GGRRRR..fix one thing something else breaks ( 4x4 transfer case related)

Ok, so I over payed Uncle Sam last year and got some money back. With my last gas tank fillup I reset my trip odometer and noticed that I only got 240 miles to my tank. ( I usually get 360 before I refill) I believe my truck is getting stuck in 4x4 and is causing the unusual gas mileage.

Why do I think this?

Sometimes when I get in my truck after my wife drives it,the light on my push button 4x4 aren't lit up. I always though my wife's 3 foot long keychain was accidently hitting the button. Then I drove it for a while and it did it to me too. I would just push 2HI button and it would light up and I would drive.

This past few weeks I couldn't get the 2HI light to light up. 4HI and 4LO would light up. So I would push 2HI button anyway and I just assumed it was in 2HI but the lightbulb went out.

This week I installed a K&N air filter and a new mass air flow sensor to try to get my gas mileage back up. ( Air filter wasn't real dirty, and I had a P102 code on my code scanner, with my service engine light on) That took care of the service engine light.

I looked down and lo and behold my 2HI light was lit up. Now that I know the bulb isn't burned out, so I was thinking that the last 2 weeks my truck has been stuck in 4x4 even though the 4HI or 4LO light wasn't on. I think that since it probably was in 4x4 before ( been snowing around here) when I pushed 2HI even though 2HI wouldn't lit up, it turned off the 4HI light but didn't actually unlock the front transfer case.

Where should I start on this problem? Seems to be working now as far as I can tell. This is a 1998 Chevy K1500 Z71 4x4 with push button 4x4. Maybe the accuator? <--- might be spelled wrong. Any ideas would be appreciated.

Ok so I was driving to work today, and my truck was in 2HI on the dash. About 10 minutes down the road it was in nothing according to the dash.:banghead: So I pushed the 2HI button and it has been lit ever since.

I know think that there are 2 actuators for this 4X4 system correct? One locks the hubs in and one moves the linkage on the transfer case?

I believe one of mine is stuck. I think its the axle part because if I punch the gas in 2HI I spin in the snow. If I hit 4HI wait a few seconds and punch it, it takes off.

Gas mileage in 2HI sucks something fierce still ( 244 on this tank) and when turning or driving on pavement it just doesn't feel right. Yet when I hit 4HI and try to turn on dry pavement it will barely turn ( feels like a 4X4 on dry pavement.)

How can I test this theory out? Anyone please...I am begging.

You don't say what year. Since you have the push button 4wd system you need to find a high end scanner capable of getting into 4wd system module for codes and diagnostics.

Let us know what if any codes you come up with.

Oops forgot that part.

1998 Chevy Z71, automatic transmission, 5.7L

If I put the button in 2HI I should be able to rotate the front driveshaft correct? Then when its in 4HI I shouldn't be able to rotate the front driveshaft? ( this is assuming the truck is on the ground)

How can I check to see if the axle is locked in ? I am just about this is the problem. If I jack the frontend up,( both wheels off the ground) could I check this theory? If I spin a tire what will the other one do, assuming the axle is locked in?

Also how can I check the acuator on the front driveshaft? Voltmeter?

I am kinda confused because I heard there were 2 acuator for this 4x4. One on the transfer case by the passenger side floorboard, and one underneath the front skid plate? Also does this thing have a vacuum on it?

Would it throw and codes in the transfer case, and not show any dummy lights on the dash?

Thanks for the reply.

Would it throw and codes in the transfer case, and not show any dummy lights on the dash?

Thanks for the reply.

The lights in the dash switch are the "dummy" lights for the 4wd system. That's why I say you need a scanner capable of getting into the system for trouble shooting.

When you turn the key to the "run" position all the switch lights should blink once then come on solid for about 2 seconds and go off except for the range that is selected. That light should remain on.

With the vehicle in 2HI and all 4 wheels on the ground you should be able to turn the front drive shaft.

The usual fix for the trouble you're having is either the dash switch or the encoder-motor. That's why the scanner is essential to see if all the components are doing what they're supposed to do before you start throwing parts at it and since the lights are not working as advertised there is a good possibility that some codes are stored in the 4wd system module.