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Front Axle Problems - Locking in 2wd?

6715 Views 15 Replies 3 Participants Last post by  65thmatt
Hi Guys,

I am new here, hope this post is in the right spot on the forum.

Some background on my knowledge and previous experience of 4wd operation:
My previous vehicle (2000 S10 ZR2 Blazer) once started making a nasty grinding noise on a out of town trip. I discovered the front diff had metal shaving. Upon finding a basically new one, and having it installed at a shop, it started making the same noise a week or so later. I found out a vacuum problem was causing the front axle actuator to engage partially, causing grinding. The vacuum problem was a combination of a stuck transfer case vacuum switch, and also a small leak on a rotted hose under the hood. I caught it in time to save the new differential.

So when you shift into 4wd, the transfer case motor activated, engaging the front drive shaft. The vacuum switch "ball" gets activated by transfer case internals, (bypassing or transferring?) vacuum to the front differential actuator, locking both wheels into the differential rotation


While in 2wd, my front wheels feel like they are in 4wd, meaning I get "wheel hop" when making a turn. I see that the Colorado now uses electronics instead of vacuum to activate front axle actuator. I assume the sequence is essentially the same though.
What could be causing my front wheels to be locked together?

Axle actuator stuck in position possible?
I see that my front axle seals have been seeping. Maby low on fluid?
Bad transfer case switch?

I have not taken anything apart yet, just stopped driving it to prevent a expensive problem like I had with the Blazer.
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Probably the actuator
Ok, so if the actuator gets stuck in "4wd" mode, does the computer get position feedback to throw a code?

Also, how could I test this theory? Maby put up on jackstands and spin the front wheels?
Not sure if it will throw a code. Does it shift from 4 hi to 4lo?
Yes that is the front axle actuator. But that may not be the problem for sure. Does the 2wd button light up when you try to go into 2wd?

One way to test if you are 4wd hi or lo is to put the truck in park and crawl under it and grab a hold of the front drive shaft and try to turn it. The front drive shaft should spin freely if it's in 2wd. The front drive shaft will not spin if it's in 4 hi or 4 lo.
I would also check all fuses related to the dash switches and 4wd system
You also try disconnecting the negative battery cable for a few hours to "reset" the systems
Is there a check engine light or "service 4wd" message on the DIC at start up?
"Is there a check engine light or "service 4wd" message on the DIC at start up? "


"I would also check all fuses related to the dash switches and 4wd system"

Yes, I need to do that

All lights on 4wd control buttons operate as normal. We have snow here, so I was able to test it more easily. In 2wd, front wheels do not spin when I gas it from a stop. In 4wd, front wheels spin. So, the transfer case is operating just fine.

Looking at those wiring harness diagrams leads me to believe that the axle actuator does indeed have a proving switch. I have no idea what the TCCM does with that information.

I think I am going to take the actuator out, then have a helper switch between 2wd & 4wd and see if the actuator actuates lol.
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Take the actuator out and then hit the button to see if it moves. If it doesn't that's the issue or the wiring. If it does then you have a mechanical issue with the components the actuator engages.
Alright, I will try that this weekend. Thanks for your help guys. I will be sure to post an update, maby help someone in the future.
Took the actuator out, and went between 2HI and 4HI, it moves just fine. Also, I stuck my finger in and depressed the parts that it pushes, that seems to be ok as well. Transfer case engaging properly as well.

I am seeing some oil seepage coming out the axle seals where the half axles go into. I saw fluid come out when I took the actuator out, so I am assuming I have a decent amount in there.

I have the front up on jack stands, neither of the front wheels seems to be engaged. They are spinning relatively freely, a little friction from the half axles at such a steep angle.

I am stumped for the moment.
Sure it's not the rear end? The g80 lockers can get stuck sometimes, and also known for failures that could keep it locked.
In thinking I might be having unintended rear axle lockup:

I put there rear up axle up on stands today. I pulled the diff cover (I am gonna change fluids anyway). Everything looks in order, fluid isn't burnt, no metal chunks. I tested the locker for operation by spinning by hand. I got it to lock both wheels together, a slight jerk in the opposite direction while spinning unlocks the wheels.

Now I get the rear put back together.
I guess the next step is I am gonna pull the front diff cover off.
On a positive note I just got new tires :) Goodyear Silent Armor
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