Rear Diff Lock Anytime Mod 3rd Gen DEVELOPMENT

Thread Update (11/4/2020)

Still no update for an elegant anytime locker for the OR/Pro.
However I have supported several people who have installed the OR/Pro locker in their SR/SR5/Sport/Limited, and have wired up the locker.

See Threads here
https://www.tacomaworld.com/threads/2017-e-locker.585669/
https://www.tacomaworld.com/threads/factory-locker-install-on-16-sport.692802/
Thanks to @fuzzydoodle and @traumahawk for their assistance.

Thread Update/Summary (3/20/19)

I have ceased all 'active' work on Anytime Rear Lock for the 3rd Gen.
The end result was failure for me (for a relatively simple elegant solution), however I will admit that alot was learned in the process, that may still pay dividends in other areas for myself and others.

I will still generally try to support questions people have (to describe what didnt work), and please feel free to post in this thread if you want to continue working on it.

The original first post will be archived down below this Update.

Main Points that we learned (Stuff that works):
The spring-loaded lock coil engages only when power is applied, and releases when unpowered.
Toyota uses a PWM controller inside the 4WD ECU to power the coil, with a higher power until it detects a lock, and lower power once locked.
It appears that applying the higher power constantly is probably fine, but I would not recommend applying full 13-14V line voltage to the coil.

Two main options to actuate the diff lock coil have been identified:
The lock coil may be powered thru 12V with a large power resistor (with a heat sink) for a more robust but a bit bulky solution.
For this solution I would recommend approx 1.5 ohm, 100W or larger resistor in series with the lock coil. Resistor will require a large heat sink, maybe a computer CPU heat sink, etc.
ON THIS SOLUTION YOU SHOULD INCLUDE A FLYBACK DIODE, AS THE COIL IS A GIANT INDUCTOR AND WILL CAUSE VOLTAGE SPIKES OF UP TO 10 TIMES BATTERY VOLTAGE WITHOUT THE DIODE INTO YOUR SWITCH OR RELAY. Overkill but recommend 1N5401 or similar.
thanks to @traumahawk who did invaluable bench testing for this solution
Alternatively, use PWM controller for more delicate but efficient solution. Recommend just setting PWM to approximately 70% power or so.

Connectors that mate with the 4WD ECU were found and verified functional (ones I got I had to do some trimming to make them work on my truck).


What we learned DIDNT work
All attempts to spoof the ECU for anytime lock failed.
Attempted to make the ECU think it was in a 2wd truck, failed.
Attempted to make the ECU think the truck was in 4lo when in 2hi, failed. (Note, this can probably be made to work, but probably requires first spoofing 4hi, then spoofing 4lo... one after the other)

End Update
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[Original Post]

I have got numerous requests to work on a Rear Diff Lock for the 3rd gen, especially in my 2Whl Lo Mod thread . So I will put a bit of effort into it, but I am just not as excited about this one personally, so I will need some help on this if I am going to put any further work on it. I may not even do the mod myself if we figure it out... If people really want this, then lets work together on figuring it out.

So, firstly, what (if anything) has anybody actually tried to do to get it to work on 3rd gen? While I was in the 4wd ECU, I tried disconnecting the CAN connection wires on the 4wd ECU and open the 10 amp 4wd fuse. This makes the 4wd (with rear locker) wiring schematic appear pretty similar to the 2wd (with rear locker) wiring schematic (except about 20 sensors). I had hoped that the ECU might then permit lock in 2hi, as the 2wd models don't have 4Lo. I might have done something wrong, but all I seemed to do was piss off the truck with CAN comm failure, so I gave up on that direction.

Therefore, I assume tricking the computer into engaging the locker itself in 2Hi is probably a non-starter, so we will need to lock the diff ourselves I think is the only solution.

Which brings us to the actuator itself. I didn't have a locker on my 1st gen, but looking at the pictures online it looks like the 1st-2nd gen locker was a small rotary motor that actuated the diff lock by way of a threaded shaft. With this system, it looks like voltage can be applied with a relay to control the actuator and use feedback from the set of position wipers built into the actuator. This locker appears to require about 12v to operate, and reverse polarity to the motor to disengage. There was a separate lock/unlock sensor to operate the dash lights, etc. Does anyone know if this is correct?

For the 3rd gen locker, it looks like an electromagnetic pancake, without position wipers, totally 100% different from the previous design. It maintains a separate lock/unlock switch. The ECU monitors the amperage applied to the coil and adjusts it based on some feedback from the lock/unlock switch at a minimum. Using techstream only (and so who knows if the units are correct). The ECU applies about 4 amps to the coil when it is attempting to engage the lock but the lock/unlock switch shows unlocked state, with 77% duty cycle on the circuit. (I assume 77% on a PWM circuit). When the diff changes to locked status the ECU reduces duty cycle to about 50% and shows 2 amp coil current. When the diff is commanded to be released, the ECU indicates just that the commanded current goes to zero. So I assume that the coil defaults to free condition when current is removed and the gear locks appropriately demesh. Does anybody know any more about how the 3rd gen lock coil works? Doesn't seem to be many specs in the schematics or service manual.

Anybody willing to go check the disconnected coil resistance with an ohmmeter? Anybody willing to go jack up the ass end of their OR/Pro and with it locked, and then disconnect the lock harness and see if it automatically unlocks? Anybody willing to lock their ass, and then shut off the engine to see if it unlocks? Anybody willing to temporarily hook some jumper wires between the truck harness and the lock coil, and independently measure coil voltage, polarity, and current while attempting to lock and once locked to see if it matches the Techstream data? Anybody willing to reproduce the techstream data that I got?

Got any takers for assistance?

 

@BigWhiteTRD Send me a PM if you want to talk more offline, but...

I can reproduce the Techstream data tonight, or at least try to...I'd normally be more than okay with doing some of the other tests but New England just got hammered with a ton of heavy wet snow and I will not be back in a garage until this weekend. I have all the tools you'd need to diagnose, except an oscilloscope.

I think the only way to make this mod work going down this path would be to recreate the PWM signal output driving the existing solenoid/whatever mechanism and tie into the existing overhead switch (momentary, BTW). Then you'd have to do more wiring mods with a multi-pole relay to be able to switch between the original PWM signal (for proper operation) and the fabricated PWM signal (for bypass operation)...or you can just get rid of the "proper" way altogether.

I wonder if you can get it to lock just by sending it a constant voltage and leaving it. Maybe that would cause it to overheat.

Only downside to this is I don't think the dash light will work...

I think your 2LO mod is actually a better way of making this happen. You can reach pretty reasonable speeds in 2LO, especially considering the inside of the door says not to fuss with the locker in excess of 5mph. And it retains all of the "factory" function, like dash lights, etc.

 

yes please!!!!!!!!!!!

 

I think probably replace the 'normal' way altogether will be easiest, or at least I can't think of any elegant way to do it without using the '4lo engaged' signal from the 4wd ECU and a bunch more components...

Right now, I am assuming you are right on the PWM duplicate signal. Just too much to wonder about why they are playing with the duty cycle. If is a magnetic pancake of some kind, then I assume it may exhibit different resistance open and closed as well, but that may be more for large a.c. coils and relays. (Not so familiar with DC coils)

Dang, forgot that switch is momentary. They are not out to make it easy.

 

The lock/unlock position circuit appears 100% independent of the control circuit. Probably the first thing to see would be what happens when the computer shows locker is locked up but it is commanding unlocked (like if we hijacked the lock control circuit with a homegrown PWM signal to force a lock)

Unfortunately it might throw a code, (truck loves throwing codes when you hijack stuff), but if we are lucky it will be a multi-trip failure check, because it can take a long time to unlock normally sometimes unless you give it the s curves.

I would rather keep the ECU in the loop so that it can disable ABS and TRAC. IF (fingers crossed) that works the locker symbol on the dash will flash whenever the mod is active...

 

SUB'DDDD

 

I don't think it would error out, or throw a fault code. I locked the differential, and then commanded it unlocked (while it was "bound" in the locked state), and watched it sit there and blink. For minutes and minutes, at least. Seems longer than any reasonable timeout period. That could be promising...

EDIT - the truck won’t let you shift out of 4LO until the locker is fully unlocked. That’s a problem...it’s relying on the 4LO shift completion as a condition for the locker to lock, and vice versa.

 

Will maybe briefly investigate what the computer will do with locked rear switch in 2hi, etc tomorrow. Here is the diff control circuit data...

 

So the NO circuit looks like essentially nominal voltage at reduced duty cycle. Wonder if it will lock in at the lower duty cycle only... maybe just a little harder to get in.

I think maybe the mode lockouts aren't the end of the world. If you are in 2hi, with any time locker active, you have to deactivate it, change 4wd, then reenage. Not ideal, but not disaster, maybe.

 

sub'd. I would help if I understood what any of this meant.

 

I really hope you guys can figure this out. I may not use the mod often but it sure comes in handy. How ever it works out even switching back and forth in and out of 4x to trick it into doing what we want would be worth it. I was honestly hoping when I bought this truck back in 2015 that grey wire mod wasn’t gonna be one of the early ones for me. Not quite so but again if you guys can pull it off there will be many happy taco owners.

 

Mode lockouts aren't the end, but you would just need to additionally trick the lock/unlocked status to make it THINK it is unlocked while you are actually supplying a signal to lock the solenoid.

 

I am thinking let the ECU keep thinking it is locked per the lock/unlock signal, even when we intentionally lock it without permission (maybe). that way the ECU will force off ABS, etc.
Assuming you are in 2hi with diff lock on, and wanted to switch to 4hi with diff lock on, it would mean turning off diff lock, changing to 4hi, then turning diff lock back on. But I think it might be worth it to do it that way, if it means keeping the ABS, etc off for sure.

Going to go try out spoofing the lock signal to ON and see how the truck behaves, if I can get away from the phone...

 

I hate pulse width modulators...

 

Very cool! I would love this mod. I mean, I think I know why Toyota made it to lock only in 4lo, as a safety precaution, but being able to lock the rear at will would be very cool.

 

Doubt I can help but would love this mod. I’ve found locked in 2hi to be pretty useful with other trucks.

 

Hey, not to take this off topic from the circuit logic and design, but you mention that the actuator is different in these third gens. Do I understand that it’s linear rather than rotary? I had a rear e-locker (and front in fact) on my old 80 Series Land Cruiser and I find the 3d gen locker much more stubborn to engage. Could this be the solenoid design, or the mechanical bits, or just random variation between rigs?

 

Don't know for sure. Probably because the old design had a worm drive (which creates pretty large axial forces), where the 3rd gen appears to be a magnetic coil, which probably has less axial force.

 

@bradshawnh
It looks like my idea of keeping the lock/unlock signal to the ECU looks like not a good idea.

To test, I just disconnected the rear diff lock/unlock sensor connector and spliced in a wire to a switch. In 2wd I activated the switch to simulate Rear Lock Anytime with the lock/unlock signal still to the ECU. The rear diff light blinks (after a time period) and 4wd mode changes eventually are prevented.

ABS and TRAC are NOT prevented even though the rear diff lock light is blinking.

Rear diff coil ohmmeter is 3ohms on my meter when not locked.

 

Yet another opportunity to re-gear So is the 3rd gen normally unlocked, by a spring, and locked with the current through the solenoid overcoming the spring force?