Gen 4 Factory locker - on any time

[nj swb]

I've seen the question asked a couple of times about engaging the factory rear diff lock in 2H, or presumably any other time.

Looking at the wiring diagram here engaging the rear diff lock seems relatively straight forward - but this is all from looking at the diagram(s). I haven't done any testing, partly because I'm too lazy, but largely because I don't have access to a Pajero with factory rear diff lock.

From the diagram, it appears that to lock the rear diff:
1. the transfer ecu supplies power to the air compressor motor, which presumably closes the release valve
2. a separate pressure switch cuts power to the motor when there is sufficient pressure.

To unlock the rear diff:
1. the transfer ecu cuts power from the motor and release valve, which presumably releases pressure in the system and allows a spring / other mechanism to unlock the diff.

I'm guessing the ecu switches 12 V to the air compressor, and not some lesser PWM voltage. It shouldn't be too hard to check that with a multi-meter.

So that appears pretty simple to organise, except there is feedback from the rear diff to the ecu to indicate that the diff is locked. If this signal arrives without the ecu issuing the lock signal this could cause an error, so it would probably be necessary to interrupt this signal.

The transfer ecu also turns on the rear diff lock light on the dash by pulling a pin to ground. This same pin is connected to HBB, EBD, ABS and ASTC, so it might be necessary to manipulate these wires if you want to illuminate the light without informing the other systems that the diff is locked. Or, you might want the ASTC to know the diff is locked, so traction control doesn't attempt to interfere while the driver is doing whatever it is for which the driver wants the rear diff locked.

Alternative option:

The wiring diagram shows a single input into the ecu indicating that the centre diff is locked. If this is the only pre-requisite for locking the rear diff, it may be a simple as grounding that wire whenever the driver wants to override this factory limitation. Of course, the transfer ecu could get upset with a signal that the centre diff is locked when it's not expecting it to be.

Additionally, I believe there is an inbuilt speed limit, that automatically unlocks the rear diff above a certain speed - attempting this alternative option will still allow the transfer ecu to unlock the diff as it sees fit, which may not fit the driver's requirements.

[Just Cruzin]

I thought the bigger question was engaging 2wd low range for reversing the van.

[Ian H]

What scenario would require the diff to be locked while in 2H ?

To me, diff lock is the last option I have to get me going like I had to on a steep rock climb. But I was in 4LLC by then anyway.

[twisted32]

I've seen the question asked a couple of times about engaging the factory rear diff lock in 2H, or presumably any other time.

Looking at the wiring diagram here engaging the rear diff lock seems relatively straight forward - but this is all from looking at the diagram(s). I haven't done any testing, partly because I'm too lazy, but largely because I don't have access to a Pajero with factory rear diff lock.

From the diagram, it appears that to lock the rear diff:
1. the transfer ecu supplies power to the air compressor motor, which presumably closes the release valve
2. a separate pressure switch cuts power to the motor when there is sufficient pressure.

To unlock the rear diff:
1. the transfer ecu cuts power from the motor and release valve, which presumably releases pressure in the system and allows a spring / other mechanism to unlock the diff.

I'm guessing the ecu switches 12 V to the air compressor, and not some lesser PWM voltage. It shouldn't be too hard to check that with a multi-meter.

So that appears pretty simple to organise, except there is feedback from the rear diff to the ecu to indicate that the diff is locked. If this signal arrives without the ecu issuing the lock signal this could cause an error, so it would probably be necessary to interrupt this signal.

The transfer ecu also turns on the rear diff lock light on the dash by pulling a pin to ground. This same pin is connected to HBB, EBD, ABS and ASTC, so it might be necessary to manipulate these wires if you want to illuminate the light without informing the other systems that the diff is locked. Or, you might want the ASTC to know the diff is locked, so traction control doesn't attempt to interfere while the driver is doing whatever it is for which the driver wants the rear diff locked.

Alternative option:

The wiring diagram shows a single input into the ecu indicating that the centre diff is locked. If this is the only pre-requisite for locking the rear diff, it may be a simple as grounding that wire whenever the driver wants to override this factory limitation. Of course, the transfer ecu could get upset with a signal that the centre diff is locked when it's not expecting it to be.





Additionally, I believe there is an inbuilt speed limit, that automatically unlocks the rear diff above a certain speed - attempting this alternative option will still allow the transfer ecu to unlock the diff as it sees fit, which may not fit the driver's requirements.

In red above, I beg to differ

[nj swb]

In red above, I beg to differ

OK, so I'm too lazy to access a factory rear diff lock.

[nj swb]

I've looked in a little more detail, I think it can all be done with three wires at connector D228, which looks like its on the transmission tunnel, but we might need to go searching for it.

We can even use the detection switch to drive the light on the dash, so you'll get real confirmation that the diff is locked.

First, confirm that the compressor does get full voltage, and not some lesser PWM level. The service manual specifies testing it with "battery voltage", so there's a good chance it's simple.

You'll need a DPDT relay (to make the light work) and a 10A DPDT switch (switch the compressor & the relay). Or a 10 A 3PDT switch, but that might be a little harder to find.

Plus a 10A fused power source to run the compressor, if you don't already have one available.

When the switch is off, factory configuration, works as per normal.

When the switch is on, rear diff is locked, and the dash light should be on. The ecu won't know it's locked, and can't turn it off for you.

Using the factory switch to turn on the locker while it's already on could cause an error code, depending on how the factory system is programmed.

When do you want to do this?

Edit: updated the switch requirements - SPDT switch isn't enough.