Wiring Issue '02 Chevy Silverado LT 4X4

[Nickell.Series]

Hi y'all,

I bought this truck last year for a good deal. It was a good deal, but part of the reason it was cheap is that the 4x4 does not work. I replaced the actuator and the control switch--no luck. I took it to get an oil change and a diagnosis for the issue and it was a wiring issue. There's no reason it should not work mechanically on either side, so it's in between. I can't afford to have some dude tear through it at $300/hr. Can anyone here walk me through tracing this wire to where it is faulting? I have the repair manual, but I'm no trained electrician. Other note worthy things: ABS does not seem to work or any other traction management it might have (Making it utterly useless in the snow). I have not touched any wiring except the radio (I did that after the previous issues were already prevalent). The tech at the shop said he checked the fuses and they were fine. 183k odo. Northern truck with expected rust. No other electrical gremlins uncovered after a whole year of owning it.

 

I attached the diagram I received from the tech which highlights 24.1 BN DG[6?] and the R.O.

 

Thanks in advance!

 

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[Ian Mills]

So it won't go into 4hi or 4lo? Is the transfer case shifting? There's a motor and other electronics back there that could be causing you some issues.

As far as ABS and the other stuff, I don't think Stabilitrak was an option on the GMT-800 trucks (someone correct me if I'm wrong) so all you would have other than ABS would be the optional locking differential. How much digging have you done on the ABS?

[Nickell.Series]

Right, it won't go into Auto 4x4, 4-high, or 4-low. The tech that did the diagnosis said the 4x4 actuator was not receiving the signal from the switch. I attached a picture of the thing I replaced, not the whole shift motor, just this little part of it. I haven't done any digging into what's wrong with the ABS. It really could just be the fuse.

 

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[Ian Mills]

5 minutes ago, Nickell.Series said:

The tech that did the diagnosis said the 4x4 actuator was not receiving the signal from the switch.

 

This is very interesting. The 4x4 actuator on the differential is a good first step and it's interesting that it's not getting a signal. I'm pretty sure that the transfer case shifts from 2 to 4 and then sends a signal to the differential actuator after that's successful. Have you checked to see if the transfer case is shifting?

[Nickell.Series]

How do I check that the transfer case is shifting? How could it shift if it's not receiving a signal? I do remember hearing something trying to move when I select 4-low.
On the diagram I got from the tech, the wire highlighted is connecting the "fuse block" to the "front axle actuator".
What is the procedure that the truck goes through after hitting the switch? I'm looking at the description in the manual and I'm not sure I get it. There is a "transfer case shift motor" and "front axle". Is my truck sending a signal to the transfer case but not the front axle?

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[Ian Mills]

Well the transfer case is separate from the differential, so it could be receiving a signal potentially. Before spending hours tracking the wiring, I would make sure the transfer case is functioning properly because that passage of text you attached does say that the transfer case sends a signal after it shifts to tell the actuator on the front differential to engage.

The transfer case is where the rear end of the front driveshaft (and the front end of the rear driveshaft) attaches. It's bolted to the back of the transmission.

Edited October 20, 2020 by Ian Mills

[Ian Mills]

The procedure is:

-Switch on dash sends signal to computer
-Computer sends signal to transfer case

-Transfer case sends signal to computer

-Computer sends signal to actuator on front differential

-You get 4wd

[Nickell.Series]

Okay, I'm pretty confident that the hang up is in step 4, computer to front axle actuator. Can I dig around to see if there's a wire that may be chewed or shorting? I'm just not sure where to look and what two things are connected by the highlighted wire.

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[Ian Mills]

Well you can either start at the actuator and work your way up the wiring harness or at the fuse and work down. At this point I would follow the wires from the actuator end and look for breaks in the wire or a bad ground connection. If you have a multimeter, the continuity setting (ohms, greek letter omega) is going to probably come in handy. Ultimately one side of the fuse should have continuity with one side of the plug that goes to the actuator. If you don't have that, that's your problem

[davester]

Are you sure the TC is shifting in a 4x4 mode?  Easy test is to shift it into either 4hi or 4lo, drive a short distance, then try to spin the front driveshaft.  If it spins, it's not in 4wd, if you can't spin it, it's in 4wd.

 

Edit: and while it might be different for the electric actuator setup, for my '04 Sierra with a manual TC, the sensor in the TC goes directly to the front actuator to move it, it doesn't go through a computer.

 

For my truck, the 4wd harness plugs into socket at the fuse box, that IIRC has power wire, ground wire (actually, this might not be in the plug, but a separate wire that bolts to the frame), 4wd enabled/disabled wire, and 4hi/4lo wire.

Edited October 21, 2020 by davester

[Nickell.Series]

Can anyone tell me what this wire is for? Or how to re-attach it?

Located directly below the gas filler door. It goes into a support under the bed of the truck. I traced it back to the fuse box. 

[Nickell.Series]

33 minutes ago, Nickell.Series said:

Can anyone tell me what this wire is for? Or how to re-attach it?

Located directly below the gas filler door. It goes into a support under the bed of the truck. I traced it back to the fuse box. 

Never mind. I determined that it must be aftermarket since it leads to a dead end at the end of the bed. 

[Wells2000]

I’m having the exact same issue on my ‘99 Silverado 1500. All the lights are on on the 4x4 switch and it seems to be in limp mode. No codes. I tried replacing the switch and the same issue is still happening. I recently changed the transfer case because the old one was leaking. I’ve replaced the encoder motor as well. 
Were you ever able to figure out the issue with yours? I have a feeling the mine is true wiring as well. 
Any help would be greatly appreciated. 

[davester]

...4+ year old thread and Nickel hasn't returned to the site in 4 years.  You aren't going to get a response from that user.