03 GMC Sierra 4WD Not Working

barry34 · February 3, 2015

I have a 03 GMC Sierra SLT. I live in a very isolated are therefore going to my local dealer is out of the question. I am getting the dreaded Service 4WD message. If I push 4 hi, nothing happens except the light flashes When I push 4 lo, I hear the clunk, and the truck feels like it is geared down like 4 lo, but it isn't in 4wd. First thing I check was button switch, everything checked out ok. Next, I tried the encoder motor, still get Service 4wd. Next I tried the TCCM, still getting service 4WD. What else should I check (besides driving 200 miles to my dealer.) Thanks in advance, this has been a huge headache. Not to mention my fuel pump just decided to check out as well!!

durandetto · February 4, 2015

I had the same problem last year and it ended up being the actuator on the front axle. You need to get all 4 tires off the ground and put it in 4wd. If the front driveshaft is spinning, but not the front axles it's probably something to do with the axle actuator.

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gmtech4 · February 4, 2015

Scan it is the first thing to do

06pirate · February 4, 2015

I had the same issue recently on my 2006 Sierra, and it was the transfer case digesting itself internally. The oil was full of metal chunks. Hope yours isn't like that.

oldscsc · February 4, 2015

You say the truck will enter 4LO. At best, this allows you to rule out the 4WD switch, encoder motor, and transfer case. At worst, you know they aren't completely dead. Even if the front axle isn't engaging, the rest of the system is working.

If you want to throw parts at it, I would suggest the front axle actuator. This is most likely the culprit as it controls the one link in the system that is off line. Their failure isn't a rare occurrence by any means, either.

barry34 · February 7, 2015

Scan it is the first thing to do

You say the truck will enter 4LO. At best, this allows you to rule out the 4WD switch, encoder motor, and transfer case. At worst, you know they aren't completely dead. Even if the front axle isn't engaging, the rest of the system is working.

If you want to throw parts at it, I would suggest the front axle actuator. This is most likely the culprit as it controls the one link in the system that is off line. Their failure isn't a rare occurrence by any means, either.

Scanning isnt an option due to the location of the truck. I checked again today and the front driveshaft is spinning in 4Lo but not 4Hi??

gmtech4 · February 8, 2015

Scanning isnt an option due to the location of the truck. I checked again today and the front driveshaft is spinning in 4Lo but not 4Hi??

What you said makes no sense ,

It needs a tech !!!!! Stop this and take it in !!!

barry34 · February 8, 2015

What you said makes no sense ,

It needs a tech !!!!! Stop this and take it in !!!

Look, this truck is on an island which is only accessible by ferry. The ferry stopped running in November and doesnt start again until May. Like I said, scanning is not an option

oldscsc · February 9, 2015

Like I said, if I was in your situation, I'd throw a front axle actuator at it.

gmtech4 · February 9, 2015

Look, this truck is on an island which is only accessible by ferry. The ferry stopped running in November and doesnt start again until May. Like I said, scanning is not an option

Shitty, good luck