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I have an auto 95 that I bought this summer which is is not upshifting to 4th when cold and when accelerating to 60+ on the expressway. During the summer, it upshifted fine at 3500 rpm and it will upshift after driving it awhile. I checked the search function and not much help. I drained/changed atf twice after I bought it so it's in pretty good condition. Car has 208K miles.

 

Not that it probably help, but what causes it to upshift. One person says its the throttle position sensor and another says a temperature probe?

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Once warmed up it shifts fine?

 

If so the TCU is programmed to stay in 3 until the engine is at a certain temperature for pollution reasons, so it could be "normal".

 

I had a 95 Legacy and altered my route to work in the winter because I was less than 3 minutes to a major 65 mph highway and I'd have to endure driving another 4 or 5 minutes at high RPMs just to keep up with the slow traffic.

Edited by Suzam
Changed "ECU" to "TCU"

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I've taken a peek at the software inside the TCU on my '92.

 

The TCU will not shift to 4th gear until the trans temp reaches 64 F. It will lock up the torque converter at 162 F. The temperature lamp comes on at 230 F.

 

I added a cooler on mine, and it would take longer to lock up the torque converter. So I modified the software and lowered the lockup temp just a bit. :D

Edited by presslab

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Thanks, that explains a lot. I didn't even know that there was a transmission control unit. If TCU needs a temperature above X to upshift to 4th gear, then its explained although I have never noticed a problem with my other 6 subarus.

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i call bull i test drive them stone cold and shifts 1234 lockup even ice cold a delayed shift is caused by to mutch clearance in the forward clutch pack drum. Have never heard of it having to be a certan temp to work it makes no sense what whould be the purpose of waiting for it to be warm to shift ? what if you pull out strait onto freeway ice cold and need to hit speed having to wait to warmup to shift whould be unaxceptabble and dangerus.I cant belive subaru whould do thiss. I think there is more to your problem

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It's certainly in the code in my 1992 TCU. Perhaps later TCUs did away with this, I don't know. I can show you the code tonight when I get home.

 

In 3rd gear you can go any reasonable speed, I don't see how it's dangerous. If I recall I can do about 120 MPH in 3rd. Heck my trans will pull 2nd all the way to 80 MPH. Running the engine faster warms it up sooner reducing emissions and wear.

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MY 95 was ALWAYS reluctant to shift up to 4th when the temperature dropped below 30° F in winter. I bough the car brand new and it always did it. The action was confirmed by a master mechanic in 1996 as a way to reduce cold engine emissions. I can't recall if it's only the 2.2 or not but could be it dosen't effect the 2.5.

 

There are older threads on the board discussing this delay of shift to 4th when cold.

 

I've also had a 97 & 99 2.2 that did not do this, or if they did, not to the same extreme as the 95 2.2 did maybe soa adjusted the specs later on.

Edited by Suzam
Added info and can't spell.

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as far as i know the temp senser in the trans is for default if overheated not to tell tcu what temp the trans is. If the trans overheats to the point of turning on the AT light the fans will turn on to try and cool it. I have many auto outbacks that come thrugh so will test drive them all cold and see if there is a difference in how they shift hot /cold

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as far as i know the temp senser in the trans is for default if overheated not to tell tcu what temp the trans is. If the trans overheats to the point of turning on the AT light the fans will turn on to try and cool it. I have many auto outbacks that come thrugh so will test drive them all cold and see if there is a difference in how they shift hot /cold

 

I'd be interested in your results. Especially relating to a 95 model.

 

I'm pretty sure you get enough cold weather where you are in BC. :grin:

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Here's the code in question. Basically if the trans temp is below "ATF_TempCold" it will set bit 6 in shiftFlags1. If bit 6 (or 7) is set in shiftFlags1 and the calculated gear is 4th, it will reduce the gear to 3rd. It does a bunch of other things with trans temp like it has a temperature compensation for the Duty A (line pressure) solenoid, so that it will lower the duty cycle because the fluid is cold and thick. It looks at all sorts of inputs, even the battery voltage, to determine the operation of the solenoids.

 

 

seg006:D683		    cmpa    ATF_TempColdseg006:D686		    bhi	    loc_D68Aseg006:D688		    orab    #$20 ; ' 'seg006:D68Aseg006:D68A loc_D68A:				    ; CODE XREF: GetADC+63jseg006:D68A		    stab    shiftFlags1

 

and...

seg006:D8F2		    ldaa    shiftFlags1seg006:D8F4		    anda    #$60 ; '`'seg006:D8F6		    beq	    loc_D901seg006:D8F8		    ldaa    byte_BCseg006:D8FA		    cmpa    #3seg006:D8FC		    bne	    loc_D901seg006:D8FE		    dec	    byte_BCseg006:D901seg006:D901 loc_D901:				    ; CODE XREF: CalcShift+8j

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