This is from the service manual for 2013.

When the operator sets the Mode Select Switch (MSS) to either 4L, 4H or ON position (depending upon vehicle option content) to activate the ELD , the ELD icon displays in the Instrument Panel Cluster (IPC) message center. If the vehicle is driven above the disengage speed, the IPC message center no longer displays the ELD icon, alerting the operator that the ELD is disengaged. Once the vehicle drops below the re-engage speed, the IPC message center displays the ELD icon again. If there is a malfunction with the ELD system, a "CHECK LOCKING DIFFERENTIAL" message is displayed in the IPC message center, letting the operator know the ELD is not engaged.

The differential locks when a Pulse Width Modulated (PWM) controlled magnetic field coil located inside the differential energizes. A collar within the differential moves toward a differential side gear and engages a dog clutch within the differential. This locks the differential side gears and creates the locked differential.

The Transfer Case Control Module (TCCM) activates the ELD . When the ELD is engaged, the TCCM sends PWM voltage to the ELD field coil located in the differential. This voltage is initially 98% duty cycle, and then tapers off to 40% duty cycle after 30 seconds. In order for the TCCM to activate the ELD , certain conditions must be met.

TCCM Input Conditions
MSS set to ELD position
Average rear wheel speed versus average front wheel speed must be less than 15 km/h (9 mph) (via High Speed Controller Area Network (HS-CAN) communication from ABS module)
Operating range (voltage between 9-16 volts)
DTC setting range (voltage between 10-15 volts)
Ignition in the ON position
Throttle Position (TP) less than 50%

 

Thanks for the info - although you can engage the diff lock when in 2WD. It looks like a lot of parameters have to be met.

I'm curious as to why the coil field is initially sent nearly 100% of (whatever voltage is it) and then after 30 seconds it drops to 40% of voltage. Must be the initial burst helps force the dogs together, and then once they are engaged, the 40% is just enough to hold it together.

 

Thanks Chris, good info.

 

There is nothing that says you can't engage it in 4x2....

When holding a coil/solenoid the voltage is reduced to lower temperatures and increase lifespan.

 

This line implies the ELD is switched on by selecting 4L or 4H, which it is not, nor is that a requirement. No big deal.

Tom, it very well still could be simple 12V to the coil actuator inside the diff - PWM is simply used to vary the strength, presumably to allow the drop to 40% of 12V after the initial 30 seconds. Presumably there are MOSFETS in the Transfer Case Module which are supplying the voltage, and can detect the plug being disconnected, hence the message I saw.

For JetExpresses case, I was wondering what the prolonged affect of supplying a steady 12V (assuming that is the correct voltage) would be on the life of the coil. I guess he could install a switched resistor to lower to load to about 40%, but that would be a bit inconvenient. Maybe he's better off just getting an ARB or Detroit.

 

Don't forget the "or ON position"

 

The "On" position refers to the trucks that have the ELD but are either 2WD or 4WD with the manual floor shifter. In this case, the ELD is activated by a simple **** which has an "On" and "Off" position.

For trucks with electric 4x4 shifting, the ELD is activated by pulling the **** outwards and has no marked on or off, just a symbol.

 

This is all great info! Thanks for the research by all.. I'll have to talk this over with my electrical engineer buddy and see if he has any ideas on the duty cycle comments.

With the command coming from the TCCM, I'm curious if the module is different between electronic t-case and manual t-case trucks. And if there isn't a difference, can I just plug and play?

 

At least the functionality of the module is different, but even the manual t-case still has a control module.

 

This is my main concern right now. I think either option (ELD or detroit) is gonna cost the same but if I can't wire a separate switch with the correct voltage or get the factory module to control an OEM locker, then that's out of the question.

 

A Detroit auto locker will cost you less. You can pick it up off the shelf, have it installed, and be on your way. Whether it's the best possible solution for your usage or not, I don't know, but it will be far simpler and almost certainly cost less.

 

Not so certain on that, around $560 from summit for the diff and then price of install kit and price of a good installer. I think I'd be close to the $900-1000 range. Is that about what it'll be? Or is my info source wrong??

I've found a used axle assy from a junkyard with ~6000 miles on it (front end wreck) for $1350. Really aren't that far off...

 

Not sure what year and truck that axle is from, but if it's truly 100% (check EVERYTHING, ensuring axle tubes are straight, all bearings and seals are still operational, pull the shafts, and open the diff with something to catch the oil so you can inspect everything in-depth), AND the gear ratio in it already happens to match the one you'd be swapping out, then that's a screaming deal.

And yeah, you could budget $1k for the Detroit, installed, and be close to the mark either way. Difference is you know that will work and requires no custom wiring and switches and such.

PS On the donor axle, you could seriously consider simply applying direct 12V current to it, if it's anything like the Eaton E-Locker.

 

I know this is a totally different system, but that is exactly what I did with my Jeep when I put Rubicon take-off axles under it; just ran a fused, switched 12v wire to each differential, and voila.......sesctable e-lockers....and never had a moments trouble with them, and they got used......a lot!

 

Jet Did you ever figure out a solution to getting the electronic locking diff?