4WD not working, '01 4WD axle actuator location

[mike2004tct]

I got a new hub actuator, the unit on the fire wall, as it didn't have an output, and caused 4WD lights to flash constantly.
Lights don't flash now, button unit says it's in 4WD, but still have no transfer case engagement.
I want to check the axle actuator tomorrow (after todays snow melts off).

Is this unit under the battery case, as in the earlier models?

[old_master]

Yup, under the battery tray... needs vacuum to it when in 4WD HI and LO. The actuator should pull the cable in and operate the clutch mechanism on the right front axle and cancel the switch at the axle tube.

[mike2004tct]

UPDATE.
Well, got the actuator replaced last sunday, everything works as intended.
Froze my ass off doing it, but I was satisfied with the outcome. All 4 fuctions of the buttons work.

So yesterday, got in the truck and put it in 4WD Hi to go up a snow covered drive, through the plowed in drift, at the In-laws house. . Fine. Shut the truck off. Cleared their driveway. When I got back in to leave hit the 2WD button, and the thing blinked about 15 seconds, then went back to 4WD Hi. Hit 2WD, same thing - blinking, then back to 4WD Hi. Hit 4WD auto next, and it blinked about 10 seconds, then the service 4WD light came on and all the lights on the switch pod are out.

Shut the engine off, then back on. 4WD Hi blinks for ~15 seconds, then all lights go out and service 4WD light go on. Shut off again, restart and hit 2WD right away. Blinks for ~15 seconds, then goes out and service 4WD light comes on. Shut it off. Restart, hit Auto 4WD immediately, and the light blinks about 10 seconds, then goes on solid. 15 seconds later, service 4WD light comes on, but Auto 4WD light also stays on solid. If I then push 2WD, both while parked, and while driving, light blinks for ~15 seconds then all button lights go out and service light comes on. Numerous other scenarios of button pushing, but all have the same result - no pod lights, and Service 4WD light is on.

Sort of a lengthy post, but that about covers it all. I can hear all kinds of clicking coming from the passenger footwell when I push the buttons, don't know if it's relays, or a control module.
Even colder today than it was last week, so I'm not too enthused about working on it , for a few days at least.

????????

[old_master]

Couple things to check:

Make sure the switch on the right front axle tube is not snow packed and that it is working.

There have been "issues" with corrosion on the pins and sockets in the TCCM and its connector. I think, on yours, it's behind the passenger side kick panel. Be very careful as the pins are very delicate. Try using some electronic parts spray cleaner on it, and after its clean, smear a gob of silicone dielectric grease in there.

[mike2004tct]

Thanks for the quick response.
I'll sound a little naive here, but is the kick panel on the fender side, or the firewall side?

My hearing is not the best, and I can hear the clicking from what I think is the TCCM, but I can't pin point from the driver's side.

[old_master]

Kick panel is the plastic panel right next to the passengers feet.

[mike2004tct]

Haven't looked at the TCCM yet, but it does click when I select the different buttons. The truck is stuck in 4WD Hi right now. 2 y/o battery died today, don't know if it's related to these 4WD problems, or just a bad battery. (My luck sux).

So anyway, I put a new battery in tonight. Took the tray out, and noticed the actuator was engaged. Disconnected the vacuum to release the cable. Cable moves freely. So put the battery in, and it's still stuck in 4WD Hi. switch to 2WD and the light flashes, TCCM clicks, then light switches back to 4WD Hi. Trieid switching between 2WD, 4WD Hi and Lo, and 4WD Auto. All positions reset back to 4WD Hi.
Maybe tomorrow I'll drop the panel under the glove box and find the TCCM.
I am not optomistic.
Never heard a peep out of the TC Motor, so I'm starting to suspect the motor. No code light right now, so maybe it'll show up tomorrow. I'm probably going to take it in, as my cheapo scanner is just that; only good for SES trouble shooting.

[old_master]

With the engine at idle, make sure the vacuum actuator does not have vacuum to it when in 2WD. Maybe disconnect the vacuum line to the actuator and try shifting to 2WD, it could be that the vacuum switch on the transfer case is stuck, applying vacuum all the time.

[mike2004tct]

Originally Posted by old_master

With the engine at idle, make sure the vacuum actuator does not have vacuum to it when in 2WD. Maybe disconnect the vacuum line to the actuator and try shifting to 2WD, it could be that the vacuum switch on the transfer case is stuck, applying vacuum all the time.

Took a look at the TCCM (MDC ASY) yesterday. All pins are ok. Crawlwd underneath and checked the TCMotor, all connections ok there too. Also checked the speed sensor on the RF Axle tube, no snow or corrosion there either.

The unit is stuck in either 4WD Hi, or 4WD Auto. It will not shift back to 2WD.
Any time I select 2WD, it blinks then defaults back to 4WD Hi. Because I don't want to drive around in 4WD, I put it in 4WD Auto, and after about 50 feet of movement, the Sevice 4WD light comes on.

Because it won't go into 2WD, I wonder if the cable is not releasing the lock-up shaft?
But then why does 4WD Auto cause the light to come on?

I disconnected the firewall actuator to the actuator ubder the battery tray, and it still won't go into 2WD.

I'm stumped on this one.
I'll try manually pushing the cable back in, and leave it disconnected from the actuatur and see what happens.

[mike2004tct]

OK, checked actuator under the tray agian.
With engine running, I disconnect vacuum, watch the cable release (about 3/4 to 1" travel), tried switching to 2WD - light blinks, then goes to 4WD hi and stays blinking. Still won't go into 2WD. Buttoned everything back up so I could move the truck slowly while switching, still no luck.

2 weeks ago I had 4WD Hi and Lo. It won't go into 4 WD LO or 2WD. Today with the 4WD Hi light on, I only have rear wheels turning, even though the cable is actuated (pulled out).

Can the encoder motor being stuck/dead cause this?
I don't want to chance replacing it (NP8 setup) as it's rather pricey for a rebuilt ($250.00)

Also of note, I have the older (original) TCCM, #15748800. GM no longer makes this, and it's superceded by 12577412.
On "The Other" site, I found a thread about being stuck in 4Hi, with encoder testing, as well as manually shifting the shaft the encoder hooks up to.
That guy ended up solving his problem with the newer TCCM. Claims less clicking with the newer unit.

[mike2004tct]

Found the problem to be the Transfer Case motor. What a headache this has been.
Here's the results;

http://www.automotiveforums.com/vbul...09&postcount=6