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No response from 4WD buttons

Tiny
RYTHOMAS
  • MEMBER
  • 2003 CHEVROLET SILVERADO
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 250,000 MILES
I just came back to the truck after it was sitting for a year, and the 4-button 4wd dash switch lights up when the key is turned on but doesn't do anything when I push a button. No blinking, no noise, nothing. The 2Hi light just stays lit.

I've had issues with this 4wd system in the past that were fixed by cleaning up the ground on the frame, replacing the dash switch, and more recently replacing the encoder ring and motor. The 4WS, 4WD, and IG1 fuses are all ok and have power when they key is on.

I suspect it's a ground or some other electrical connection, anyone know what would cause this?
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Thursday, December 9th, 2021 AT 3:50 PM

9 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

Allowing a vehicle to sit can certainly cause corrosion issues, especially if it sits outside or where it's damp.

First, I attached the wiring schematic below for the circuit. You didn't mention testing the TREC fuse or the ignition E fuse. I highlighted them below. Their locations are indicated on the schematic.

Next, I highlighted two ground locations to check. Check them as well. Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

Let me know if this helps and what you find.

Take care,

Joe

See pics below.
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Thursday, December 9th, 2021 AT 6:14 PM
Tiny
RYTHOMAS
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  • 6 POSTS
Thanks Joe, I'll check those out.

How does the Z71 g-locker factor into the 4wd system wiring? I've read that it only works in 2wd mode (which makes no sense to me but that's another topic), but I don't see anything in this diagram related to that. It hasn't worked since I've owned the truck so it's a bit off topic for the current problem, but this got me curious about whether that could be an electrical issue as well, and whether the diagram is different for trucks that have it.
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Friday, December 10th, 2021 AT 1:50 PM
Tiny
RYTHOMAS
  • MEMBER
  • 6 POSTS
I checked the TREC and IGN-E fuses, they're both good and have power to them.

I think the TCCM ground on the left front body mount is the one I already checked. But I can't find the ground wire that goes to the "body relay block" and then "near left A pillar". I have the whole dash apart but can't see a ground back in that area.

I'll try testing the pin on the TCCM connector if I can find the right one.
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Friday, December 10th, 2021 AT 3:55 PM
Tiny
RYTHOMAS
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  • 6 POSTS
Update: I think I found the ground; it looks okay based on visual inspection and I hope that I don't have to take it apart because it's really far back and there's no room to work in there.

The TCCM is not where the Haynes manual says it should be, can you help me locate it?

And what should my process be to diagnose the issue from here? What would cause the TCCM to ignore input from the control switch, but still illuminate the 2HI indicator light and flash all of the indicator lights when the key is first turned on? The service 4wd warning hasn't come on since this problem has been happening.
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Friday, December 10th, 2021 AT 4:17 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
As far as the ground, if you can't access it and suspect it can be an issue, run a new ground wire to the component and see if it makes a difference.

As far as the TCCM, I attached a pic below showing where it is located (at least according to my manual).

As far as your questions, there could be an issue with the module itself or even the switch. But I feel if the switch were the issue, the light wouldn't be on.

Let me know if that helps.

Joe

See pic below.
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Friday, December 10th, 2021 AT 7:38 PM
Tiny
RYTHOMAS
  • MEMBER
  • 6 POSTS
Can you point me in the direction of a diagnostic procedure? I don't want to just start throwing parts at the problem.

As a start I'm thinking I should test the wiring between the TCCM and the switch, encoder, and actuator. If that checks out, is there a way to bench test the TCCM or somehow rule it out as the problem? What about the actuator, would I just supply voltage to the brown and blue wires to see if it moves?

The internet is so cluttered with posts from people with similar problems with these systems (and answers telling them to just try replacing things) that it's tough to find any good procedures for methodically ruling out components as being the issue.
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Saturday, December 11th, 2021 AT 11:02 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
The best thing to do would be to scan the can-bus system to see if there is a code stored. CAN stands for controller area network. Basically, all computers/modules are tied together via a few wires. This type of scan would identify codes regardless of the module in which they are stored. Here is a link explaining how it's done:

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

Also, I attached diagnostics below for when the transfer case won't shift. See if they help.

Let me know.

Joe

See pics below.

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Saturday, December 11th, 2021 AT 8:45 PM
Tiny
RYTHOMAS
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Well, I didn't get around to doing any of that diagnosis, just cleaned up the pins and connectors on the TCCM, which didn't have any effect at the time.

But then yesterday when I was running some errands the "Service 4wd" message displayed for a bit, and a couple stops later it went away, and since then the system has been working perfectly. I guess it needed to be warmed up and dried out or something.

I have a CAN scanner and there were no codes before this, but I'll check again in case it stored one from when the message was displayed.
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Monday, December 13th, 2021 AT 10:12 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

It sounds like you got something tightened up and it's now making contact. If that changes or if you run into trouble, let me know. I'll try my best to help.

Also, I hope you have a great holiday, and thanks for the update.

Take care,

Joe
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Monday, December 13th, 2021 AT 2:35 PM

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