Torque Converter Lock-Up Switch Mod for A340 / A3040LE (and similar Aisin autos)

[Alex From KZ]

This transmissions have been widely used on many vehicles, in my case this has been done on two of my cars 1994 Hilux Surf with 1KZte and Prado 78 with 2LTE engines.

This is simple, cheap but very effective mod for anyone running an Aisin A340, A3040LE, or similar Toyota autos (Prado, Hilux, Surf, LC, etc.)

What it does:

Adds a switch that lets you manually command torque converter lock-up instead of relying 100% on the ECU logic.

Why it’s useful:

Lower transmission temps (big one for towing)

Eliminates converter slip on long climbs

Better engine braking downhill

More direct feel on highway cruising

Less heat = longer ATF life

Less heat and strain on long hills for engine (big for old toyota engines)

How it works (basic):

Lock-up solenoid is normally ECU-controlled

On Hilux surf with 1KZ it will lock up at 80kph, on my prado at 70kph, if you drive under this speed it stays unlocked, which sucks at long hills.

Switch supplies 12V to force lock-up

CAN Be used in 2nd 3rd or 4th gear, 1st gear will not lock up converter in these transmissions.

For this mod you will need:

2 5pin relays

Momentary switch (not lockable)

1 diode to prevent 12v going to your ecu

A few meters of wire

Bellow I will include wiring diagram for different vehicles. And scheme on how to make it work.

How does it work:

- You press bottom and it sends 12V to relay 1

- Relay 1 closes and sends 12V to solenoid SL in transmission

- Torque converter is locked at this point

- when you press brake pedal

- 12v from brake switch is sent to relay 2

- it Unlocks relay 2

- Relay 2 brakes ground wire on relay 1

- torque converter unlocked

Pay attention to Relay 1, pins 85 and 87 have to be connected, this will allow relay to sway on when you press on momentarily switch. To unlock it, you brake ground point (pin 86) by using relay 2.

Who benefits most:

Diesels (2L-TE, 1KZ-TE, 1HD, etc.)

Towing / overlanding setups

Lifted rigs with big tires

Hot climates or mountain driving

I’ve been running this setup for a while and the temp drop alone made it worth it. Simple mod, big payoff.

Happy to answer wiring or usage questions if anyone’s interested.

 

[simonliew]

Good job
Going to try it on my surf and Prado.

 

[AVL KZJ78]

Interesting, I will try it. To clarify- a press of the momentary switch energizes the lockup solenoid, and a press of the brake pedal unlocks it? What about using an on/off switch instead of momentary to allow for engine braking and service braking at the same time?

 

[Alex From KZ]

Interesting, I will try it. To clarify- a press of the momentary switch energizes the lockup solenoid, and a press of the brake pedal unlocks it? What about using an on/off switch instead of momentary to allow for engine braking and service braking at the same time?

You can do it too, it would be even easyer, but during city driving you may experience stalling, because when you pull up to the traffic light, your transmission stays in 4th gear almost untill full stop, so if you leave lock up on, you engine will stall. The scheme which I described, works almostst like factory and it will stay on, unless you press brake pedal. I find it working the best for my needs,.

 

[Alex From KZ]

Interesting, I will try it. To clarify- a press of the momentary switch energizes the lockup solenoid, and a press of the brake pedal unlocks it? What about using an on/off switch instead of momentary to allow for engine braking and service braking at the same time?

You can just cut the wire and apply 12v to the solenoid using regular “stay on” switch, drive around and feel for yourself how your car behaves and then decide. All you need as a switch, peace of wire and a little bit of time

 

[AirheadNut]

Very neat modification! I know the A343f used in the LJ7x Prados uses lockup in 3rd and 4th gear, can this system be used in 1st and 2nd as well? That would be particularly useful when climbing long hills at low speeds.

 

[Ash Awbery]

I have manualised my A343 in my LJ78 (with 1KZ) and also have the TC lock up on a switch, makes a big difference to the drive ability, my TC lock up worked in all gears so I have wired it to only work in 3rd and OD.

 

[Alex From KZ]

Very neat modification! I know the A343f used in the LJ7x Prados uses lockup in 3rd and 4th gear, can this system be used in 1st and 2nd as well? That would be particularly useful when climbing long hills at low speeds.

2nd gear - yes. I 1st no.

 

[sheeeep]

Thank you for the write up, I have done a similar mod in the past on my Surf, but haven't done it to my prado as I don't like the stalling if you forget to switch it off, and this setup eliminates that. I have ordered an OE looking momentary switch for my 90, and will build a small box to house the relays etc under the center console.

I have a couple of questions on the relays. Looking at what I can get in NZ, i have access to fused or no fused relays with Diode or Resistor protection on the 85 and 86 pins, does it matter which protection I use and would you use a fused relay or rely on the factory fusing from the ignition?

 

[Alex From KZ]

Thank you for the write up, I have done a similar mod in the past on my Surf, but haven't done it to my prado as I don't like the stalling if you forget to switch it off, and this setup eliminates that. I have ordered an OE looking momentary switch for my 90, and will build a small box to house the relays etc under the center console.

I have a couple of questions on the relays. Looking at what I can get in NZ, i have access to fused or no fused relays with Diode or Resistor protection on the 85 and 86 pins, does it matter which protection I use and would you use a fused relay or rely on the factory fusing from the ignition?

You can use one with protection. It would not hurt anything. I used the one without protection, just because I had it laying around. Works both ways just fine

 

[sheeeep]

You can use one with protection. It would not hurt anything. I used the one without protection, just because I had it laying around. Works both ways just fine

Thanks! I have built mine into a small box, with a deutch connector so i can remove it easily if needed. Only other question I have, is around the Diode. based on the diagram, I cut the wire to the solonoid and put the diode in, then connect the wire from the relay to the solonoid wire and reconnect it to the diode for protection. Presumably thats so if the system off the ECU controls lock up like factory. What amp capacity Diode do you think is needed? I have a 6a diode with a surge capacity of 10 amp, or could I go smaller? from what I can see a tcc solonoid can pull abut 3 amp max so i assume 6amp is fine.

 

[Alex From KZ]

Thanks! I have built mine into a small box, with a deutch connector so i can remove it easily if needed. Only other question I have, is around the Diode. based on the diagram, I cut the wire to the solonoid and put the diode in, then connect the wire from the relay to the solonoid wire and reconnect it to the diode for protection. Presumably thats so if the system off the ECU controls lock up like factory. What amp capacity Diode do you think is needed? I have a 6a diode with a surge capacity of 10 amp, or could I go smaller? from what I can see a tcc solonoid can pull abut 3 amp max so i assume 6amp is fine.

You can use 6 apm, and be fine. The reason diode is there in the first place is to protect your ECU, so when you apply 12v it only goes to solenoid and not to ECU and fry something. Diode works only one way.

- cut wire going from ECU to solenoid
- place diode in correct orientation, so your ecu car send 12v when it wants to the solenoid
- then you place wire from your manual lock up AFTER diode, now when you apply 12v your self it only goes to solenoid and diode prevents it from going back to ECU. And at the same time when your ECU sends 12v to solenoid it can do it too

 

[sheeeep]

Me again, sorry, im not much of an electrical guy so im struggling a little
I have built my harness and box, and am ready for the last two terminations, my two questions
Based on your diagram above for the ECU pinout, on the KZJ95 SL would be the solenoid lock up right? Pin C1. I ask as there is a lot of conflicting info on the ECU pinout, and yours it the only one that looks like my ECU with 3 plugs. SL is a pink wire on my truck which according to the internet is the TCC lockup solonoid.

Regarding the brake light switch, there are two wires, one has constant 12v, and the other I assume gets 12v when the brakes are activated, i assume its the wire without 12v constant I want to tap into?

My plan is to test the unit without looking it to the TCC solenoid to verify my wiring etc, so I just want to be 100% before I cut and splice.

 

[Alex From KZ]

Me again, sorry, im not much of an electrical guy so im struggling a little
I have built my harness and box, and am ready for the last two terminations, my two questions
Based on your diagram above for the ECU pinout, on the KZJ95 SL would be the solenoid lock up right? Pin C1. I ask as there is a lot of conflicting info on the ECU pinout, and yours it the only one that looks like my ECU with 3 plugs. SL is a pink wire on my truck which according to the internet is the TCC lockup solonoid.

Regarding the brake light switch, there are two wires, one has constant 12v, and the other I assume gets 12v when the brakes are activated, i assume its the wire without 12v constant I want to tap into?

My plan is to test the unit without looking it to the TCC solenoid to verify my wiring etc, so I just want to be 100% before I cut and splice.

Yes, correct, you dont want constant 12v from your brake pedal. You only want 12v when you press the pedal.

As far as diagrams, They should be correct, never had a chance to check for j90 platform, but for my KZN130 Surf all matched perfectly. So, i assume that it should be the one.

 

[sheeeep]

Massive thank you to Alex. The ECU pinout was correct, verified it by going for a drive with the multimeter pushed into the plug. System works great and is absolutely fool proof when in operation. Thanks again!

 

[Jern]

Good to hear! I think I’m going to give it a go too and have a good spot for the button. Would this also work with the A343 valve body upgrade from Transgo?

 

[sheeeep]

Good to hear! I think I’m going to give it a go too and have a good spot for the button. Would this also work with the A343 valve body upgrade from Transgo?

Cant help with the transgo kit, but regarding the switch, I bought my switch from Switchboss in Aussie, matches the stock prado switch, and works well. Looks like toyota put it there if youre searching for a switch, in my 90 it sits next to where the shifter is in an unused hole

 

[Jern]

Cant help with the transgo kit, but regarding the switch, I bought my switch from Switchboss in Aussie, matches the stock prado switch, and works well. Looks like toyota put it there if youre searching for a switch, in my 90 it sits next to where the shifter is in an unused hole

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That’s fantastic, always love a OEM+ upgrade. Cheers