had to use my rear locker while offroading the other day but couldnt get it work.
going up a slope,rear right started spinning,put in neutral and hit the diff lock button.
light came on but didnt hear anything,when i hit the gas the rear right was still spinning!
tried a few more times but reversed out.
am i doing something wrong or do i have a problem?
there are no trouble codes on the display.
if there is a problem,can somebody please advise were i should start checking,is there a fuse or relay i should check before taking the diff cover off?
pls advice!
thanks

 

Have you tried the rear locker since then?
sometimes it take a few second for the locker to engage and won't if teh internal parts aren't lined up properly

If you are moving while trying to engage the locker make sure you are going in a straight line andnot spinning your wheels.

 

Nicos....whazzz up brud.

Desert Dan has a good point. The locking pins have to be lined up for it to engage, and it does take a second or two.

I also noted you said you tried to engage it from neutral? T case neutral, or Transmission neutral? The T case has to be in 4Lo Lock
or the rear diff will NOT lock up.

From the manual:

To lock the rear axle, do the following:

1. Place the transfer case in the 4LO Lock mode. This is the only mode which will allow the rear axle to

lock. See

2. Press the button with the vehicle stopped or moving less than 2 mph (3 km/h).

You must wait for the light in the button to stop flashing and remain illuminated before the rear axle is locked.

Notice:

If you try to lock the rear axle while your vehicle is stuck and the tires are spinning, you

could damage your vehicle’s drivetrain. The repairs would not be covered by your warranty.

Always lock the rear axle before attempting situations and/or navigating terrain which could

possibly cause the vehicle to become stuck.

The locking rear axle will be disengaged when the wheel speed is greater than 20 mph (32 km/h), if the

vehicle’s battery is low and/or the transfer case is shifted out of 4LO Lock mode.

 

But nicos said the light came on. That should mean he did well. But I also would try it again on plain surface without hitting the brake. For giving a bit movement to the locker I would let the truck roll very slow...

 

guys i did all the above,a couple of times!still doesnt engage and what worries me is that im sure i could hear it engaging before.
i am in 4lo lock when engaging in gearbox neutral not transfercase neutral.
i think there is an elecrical problem.
can someone pls advice if there is a fuse/relay i can check?
also were is the control unit that sends signal to the rear diff?
thanks for all your help!

 

First - you do not need to put the t-case or tranny in neutral to engage the locker. You just need to have it 4lo.

If the light is coming on (and staying lit) then the problem is not likely electrical. The locker is controlled by one of the computers (BCM, PCCM, whatever). If the switch lights, then the coil is energizing. If you're still not getting power to both wheels, its likely you've rounded over or broke the pins on the locker. Warranty time.

 

I guess that would be something you could hear. That should make a hard ratteling sound. Where is the sensor located which sends the information that the locker is locked? Or is there no sensor, is it only a signal from the BCMonly to indicate the locker is adviced to lock? In this case I would check the voltage directely at the locker to check if it's activated while pushing the button.

 

I don't see any reference to it in the BCM or PCM wiring. It may be handled by the transfer case module (behind the cover on the passenger end of the dash).

 

i tried it again today but reversed a bit as soon as i hit the button,i think i heard a slight clunk so may be it engaged!
i will try it offroading on the weekend to make sure.
what i dont understand is that the light on the locker button comes on immediately when i hit it,no flashing.
shouldnt it flash like the low lock button and stay on when its properly locked?
if say i was in a situation were i am in low range trying to go up a hill and get spin on one of the rear tyres,should i hit the diff lock and reverse a bit then try again or should i just hit the diff lock while stopped and go(as i did last time but diff didnt lock)
sorry for asking its just that my previous truck didnt have a locker and i havent used the H3 on sections were the locker was needed until now!
thanks again for all the replys!

 

I was reading somewhere that it's ideal to engage the locker prior to a wheel spin condition. Once the wheel has started spinning it can sometimes be difficult for the locker to engage? Or maybe they just mean the obvious that you don't want a spinning wheel condition to begin with.

Quote from the following site: "Ideally, differentials should be (manually) locked before traction is lost and wheels start spinning."

http://www.4x4abc.com/4WD101/diff_locks.html

If you anticipate losing traction at some point on the trail, it would make sense to engage it prior. Whether or not that would effect the engagement process after a wheel spin condition I'm not sure (I doubt it). I don't have any literature as of yet as to how the Hummer lockers excatly work...