power mode still/again

spinn360 · #1 04-09-2006, 11:59 AM

So the car keeps going into power mode. Not just the power light coming on. but the actuall shift points changing to about 5 grand. I thought the tps was the culprit and it was replaced with a used one. took a while to set it as the butterfly valve wasnt closing all the way. ( I had to clean it

) Then got it set to .5v. Car ran good for about 1 week. then power mode started coming on. More frequently now. I am thinking it is the TCU. I paid for one, and its supposed to be on the way soon(I hope). the power mode came on yesterday when I was stopped at a stop light, at a freaking stop light! No gas applied, no change in throttle position!

I can turn it off when I am on the highway by turning the cruise control on, but when I do that, the tranny goes to 3rd gear even at 70 mph. When I am in town I can stop the power mode from coming on by pushing the manual button and shifting from 1st to 2nd gears manually. I am not sure but I thought I would post this to see if anyone else has had this prob. Or if anyone knows how to fix this. I am set at a very tight budget right now and I cant afford anything over 100 dollars so, I cant replace the TPS with a new one(besides the fact that I dont believe this would do anything). Someday maybe I will put the 5mt in but that will have to be further down the road. God I hate Automatics.

Please if anyone can help that would be great.

intelisevil · #2 04-09-2006, 02:56 PM

I hope you get your problems sorted out. With all of the 5-speeds floating around, there have to be a lot cheap TCUs available.

With all of the SVXs out here in Oregon, I really wish we had a TomsSVX in the neighborhood!

Dan

b3lha · #3 04-09-2006, 04:28 PM

Measure the voltage of the white wire at pin b8 of the TCU. This is the wire from the TPS to the TCU. With the throttle fully closed it should be 4.0 to 4.8 volts. At WOT, it should be somewhere between 0.7 and 1.7 volts. Go for a drive with the voltmeter connected and see what the voltage is when your spurious power mode occurs.

If power mode activates while the voltage is >1.7 volts then the TCU is at fault, otherwise the TCU is just doing what it is told.

oab_au · #4 04-09-2006, 04:55 PM

Could be the ATF temperature sensor in the trans, that is reading wrong. It will put it in Power Mode, to cool the ATF.

Harvey.

Trevor · #5 04-09-2006, 07:45 PM

Quote:

Originally Posted by oab_au

Could be the ATF temperature sensor in the trans, that is reading wrong. It will put it in Power Mode, to cool the ATF.

Harvey.

Exactly which and what circutry will activate this feature, which I can not find refered to elsewhere. ?

Are you saying that this will raise the shift points at all degrees of throttle opening and will as a result, lower the transmission fluid temparature to a worthwhile degree ? If so, those with Power Mode switch could keep this mode in constant operation to advantage. It is strange that this idea has not been previously been brought up here.

Trevor.

SomethingElse · #6 04-09-2006, 08:45 PM

its probably some kinds of thermistor. resistance changes with tempreture..just like a coolant temp sensor. oh well no more automatic so i dont have to worry about it

Trevor · #7 04-09-2006, 10:33 PM

Quote:

Originally Posted by Kulaid

its probably some kinds of thermistor. resistance changes with tempreture..just like a coolant temp sensor. oh well no more automatic so i dont have to worry about it

I regret that you appear to have been led up the garden path on this one. Make no assumptions until there is a reply to my post.

spinn360 · #8 04-10-2006, 12:50 PM

I will try to check the votage when I get home. If I get the time thanks for the advice. Which one is B8? All I have for reference is the adobe pdf files, from member Lee, to show me. And the plugs it shows are (I think they're the female connection in the tcu) B66, B67, B68. Did you mean B68?

TomsSVX · #9 04-10-2006, 06:34 PM

Quote:

Originally Posted by oab_au

Could be the ATF temperature sensor in the trans, that is reading wrong. It will put it in Power Mode, to cool the ATF.

Harvey.

My understanding was that the temp sensor was to serve 2 functions. Allowing the trans to stay out of 4th gear until the temo reached 50*F and then keepin the TC from locking until it reach 150*F(I think). Maybe this is what you were thinking? I have never heard of the temp sensor having anything to do with the power mode. Infact you can still engage power mode when it is freezing cold or fully warm.

Tom

SomethingElse · #10 04-10-2006, 08:12 PM

I dont have a garden path

Earthworm · #11 04-11-2006, 10:23 AM

Power mode will not cool the ATF...locking the torque converter will.

TomsSVX · #12 04-11-2006, 10:57 AM

actually, it won't. See the cooling effect comes when the fluid is moving fast enough that it will hit the cooler that much sooner, so spinning the oil pump faster is the main objective. Thus why I would say the TC wouldn't lock in that case

Tom

Earthworm · #13 04-11-2006, 11:38 AM

Those who have had a temperature gauge for their tranny will know that when the torque converter is locked the tranny actually cools off. Power mode means max TC slipping meaning max heat.

The torque converter is a furnace for the ATF which is why MT's don't usually require external cooling.

SVX-FF · #14 04-11-2006, 12:51 PM

I found this in a "End Wrench" doc titled "Subaru 4EAT Transmission"

When the ATF is cold, the TCU won’t allow an upshift into 4th gear. The object is
to warm the engine quickly for lower emissions. It is more sophisticated than the
KDLH system and less objectionable for the consumer.
ATF Temperature Sensor
When the ATF is hot (AWD only), the TCU shifts the transmission as if in the
POWER mode. This pushes the shift points higher which allows the engine to run
faster. The oil pump then circulates ATF through the oil cooler more quickly so as
not to overheat the engine coolant.

BTW what is Trevor's problem, boy is he snappy

Steve

spinn360 · #15 04-11-2006, 05:52 PM

So does B8=B68? I dont have a FSM.

I also have an oilcooler installed infront of the ac condensr so the heat from the rad doesnt effect it as much. maybe the TC isnt locking because it hasnt warmed up enough. But it goes into 4th just comes out when I have cruise on. Its going into powermode when the car has only been running for like 1 min. So I dont think its over heating. Yeah maybe the heat sensor(if it does what you say). But would it show up with a code? And would it also make the fluid temp light come on? because niether of these is happening. I guess I will probably change the TCU before I find out which wire to test and if that fixes it (fingers crossed) then I wont care. But if it doesnt(knock on wood) then I will ask again, if no one answers right now that is.