Rear Diff Lock Anytime Mod 3rd Gen DEVELOPMENT

Hello, new guy here. I've read this (and all linked threads in this thread) probably 5 times front to back over the last few months and it finally came together today when I did my mod. Just wanted to say thanks for all the work everyone's put in, my dumb ass never would of gotten it as clean as I did without some of the diagrams and photos! Really proud of this mod.

The wiring at the axle with the relay and resistor and diode piggybacks in with no cutting using factory connectors. It pulls switched [and fused] power from the trailer wiring circuit. Signaling is done through the factory wires from ECU -> rear of truck. Custom switch circuit board with custom made button cover.

I still have ambitions to take over the dash locked light, I know it's controlled by an output from the ECU and we can't trick it but perhaps I can just drive it directly from the feedback switch in the rear end... I also need to take the switch back apart and make the "on" led red or orange so it's differentiated from the blue illumination LED but for now it's done and working!

 

Very nice work with sealed connectors.

If you want a sealed relay too, I can help some there.

I can probably source the connectors too if you have the numbers. Decent chance I have them in stock.

TLDR, if you have a solution with a spec I can probably make it a bit pretty if you care.

 

Looks great
Really interested to know how the single 1.5 ohm resistor does (if it gets way too hot). Lately I have been recommending (2) 3 ohm resistors in parallel to just reduce the heat in each resistor, but that may be overkill so your experiences will be greatly appreciated. If it does get a bit on the warm side, you may consider just adding a section of aluminum plate for a heat sink.

Just to clarify, I am not smart enough to reliably do any spoofing on the dash locked light.
Right now I assume you still have the rear locker position switch connected to the 4wd ECU. You MAY find that if you drive long enough with the locker manually engaged, that the 4wd ECU will eventually throw a code. (that is what i found when doing driving tests with my locker feedback switch spoofed, but it took quite a bit to get it to throw the code). That is the problem I encountered when trying to use the 4wd ECU to provide the locked diff signal to the dash.

At this point, my best guess is that we need to inject a dummy signal (from a raspberry pi or something) into the CAN saying the rear is locked, which should activate the dash locker symbol. BUt that is beyond my skill set to even attempt (without a bunch of learning), so that is not likely to happen right now (by me).


If any of that made sense.
But again, great job.

 

I have disconnected the lock position switch at the ECU so it doesn't know anything's up. My plan, as rudimentary as it may sound was to just open up the gauge module and physically run wires to the indicator light, even if that mean running tiny gauge wires to individual pads on the circuit board (one of my niche hobbies is PCB design and building and micro soldering and electronic junk, though to be clear it's strictly a hobby, I have zero formal training, I do trees for a living) so I'm not to worried about that, just need to do some diagram studying (quite possibly a few more months worth lol) before I get around to it... Other mods are waiting in the mean time so it'll probably get back burnered, I have a working on demand locker, don't need to get all boujee with it!

I have a heatsink ready if needed but I have faith, I'll keep an eye on it though.


@BigWhiteTRD Thanks again man, without you doing all this I'd probably have just ran batt+ to it through long heavy gauge wires and a relay cutting the factory plug off and soldering straight to it. For sure I wouldn't have thought of the flyback diode. You did all the work so I could have a nice simple elegant solution.

 

Sounds good, if you get around to it, let us know how it goes.

 

Quick question, probably covered before: should we not use A-TRAC when we have the rear locked?
Seems like that’s a no-no to have ABS activating on one rear wheel but not the other when it’s locked.

 

Doesn't matter. A-TRAC would not attempt to brake a wheel because it would never detect any slip left to right with the diff locked. On top of that the skid control ecu knows the diff is locked anyway so it behaves accordingly and isolates intervention to just the front in that scenario.

 

Concur with @ShimStack response.

How has your rear lock mod been working?
Any weird behavior?
Any issues, how hot on resistor, etc?

 

Not doubting your answer, especially since BWTRD concurs but in this case with manually controlled e lockers how would the ECU know?

@BigWhiteTRD
It’s been working wonderful, I’ve had a couple trail rides in the past month where I had it locked continuously for 4-5 hours (working it hard non stop that whole time) and never had a hiccup or any heat or any inkling that anything was wrong! I’d say it’s a total success!

 

As best we can tell, ATRAC just checks LH wheel speed against RH wheel speed, on each axle independently. (So should be no activation on the rear when locked due to the detected wheel speed)

But for you, you are right, no lock feedback, so ecu knows not.

 

Yes, if you divorce from the factory control system it won't know it's locked. But in that case it holds true that there will be no slip across the axle and thus no intervention from A-TRAC.

I've written up a full description of how a locked diff affects fundamental function of the VSC and TRAC systems, just never posted it. For both A-TRAC and TRAC there's really zero concern.

 

Any update on this? How is it functioning? Any error codes?

 

@Cereal_killer installed his mod ~Jul of 21, and provided update ~Feb of 22 as shown below

 

Bump

Anybody wiring and selling this as either a parts kit or complete harness yet?

 

I had a 2005 PreRunner OffRoad and having a locked differential with 2WD got me to a lot of places.

It is beyond frustrating that a 4wd Tacoma cannot use the diff lock unless in 4lo.

 

dont think ive seen it posted but is there a full parts list of what i need to order? had my 3rd gen for a month now and its one of the things i miss the most about my 1st gen truck despite many people saying "why would you ever want a locker in 2wd"

 

See previous post below.

Its really just a question of how you like to splice into the factory wiring and how do you want to supply power... There are too many variations to discuss every option. Do you want to just cut wires, or do a factory replacement connector? Do you want to use the overhead button (which is not a latching switch and therefore is alot harder to use for this job because you need a latching relay) or do you want to use a new latching switch or switch-pro, etc. Other than that, to match the factory ECU output its just a flyback diode, a resistor to drop the voltage a bit, and the question of if you want to display locker status.