Jump to content

Welcome to Ultimate Subaru Message Board, my lurker friend!

Welcome to Ultimate Subaru Message Board, an unparalleled Subaru community full of the greatest Subaru gurus and modders on the planet! We offer technical information and discussion about all things Subaru, the best and most popular all wheel drive vehicles ever created.

We offer all this information for free to everyone, even lurkers like you! All we ask in return is that you sign up and give back some of what you get out - without our awesome registered users none of this would be possible! Plus, you get way more great stuff as a member! Lurk to lose, participate to WIN*!
  • Say hello and join the conversation
  • Subscribe to topics and forums to get automatic updates
  • Get your own profile and make new friends
  • Classifieds with all sorts of Subaru goodies
  • Photo hosting in our gallery
  • Meet other cool people with cool cars
Seriously, what are you waiting for? Make your life more fulfilling and join today! You and your Subaru won't regret it, we guarantee** it.

* The joy of participation and being generally awesome constitutes winning
** Not an actual guarantee, but seriously, you probably won't regret it!

Serving the Subaru Community since May 18th, 1998!

Guest Message by DevFuse

* * * * * 1 votes

"Power mode" for 95-99 4EAT TCU's

  • Please log in to reply
13 replies to this topic

#1 WoodsWagon


    Formerly 91Loyale

  • Members
  • 4,102 posts
  • NH

Posted 02 November 2010 - 08:22 PM

As you may or may not be aware, early 90's SVX's came with a power mode button in Japan. US models didn't get it, probably for EPA fuel milage reasons. But the pin on the Transmission Control Unit was still there and the programming code still existed in the US TCU's. So it's popular in the 91-94 legacys to move the female pin on the 20 pin connector from postion 6 to position 4. This then makes the "manual" button on the shifter turn on the "power mode".

Power mode is the equivalent of a sport shift button on a newer car. The TCU uses a different shift map so that it holds gears longer, downshifts sooner, and won't lock the torque converter clutch. It makes the transmission much more responsive and fun to drive. There is a small gas milage penalty, around town it's only a MPG or 2, but on the highway it is more because of the torque converter not locking up.

So in 95 subaru switched to OBD-II. This required a complete redesign of the ECU (engine control unit), wiring harness, and TCU. All the pins on the TCU that used to control the "power" and "manual" lights on the dash and the input for the manual mode button have been redesignated as communications lines for the OBDII systems. The TCU case and board have also been redesigned with the plugs on the side instead of the bottom. But through this all, pin 4 on the 20 pin connector was still left unused.

I pulled a pin and pigtail of wire from a 20 pin TCU connector on a spare harness and put it in postion 4, which is the only unpopulated pin on the latching tab side of the 20 pin connector, which is the higest connector up on the TCU. The TCU is to the left of the brake pedal above the drivers feet by the way, big gold box with 3 connectors. You have to release the locking bar on the back of the connector, push the pin in until it clicks, fold the locking bar back into postion and plug the connector back in.

Power mode is activated by grounding pin 4 on the early TCU's. I grounded pin 4 on the 97 OBDII TCU and while it can no longer light up an indicator of power mode being activated you can tell by driving. At part throttle at 45mph it was holding 3rd gear with the engine up around 3k rpms. Unground pin 4, it would shift to 4th and lock the TC dropping the RPMS down in the same driving conditions. It downshifts as soon as you roll into the throttle, rather than having to stab the throttle to WOT to getting it to downshift like you normally do. Much more responsive and fun to drive.

All you need for the mod is a small switch, some wire, and a TCU pin and pigtail. Set up the switch to ground pin 4 of the 20pin TCU connector to a chassis ground and you will have sport mode on command. This should work for a 95-98 TCU, outback or legacy. I'm not sure about the 99's as they changed some things with the bellhousing pattern and ABS sensors among other things and I don't have a 99 handy to test with. I'll try out a 98 outback tomorrow.

Here's a picture borrowed from "Nomake Wan" on subaru-svx.net
Posted Image

Edited by WoodsWagon, 03 November 2010 - 02:54 AM.

#2 idosubaru


    Elite Master of the Subaru

  • Members
  • 24,010 posts
  • East Coast

Posted 02 November 2010 - 08:52 PM

nice hit! it'll work on all EJ's within those years, impreza too.

#3 TheLoyale


    Safariwagon: The Legend

  • Members
  • 7,079 posts
  • Waukesha, WI

Posted 05 December 2010 - 07:55 PM

Oh wow, this is one great idea!

Thanks for posting it!


#4 SchwarzeEwigkt


    USMB is life!

  • Members
  • 148 posts
  • Rochester, NY

Posted 05 December 2010 - 08:07 PM

I plan to try this myself.

...after it stops snowing.

#5 eulogious


    Inspiring Subaneer

  • Members
  • 1,090 posts
  • Olympia, WA

Posted 07 December 2010 - 05:53 AM

It does still lock the TC up, just takes a while at cruising. It's does make the car feel sportier than stock for sure, and I really don't think it effect gas mileage that much.

When I use my paddle shifter code for my TCU it uses the power shift maps, and it's alot of fun driving around in power mode all day long. Even on the freeway it will lock up the TC and give you decent mileage. I have even heard of guys just keeping it on all the time and not really noticing to much of a difference in anything other than having more fun driving around.

Good stuff :)

Thanks for the write up on this!

#6 eulogious


    Inspiring Subaneer

  • Members
  • 1,090 posts
  • Olympia, WA

Posted 07 December 2010 - 07:57 AM

Here's the "geeky" break down of the power button, and what it actually does in the code. Kinda cool if you like that sort of thing like I do :grin:


#7 TheLoyale


    Safariwagon: The Legend

  • Members
  • 7,079 posts
  • Waukesha, WI

Posted 25 December 2010 - 03:37 PM

Where is the TCU box? I see a small aluminum box under the dash on the drivers side, its held up with two 10mm nuts. Is that it?

Its been to cold for me to really look, I just want to know cause its been bugging me :)

#8 CNY_Dave


    03 LL Bean H6

  • Members
  • 1,912 posts
  • Near Cortland NY

Posted 04 January 2011 - 08:46 AM

Similar tweak you could do to some other cars- on my '03 H6 OBW the trans is more prone to downshift/hold a lower gear when ther cruise is engaged- in this situtaion you could hook a button to the TCU pin that signals 'cruise engaged' and you'd have a sport-shift button.


#9 KZCool


    Advanced Member

  • Members
  • PipPipPip
  • 47 posts
  • North Vernon, IN

Posted 16 August 2014 - 06:17 PM

So this wouldn't work for a '99? Mine never wants to downshift unless I come to almost a complete stop and sometimes when I give it gas to pass.  Could be a different problem altogether though. 

#10 99 subie outback

99 subie outback


  • Members
  • PipPip
  • 10 posts
  • Medina/North Canton, Ohio

Posted 20 February 2015 - 02:03 PM

I really wanna try this on my 99.

#11 99 subie outback

99 subie outback


  • Members
  • PipPip
  • 10 posts
  • Medina/North Canton, Ohio

Posted 14 March 2015 - 06:54 PM

Well I got to workin on it today. And I'm not so sure now. I am scratchin my head. My TCU(trans control unit) or TCM(trans control module) whatever you wanna call it. Aren't they the same. I don't have a 20 pin connector, I have 2 that are 24 and only have 23 wires in them. Took some pics. I did find the ECU and it is a 20 pin connector, but I'm not messin with it.












Edited by 99 subie outback, 14 March 2015 - 06:54 PM.

#12 wtdash


    Subaru Nut

  • Members
  • 1,591 posts
  • N. ID

Posted 19 June 2015 - 02:50 PM

Borrowed pic from above post:


On the attached pic see arrow to where extra wire needs inserted to 'ground' pin and turn on Power Mode. 


Here's a LINK to this as well.


To Enable Power Mode for '99+:

.... On the phase 2 transmission, it's pin 20 on the white plug.......pin 20 is between the blue/white and the white/red wires on the white connector.


Attached Files

#13 ccrinc


    The Subaru Whisperer

  • Members
  • 1,034 posts
  • Denver, CO

Posted 19 June 2015 - 03:29 PM

I've mentioned a shift kit on this forum many times before that's added to the valve body.  It does the same thing. 

The BEST side effect of this is that it makes the transmission less easily damaged by the high torque from an SVX engine, Legacy turbo engine, etc.  In fact, that's the big advantage: it takes that torque and applies it for more power and response.  I'm not sure it will do much for a low torque engine, in fact. 


But, hey.  It's worth a try, right?!





    Elite Master of the Subaru

  • Members
  • 3,963 posts
  • Tazewell Virginia

Posted 19 June 2015 - 09:20 PM

This thread should be titled power mode for 95-98 tcus, all 99+ tcus are phase 2 and the wiring change is different from phase 1s. I have seen the power mode mod for phase 2 tcus online, just search for it.

0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users