there is another site where there are always guys to help.. ones that have been wrenching on these trucks since they first came out.. check out the link here.. http://bfy.tw/3Ttk there is tons of info on the 4wd system over there..So I've read all the posts on this topic and here's where I am at. I confirmed with jiffy lube that all my fluid levels were good as of November when they changes oil. I couldn't switch into anything except 2whi. After some wonkiness, all 4 lights would flash then service 4wd light comes on. Two nights ago, its been real cold, like single digits, I go to drive, usually flashing and service light behavior....I start driving and can feel 4wd is on while turning and the gearing is different. I turn onto a side road and almost have no power, things are spinning but minimal power. I restart the vehicle and both the 4wlo and 2hi lights are on, the switch is on 2whi. I drove back home and it seems to be stuck in 4wlo now. I drove slowly to the store where I was going and could hear 4wlo doing what it does....some diff whining... I put in neutral and it tries to move back to 2whi....but when I gave it gas, it was still 4wlo, but without power again. Fiddled some more and did the neutral thing again and I heard it again trying to go back to 2whi. This time but worked and the light above 2whi is on and the service light is off. I plan to eBay the tccm, as this is what seems to be the problem. The fluids are good, the motors are moving the transmission....thoughts?
I had considerable difficulty removing the driveshaft until I removed one end of the connecting link between the lower control arm and the sway bar, then I finally had enough room so that it all came apart. By the way, I replaced my RH driveshaft this week because the US$ is up against all foreign currencies. My replacement was only $65, the cheapest list price I found was only $48.00. At those prices, my opinion is to throw the old one away or keep for spare.Please read me before making a post.
There seems to be quite a lot of mystery to newer folks when their 4x4 functions stop working. Since crappy weather season is upon us a lot of people are trying their 4WD functions for the first time this year... and discovering all isn't as it should be.
Here's my attempt at a troubleshooting checklist/flowchart. Hopefully this helps folks get a handle on what's wrong with their setup and how to fix it.
Information in this thread applies to 360/370 trucks with selectable 4WD functions (TrailBlazers, Envoys, Ascenders?). Trucks with non-selectable AWD (Rainiers, 9-7s, Bravadas) may find some of the information here useful. However AWD trucks lack some of the parts discussed here.
On to the show.
Gah! My 4WD doesn't work! What do I do?
Is the Service 4WD light on?
Yes: Go to Section 1.
No: Go to Section 2.
Section 1: My Service 4WD light is on.
Are there any lights lit on the 4x4 selector switch?
Yes: Go to Section 2.
No: Try these steps.
- With the ignition off, rotate the 4x4 selector switch from left (2HI) to right (4LO) and back again about 20-30 times. With lack of use, the contacts inside the 4x4 selector switch can get a light amount of oxidation on them. Repeatedly rotating the switch can sometimes clear this problem up. If this doesn't help, read step 2. If step 2 doesn't work for you, replace your 4x4 selector switch. If replacing the 4x4 selector switch doesn't work for you, try to find a local member with a verified working TCCM to swap in. If the problem goes away, return your friend's TCCM and buy a replacement for yourself. Search these forums for replacement instructions.
- On some 2002 model year trucks, the Transfer Case Control Module (TCCM) can have trouble waking up when the engine computer tries to talk to it. Fuse #8 in the engine bay fuse block provides power to the TCCM. Pulling this fuse and replacing it will usually wake the TCCM up and allow the use of 4WD for a time. Fixing this requires either a dealer software update (can be spendy, doesn't always work) or replacing the TCCM with a unit from a 2003 or newer model with selectable 4WD.
Section 2: Checking the motors.
With the ignition on, switch the 4x4 selector switch from 2HI to 4HI. You should hear two distinct mechanical whirring sounds. One from the middle of the truck (under you) and one from the front of the truck.
I hear both whirring sounds: Go to Section 3.
I don't hear the sound from under me: There is an issue with the Transfer Case Encoder Motor. Check the connector going to the motor(cylinder looking thing) on the transfer case for damage/corrosion. The motor may require replacement.
I don't hear the sound from the front: There is an issue with the Front Axle Disconnect Actuator. It is plugged into the Front Axle Disconnect (AKA Splined Disconnect) located under the truck on the right side of the oil pan. Check the connector attached to it for damage/corrosion. If the connector is OK, replace the actuator.
Section 3: Identifying mechanical failures.
Turn the ignition on but don't start the truck. Place the 4x4 selector switch in 4HI. Using a jack/jackstand raise the LEFT FRONT wheel off the ground. Try to turn that wheel by hand.
The wheel does not turn freely: If you've followed the troubleshooting guide without skipping ahead and come this far, then you have an issue that is beyond the scope of this post. Possibilities are an intermittent problem in the Front Axle Disconnect, front differential failure or transfer case failure. I recommend you make a post in the 4x4 section detailing each of the steps in this guide you just followed. Also note any noises you may be hearing while driving in and out of 4WD.
The wheel turns freely:
- Crawl under the truck so that you can see the front driveshaft. Have an assistant turn the left front wheel by hand. Can you see the driveshaft turn? If so, you have an internal transfer case failure. Most likely due to worn out clutches. If not, proceed to step 2.
- It is likely your Front Axle Disconnect is not engaging properly. This can be caused by worn bearings or a broken shift fork. You can check for worn bearings by grabbing the inner tripot joint(closest to the Front Axle Disconnect) of the right side axle and trying to wiggle it. Movement indicates worn bearings. Even if your bearings aren't overly worn, there is a possibility of a broken shift fork, spring, or other components.
There is a great guide on the teardown and rebuilding of the Front Axle Disconnect here: http://www.offroadtb.com/articles/tech-docs/front-axle-4wd-disconnect
There is an alternate way of fixing the shift fork issue here: http://forums.offroadtb.com/viewtopic.php?f=27&t=1227
- If you rebuild/replace your Front Axle Disconnect or are 100% sure it is functioning properly and still are at this point in the troubleshooting guide, you may have an internal front differential failure (likely) or broken intermediate shaft (extremely rare, couldn't find an instance of this by searching). Now is the time to make a post in the 4x4 section detailing all the steps you followed in this guide as well as any other observations made.
There you have it. I hope this guide points you in the right direction.
Guess I never came back with the fix on this. Turns out the +12v wire going to the front actuator was broken 'somewhere', so no power to the unit. Tried to trace it back but why is the fuse/source in the panel under the back seat?? I gave up and ran another wire from a fuse in the engine compartment fuse block down to the actuator. Bingo, been working fine since.So I followed the directions at the beginning of this thread. Transfer case motor works fine. Front axle disconnect actuator didn't make any noise. Pulled it and connected to a second TB I have . Still nothing; great, bad actuator, buy a new one. Install it and still no noise/motion. Take the new actuator to the second TB, plug it in and it works. Put new one back on first TB, still nothing. Connector/wiring look good, no damage/corrosion, wiring harness looks fine. What now? Is there a wiring diagram I can trace back? Bad fuse?