Service 4wd light

[battmain]

Got the dreaded service 4wd light on the way home, just cruising along in 2wd. I was running with the dash lights dimmed. That dimmer sure gets hot! Truck would not go into 4wd high when I tried to move the trailer. Did a search and one of the posts said it was the dash switch. And another of the posts mentioned a diode in the switch. Has anyone repaired one of these switches? 50 bucks for a new switch will get expensive every 28k miles.

[AKDmax]

I took mine in for that. "Operates to manufacture specifications." They wouldn't do anything until it throws a code. That's service for ya...

[battmain]

Well, it's working fine today. Stopped at a light, I dropped the tranny into neutral and proceeded to switch between all modes and it's working fine. I'll try later when I turn the lights on to see if it makes a difference. It seems that both times I had trouble was at night when the lights were on.

[NickLeinonen]

i had a problem with the 4wd on my pop's 99 silverado. the transfer case would shift [lights on the push buttons would flash] but the CAD in the front differential would not work. so i grabbed my multimeter and measured my actuator wiring on my tahoe and then measured. he appeared to have a broken wire that was the ground cable [lower left pin iirc?] so i spliced in a new ground wire through a 2A fuse and then tried it. worked perfectally then..

[Tommy turbo]

There should be a code in the computer's memory. There is a ground problem that will set a code. Hard to get to ground to tighten behind vent and instrument cluster but adding a good ground will fix it if that is what it is missing .

[AbqGeorge]

battmain,

yep, had the same thing. Mine would come and go. It (SERVICE 4WD) usually came after running down the road for awhile. It was the dash module. You would think it's just four switches with five wires, right? Nope has a couple of diodes, some sort of solid state module, and precision resistors. Hopefully, they are beefing this thing up so you don't have to keep replacing them.

The manual says that once you get the SERVICE Msg, the TCM goes into a "protect" mode and not permit any response to pushing on the buttons.

AKDmax,
Any problem with the module should throw a code. However, if the tech just looks for engine codes and not for TCM codes, he won't find any.

Another characteristic of mine was that the LED on the 2HI button would be significantly dimmer than normal??

BTW, this problem was with my 2001 and not the new truck in the sig smile.gif

[DMAX Daddy]

Mine did this too.

My dealer said there was a software upgrade for this but they didnt have it yet. Not sure whether I trust them or not...

[battmain]

I hooked up the scan tool and there are no codes stored. Of course, everything worked fine this morning. Yesterday, it would not go into 4wd high. Didn't notice any difference in the intensity of the selector lights. After the last trip on Friday, I left the dash lights bright and the switch wasn't as hot this time, so may have something to do with the heat. No service 4wd for that trip. I'll keep the scan tool with me to see if I can catch an error code.

[saphauler]

Hello all - My 01 gmc had this problem when I bought it (used).

The 2wd indicator light was dim or not on at all and service 4wd would come on when pressing any of the 3 buttons.I then noticed by pressing on the dash next to the buttons the indicator light would come on and go off depending on where you pressed.

Took bezel off dash pulled out switch assembly and when wiggling wires going to switch had the same intermittent effect.

The problem ended up being the switch assembly I fixed it myself ( I try to avoid dealers and have a lot of experience with circuit board repair).

The actual problem was a cold solder joint where the header was soldered to the board.I simply resoldered each pin of the header making sure to apply ample heat to each pin. This is a very common problem with circuit boards because the pins of the header are big and they dont heat up as fast as the rest of the components.

Its been 3 months and all is well with this switch now.

[AbqGeorge]

So saphauler,

You've had the switch apart, eh? Thanks for the tip.

A guy with a 2000 1500HD came by to look at my 2001 (2500HD 6.0L is for sale) and his first question was, "How many times have you had the 4WD selector switch replaced. He was on his third one and it was now out of warranty.

When the switch in the '03 goes, think I'll check the resolder business.

BTW, the manual shows about 3 or 4 resistors, a couple diodes, and a three or four lead "part" inside the switch. You didn't happen to notice what this part is did you??

[4x4TX]

anyone have a part number for this?? I thought I had found the right part number of 15709327 but gmpartsdirect.com said that wasnt it?? Mine has been doing the on and off of the message for 6months and my light on my 4x4panel will go completely out...I have 45K miles so I am guessing they wont fix this underwarranty?? :confused:

[battmain]

Took it to a local dealer and they swapped a 'mode' switch. The part number listed on the invoice is 15063844 then on the next line it shows 1301/69534. Don't know if they are supposed to be together or what. I asked if there was any chance of getting the old switch back, but they told me that they had to keep it because it was fixed under warranty.

As for the tranny whine (not an allison)...As usual, they claim the whine is normal. It doesn't matter, if I tell them it wasn't there before the last tow. Thought I'd go back to the other dealer that treated me right the first time, and now they claim they won't do transmission work on the weekends anymore. Oh well, I guess that was a one time treat the customer right deal when I took it to them on a Saturday. (sigh)

Noticed the front tires had tire shine on them, but not the back. Can only assume, they hit the curb with the front tires and used the shine to cover it up.

[4x4TX]

This is gmpartsdirect's response to me...

>No, this switch doesn't fit you truck. There are 2 choices. 1
with small
connector being 4-way, the other with smallest connector being 6-
way:
>15063844 4-way
>15067877 6-way

and then

I think we have confused you. There are two switches listed for
your truck. Since we are not able to look at the original switch
you will have to. 15063844 switch has a small connector that is
four way. 15067877 switch its smallest connector is 6 way. You
will have to determine which one you need based off the original
one in your truck. I hope this helps clarify which one you need.
If you are unsure you will need to see your local GM dealer to
make sure.

So i guess I need to verify which switch is in my truck? anyone done this themselves as far as getting to the switch and uninstalling and reinstalling it??

[battmain]

Getting to the switch is pretty easy. Set your parking brake, put your steering in the lowest position, and with the ignition on, pull the gear lever to 1. Then carefully pull the trim off around the dash. It just pops off. I started on the radio side. Once that is removed, put the gear leaver back in park and turn off the ignition. You should have access to switch at that point. Be carefull with the trim, it is huge when you try to move around to get it off. I left the passenger side door open and just set it on the seat after removing it.

[ddp127]

battmain,

That happened to me when I was driving my dad's truck once. I was sitting at a stop light and the service 4wd light came on. So I pressed 4HI. It went in to 4HI and then all the indicator lights went out. I was like, uh oh, cause I had to make a turn. I kept pressing the 2HI button, but it seemed like the switch had no power or something. I made the turn as wide as I possibly could, it was dry pavement. Soon as I made the turn I was able to get it back into 2HI.
The thing that gets me about it, is that the light only comes on when I am sitting in traffic. If I am driving on the highway it doesn't to do it. Dad and I were theorizing what it could be, we have no idea, but the switch itself could be the problem. Guess it will get looked at by the dealer, it's under warranty anyways.

Have a good one all,
Dan