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EcoCivic 03-07-2019 01:05 PM

Manual TCC control
I have been experimenting with manually controlling the torque converter clutch lockup on my 2005 Honda Civic to improve fuel efficiency and performance. o far so good. HOWEVER, I am not completely sure what effects these mods can have on the short term or long term reliability and longevity of the transmission. I do not think that I am doing harm, but I am far from a transmission expert and I may be causing damage, so please proceed with caution if you choose to do something similar. Also, keep in mind that my PCM is not stock. It is from a JDM Honda Stream, so I am not sure how a USDM PCM would react to these mods.

The first thing I did is I unplugged the connector from the TCC control solenoid, plugged in an extra solenoid with the same connector so it didnít set a code and go into limp mode, and just wire a switch to activate the solenoid. The switch did work. However, it didnít provide complete control over the TCC lockup. For example, it would not lock in first gear, it would not kill the engine if engaged while idling in gear, and it would not engage the TCC clutch if the trans was manually locked in second gear. Also, if I pressed the gas more than a little bit with the converter locked, the PCM would somehow unlock the converter partiallly, which really confused me at first.

What I ended up doing is bypassing the clutch pressure control solenoids by unplugging them and plugging in extra solenoids to keep the oil pressure high constantly and wow what a difference that made! The trans now shifts MUCH quicker and firmer, which I prefer. IMO it is not harsh at all as long as it isnít shifting with the TCC locked.

But more importantly, I now have full control over the TCC lockup. I can force a lockup at will, regardless of speed or what the PCM wants. IMO that is pretty cool for a couple of reasons. One is obviously the potential for better gas mileage, and another is something some people may not expect- In low gears at full throttle, the car actually seems to respond much quicker and accelerate better since the torque converter canít waste power that can be going to the wheels.

However, one problem with manually controlling the TCC is that it throws off the PCMís shifting strategy. For example, if I am climbing a hill in 3rd gear and the trans up shifts to 4th gear, the speed might be too low for the TCC to be engaged in high gear under load. I bet that if I could shift to D3 to keep the trans from upshifting to 3rd gear this would not be a problem. However, I havenít been able to get D3 to work yet with this PCM, basically because the Honda Stream that this ECU came out of doesnít use the TRS to activate D3, instead it uses a switch by the shifter.

So I think that I might install some type of 4 position rotary switch to manually shift the gears. I have already determined which solenoids are activated in which gear by running the car in gear with the wheels off the ground and checking which solenoids get power in each gear. Basically, one solenoid is activated for first gear, both solenoids for second gear, the other solenoid is activated for third gear, an both solenoids are off for 4th gear.

Anyways, any thoughts, suggestions, questions, or comments are welcome as always

me and my metro 03-07-2019 11:25 PM

If you are the only driver you could make a switch panel and drive it like a stick shift. Maybe even add a shifter for a manual and have it switch the gears. Nobody would be able to steal it!

Piotrsko 03-08-2019 10:48 AM

So default condition is lock up in 4 th gear with no power applied to the solenoids ?

EcoCivic 03-08-2019 11:06 AM


Originally Posted by Piotrsko (Post 593079)
So default condition is lock up in 4 th gear with no power applied to the solenoids ?

Great question! I should have been more clear about the default lockup and shifting function. Default operation with no power applied to any solenoids is torque converter unlocked and trans in 4th gear. To lock the torque converter, power must be applied to the lockup solenoid.

Also, if any solenoid is simply unplugged, the PCM goes into limp mode and keeps the trans in 4th gear unless the shifter is put in 2. Does that make sense?

Piotrsko 03-08-2019 12:53 PM

Yup. Rotating switch of some sort and you can have paddle shifting. Oops you already know that.

EcoCivic 06-17-2019 04:46 PM

I have an update. Unfortunately my transmission completely died. It started slipping badly when it shifted, and the next day it completely died and the car had to be towed home. I am not sure if it just died because it has 243K miles on it, or if it died because of the manual TCC control. But either way, it's getting a "new" JDM SLXA transmission from a Honda Stream. There isn't much information available on the gear ratios of an SLXA transmission, but I remember reading that the final drive is a little higher because it is from a heavier vehicle. The US BMXA transmission has a final drive ratio of 4.067:1 and I found on Honda Japan's site that the SLXA Stream transmission has a final drive of 4.357:1 and slightly more aggressive gearing, so that's nice since performance is my main goal.

hayden55 06-17-2019 05:22 PM

If you're feeling frisky and down on your luck. Make sure you have full coverage. Park it in North Memphis with the keys in it and I promise it will be gone in 24 hours!
Next go around I would get a s2000 if performance is your main goal. I like those. ;)

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