Purchased my H3 last week and on the way home got the Diff Lock light coming on AND the Serv 4x4 light also appeared on the DIC (where the odometer is). So, back to Hummer. After a day in the shop with the tech checking the computer, no definitive answer and no fix. Any ideas? I'm over 3 hours from the dealership and I'm expected to bring it back, again.

Black, Adventure, Auto, no chrome.

Purchased my H3 last week and on the way home got the Diff Lock light coming on AND the Serv 4x4 light also appeared on the DIC (where the odometer is). So, back to Hummer. After a day in the shop with the tech checking the computer, no definitive answer and no fix. Any ideas? I'm over 3 hours from the dealership and I'm expected to bring it back, again.

Black, Adventure, Auto, no chrome.

I purchased my H3 last month and am over 1,000 miles from the nearest dealer. I experienced the exact same flashing light and "serv 4X4" warning light on the dash at roughly 750 miles. Per the manual, I cleared the warning by pushing the odometer reset button. The vehicle now has about 2,000 miles on it and that warning light comes on about every 50 miles or so. I called the service tech at the dealer and he assurred me that this warning will not affect the driving of the vehicle. He sent me a complicated flow chart to try and figure out the problem. I am not an electrician, and most of the flow chart instructs you to check the ohms feed back of various wires. The service tech suggested that the problem is either; short to ground, short to voltage or an open circuit. So, I crawled under the rear axel and inspected the Rear Differential Lock Actuator along with the wires coming in and going out of it. I did not see any bare wires, insulation damaged or disconnected wires. I was unbale to pull the Actuator off of its connection. There must be some little tab to push in order to disconnect it and I didnt want to break anything, plus it is pretty close quarters to be able to get yours hands in there and see what is going on. That is about as far as my technical abilities take me.

I could take it to the local GM dealer here in Cabo, but they have not serviced any H3's yet and I am not interested in being the "guinea pig" for them.

Has anyone else experienced this issue?
Does anyone have an answer for me.
A reply would be most appreciated and if you could come and fix it, I would gladly by you a round trip ticket to Cabo San Lucas.
Thank you,
Lance

Hi lance-n. My H3's problem was eventually fixed (it's a LONG story) by Hummer. I didn't completely follow the explanation on my problem but it boiled down to some wires to a solenoid that actuates the diff lock. The wires were too long apparently and were rubbing inside the diff causing an intermittent shorting. They swapped out some parts that were conected to the wires to remedy.

Hello,
That is great news to me!!! My experience with the warning light hes been intermittent as well. Do you think you could connect me with whomever it is at your dealer that fixed it? Being far away from any dealer makes it hard to get any reliable work done here. Also, the dealer I have been calling hasn't seen that specific problem yet and without having the vehicle to look at, it is hard for them to diagnose. Maybe if I could order the specific parts and have them changed out, it should fix the problem.
Thank you

Lance-n; contact Southgate Pontiac in Edmonton, Alberta and speak to Ed in Service Dept. (780) 435-4000 Hard to say if you have the exact same problem, but the symptoms are similar, good luck.

8.6 Rear Axle Electronic Locking Differential Inoperative - Service 4WD Indicator DTC C0388 - keywords diff G94 HC4 MIL #PIP3593 - (Oct 19, 2005)
8.6" Rear Axle Electronic Locking Differential Inoperative - Service 4WD Indicator DTC C0388
2006 Hummer H3

Equipped with Electronic Locking Differential (RPO - G94)

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
A customer may comment that the SERVICE 4WD indicator is illuminated, and the electronic locking rear differential is inoperative. DTC C0388 may be set.

Recommendation/Instructions:
Follow the diagnosis for DTC C0388 (SI Document ID #1537926). If following this diagnosis determines that the locking coil or pigtail has excessive resistance or is shorted to ground, remove the rear axle cover and examine the routing of the pigtail wires to the locking coil. Inspect for wiring damage that may have been caused by the pigtail being routed too close to the ring gear bolts. If wiring damage is observed, replace the locking coil and pigtail assembly.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

thank you for the contact info.