnt, that the engine now is off balance, creating that vibration (i really like that theory).

 

Now if anyone out there has an afternoon to kill and is relly curious, somone can first try removing the cotter pins and see if the vibratio changes, or remove the shafts from the transmission and see if it goes away. Also it may require a really good scale (that can weigh ounces) and see if one half shaft is heavier then the other.

 

nipper

[2X2KOB]

But they aren't turning when the car is not moving. No movement, no vibration. I doubt that the axles play any significant part in the physical restraint of the engine/trans assembly, all these loads are taken by the motor and trans mounts. The previous explanation doesn't really make any sense to me, although I'm not going to worry about it too much.

[nipper]

But they aren't turning when the car is not moving. No movement, no vibration. I doubt that the axles play any significant part in the physical restraint of the engine/trans assembly, all these loads are taken by the motor and trans mounts. The previous explanation doesn't really make any sense to me, although I'm not going to worry about it too much.

 

Not true. The engine is rotating, the pistons are moving, the accesories are moving. There is a very busy chunk of metal under the car, even without forward movement.

 

Its added mass to the engine. the engine is vibrating. If you have mis matched weight on the engine, you can induce movement about the axis (yaw). If its not evenly done you can amplifier any vibration.

 

NVH is an amazing science.

 

nipper

[Aspen]

I think what he is saying is that the half-shafts are not moving when the car is stopped so this vibration issue is unrelated to half-shafts.

This is a perplexing problem. I think you need to experience it to get a better understanding.

My car is totally smooth at idle in neutral, park or underway, but vibrates when in gear at a stop. It's enough to make cd's in the door pockets and seat belts buzz. It's worse when the car is cold in the morning. Turn on the AC actually makes it better, sometimes.

It could be engine mounts, but I doubt it. I have changed everything else but the torque converter and TCU. It doesn't appear to be 02 sensors as the OP changed those. One assumes that the idle would be poor at all times if the cause was due to dirt or faulty plugs and wires.

I think I will swap the engine mounts in the summer just to eliminate the possibility.

 

Not true. The engine is rotating, the pistons are moving, the accesories are moving. There is a very busy chunk of metal under the car, even without forward movement.

 

Its added mass to the engine. the engine is vibrating. If you have mis matched weight on the engine, you can induce movement about the axis (yaw). If its not evenly done you can amplifier any vibration.

 

NVH is an amazing science.

 

nipper

[nipper]

I think it is related to the mass og the replacement half shafts. Forget anything about the car moving. When the car is in neutral or park the engine is not fighting a mechanical brake (the transmission). Everything is spinning freely. When the car is in drive, and not moving, the engine is under load. Engines under load run a little rough compared to no load. NOw add unequal weight on either side of the engine/tranny, you can magnify this vibration.

 

There is an entire specialty for this, its called NVH noise nibration and harshness. It's a bit complicated to explain over the net. Sometimes having mismatched weights on either side can make things far worse then one would think. You can induce vibration that was invisable before. It's part engineering part black magic.

 

You have a moment arm at the half shafts. For every distance X you move away from the center of the drive line, the affect increases. SO if one half shaft is heavier then the other, you can induce a rather heavy vibration.

 

nipper

[Tech1967]

Forgive me if I seem rude but Nipper are you teasing him?

[nipper]

Forgive me if I seem rude but Nipper are you teasing him?

 

NO!

 

after seeing many of these posts, this is the best explanation i can come up with.

 

 

I dont understand what the problem is. NVH is a engineering specalty all on its own.

 

IF you have a long peice of steel (steel rule comes to mind) thats fleaxable, move your hand up and down holding it in the center. It will move equally and smoothly. Now Start adding weight to one side and slowly move it out (even a penny will do). You will see that it doesnt have to move out very far from where your holding it to see a major difference.

 

This is the best example i can think of off hand right now. Mass of equal weight can dampen oscilations and vibrations, unequal weights can cause unpleasant vibrations, and can shake things loose

 

Its simple physics to describe it and shoe it, complicated to solve sometimes.

 

Next time somone changes a half shaft, amuse me and weigh it.

 

nipper

 

Anyone else have a better theory?

[Tech1967]

How about the halfshafts as torsion bars upon which the "weight" of the engines power rests. Maybe take in all the posible areas of play in this setup. Play in brakes, tires, joints, mounts. Maybe look at the torque converter, and the effect of misfire. Yes there is a certain percentage of misfire in all engines no matter what state of tune they are in. Yes component weight could play a part in this, maybe a change in harmonics or something. I have some trouble believing that a couple grams difference in all of this could be the sole cause though it may accentuate an existing condition.

[nipper]

How about the halfshafts as torsion bars upon which the "weight" of the engines power rests. Maybe take in all the posible areas of play in this setup. Play in brakes, tires, joints, mounts. Maybe look at the torque converter, and the effect of misfire. Yes there is a certain percentage of misfire in all engines no matter what state of tune they are in. Yes component weight could play a part in this, maybe a change in harmonics or something. I have some trouble believing that a couple grams difference in all of this could be the sole cause though it may accentuate an existing condition.

 

But the question is, is it a couple of grams ? Thats what we need to findout. So anyone work in an store that sells half shafts?

 

And in harmonics it really doesnt take much.

 

nipper

[Tech1967]

Well then if it happens right after the axles are done and the weight/construction is the difference then it's a matter of bucking up for the Soob parts to eliminate an annoyance. It would seem that it's not a real mechanical problem unless it has the potential to do damage over time.

[Aspen]

Just to get back on topic.

 

The halfshafts in my wagon are the originals and in good condition. So that is not the source for me. I think it is one of:

1) torque converter

2) TCU

3) engine mounts

[nipper]

Just to get back on topic.

 

The halfshafts in my wagon are the originals and in good condition. So that is not the source for me. I think it is one of:

1) torque converter

2) TCU

3) engine mounts

 

TCU doesnt really do anything when the car isnt moving (in gear or not).

Torque converter always there.

Engine mounts/tranny mount possible.

If you really want to get insedious there is this big rotating mass behind the torque converter that is succeptable to wear, its called the front pump in the transmission.

Possible cracked flex plate

I still say its engine related if the half shafts havent been changed. Need to find a shop with a Sun engine analyzer to see what they can find. The ECU is a horrible dignostics tool for this kind of thing.

 

nipper