4WD Not engaging

[rudyho]

Hi,

 

I have a 98 Silverado, 160,000 miles. I just had the tranny rebuilt and for the first time when I went to push the 4 HI button it blinked and did not engage.

 

I took it back to the tranny shop and they checked out all the connections and told me it needed a electric module ($233+labor) and if that didn't fix it they would add the motor that engages the 4WD, ($333+labor).

 

When I left the shop they had it in 4HI, when I got there it was in 2 HI. I took it back and said put it in 2 HI so I can drive it until I decide what to do. He said he couldn't, and that I should just push the button enough times and sooner or later it will disengage. I laughed at him and said "according to you it needs $300 to 700 in parts before it will work, what makes think it will work now."

 

Any way, I had my friend look at it, he has had this problem with several of his trucks, and all he did was replace the Actuator ($90) in the front axle. But he was sticking a test light in a connector and I hit the button and it disengaged back into 2 HI.

 

This tells me the motor and actuator may be fine.

 

My Question is, how do I troubleshoot the actuator, electric module or motor. I need to know which part to buy and don't really want to buy one and see if it works, then buy another and see if it works.

[Bish]

Hi,

 

I have a 98 Silverado, 160,000 miles.  I just had the tranny rebuilt and for the first time when I went to push the 4 HI button it blinked and did not engage.

 

I took it back to the tranny shop and they checked out all the connections and told me it needed a electric module ($233+labor) and if that didn't fix it they would add the motor that engages the 4WD, ($333+labor).

 

When I left the shop they had it in 4HI, when I got there it was in 2 HI.  I took it back and said put it in 2 HI so I can drive it until I decide what to do.  He said he couldn't, and that I should just push the button enough times and sooner or later it will disengage.  I laughed at him and said "according to you it needs $300 to 700 in parts before it will work, what makes think it will work now."

 

Any way, I had my friend look at it, he has had this problem with several of his trucks, and all he did was replace the Actuator ($90) in the front axle.  But he was sticking a test light in a connector and I hit the button and it disengaged back into 2 HI.

 

This tells me the motor and actuator may be fine. 

 

My Question is, how do I troubleshoot the actuator, electric module or motor.  I need to know which part to buy and don't really want to buy one and see if it works, then buy another and see if it works.

 

<{POST_SNAPBACK}>

 

 

 

 

It could be the switch. My 4x4 switch went at 10K and was replaced under warranty. Similar symptom. A friend had his switch fail out of warranty and he pulled the switch, re-soldered all connections, and reinstalled it and it works fine.

 

I'm sure my Helms manual tells me what the voltage at the actuator should be. You could always hook a voltmeter up to the actuator and see what voltage you get when the pushbutton is hit. If it is getting the proper voltage, chances are it is not the switch.

 

At your mileage, I would put my money on the actuator. I think they also had both thermal and mechanical actuators and they were switched at one time for reliability reasons. Not sure which is better though.

 

Good Luck.

[99silveradoz71]

I know I had a switch failure on my 99...I know there's been a lot of talk of it here, but I believe the failures were more so on the 99+ trucks.

[Turbine Doc]

Can you go by an autozone or similar to see if they can pull a code, it is possible though; that it is stored in history section of the PCM, generally only readable with a snap on Mt2500 or GM tech 2 or equivlent.

 

Do you know anyone with either of those readers, maybe one of the pc based tools can pull up history codes, with that code & my 98 GM manual maybe we can better diagnose the problem and some test points for it, I see 9 different switches listed in the manual that could be causing the problem, a code will help pin point it.

[Jeremy WI]

Can you go by an autozone or similar to see if they can pull a code, it is possible though; that  it is stored in history section of the PCM, generally only readable with a snap on Mt2500 or GM tech 2 or equivlent.

 

Do you know anyone with either of those readers, maybe one of the pc based tools can pull up history codes, with that code & my 98 GM manual maybe we can better diagnose the problem and some test points for it, I see 9 different switches listed in the manual that could be causing the problem, a code will help pin point it.

 

<{POST_SNAPBACK}>

 

 

 

Check your service manual, you may be able to short one post at the diagnostic port to get the transfer case codes(it works on my 96). Its not the same post that the diagnostic from the PCM is.

 

In my 96 service manual, transfer case diagnostic info is in section 7D1A

[AirForceAngler]

Most likely, it is the actuator located on the front axle. These use thermal expansion to engage the front axle and were prone to failure. If you got 7 years and 160k out of yours, you're doing pretty good. Some companies make an electric/solenoid replacement that works better.

[Larry]

Hi,

 

I have a 98 Silverado, 160,000 miles.  I just had the tranny rebuilt and for the first time when I went to push the 4 HI button it blinked and did not engage.

 

I took it back to the tranny shop and they checked out all the connections and told me it needed a electric module ($233+labor) and if that didn't fix it they would add the motor that engages the 4WD, ($333+labor).

 

When I left the shop they had it in 4HI, when I got there it was in 2 HI.  I took it back and said put it in 2 HI so I can drive it until I decide what to do.  He said he couldn't, and that I should just push the button enough times and sooner or later it will disengage.  I laughed at him and said "according to you it needs $300 to 700 in parts before it will work, what makes think it will work now."

 

Any way, I had my friend look at it, he has had this problem with several of his trucks, and all he did was replace the Actuator ($90) in the front axle.  But he was sticking a test light in a connector and I hit the button and it disengaged back into 2 HI.

 

This tells me the motor and actuator may be fine. 

 

My Question is, how do I troubleshoot the actuator, electric module or motor.  I need to know which part to buy and don't really want to buy one and see if it works, then buy another and see if it works.

 

<{POST_SNAPBACK}>

 

 

 

Rudyho,

 

Although the guys above are trying to help they are mixing up different years is electronic shift 4x4 problems. I can guarantee you the problem is NOT with the front axle disconnect based on the fact the transfercase will not shift. If it would shift but still did not have 4x4 then I would suspect a front axle disconnect problem. A 1998 truck does not have a thermo actuator either. The thermo actuators went away in 1996. Yours is fully electric. (not that makes it much better). The control head (switch) problems are pretty much isolated to 1999 to current trucks with NP8 Autocrap 4wd.

 

Based on my experience working on the Chevrolet Tech Assist Hotline that supports dealer network, I would suggest first having the DTC’s read by a dealer, vautozone or somebody with a scan tool. Chances are it will have a DTC003 for an encoder motor as that is usually the failure on a 1996 through old body style 1999 truck. Don’t get excided and run out and buy an encoder motor because the transfercase control module that is located under the dash has a pretty high failure rate as well but not quite as high as the encoder motor. Either way, these two parts are relatively expensive for guesswork…..a couple hundred a piece. So, have the codes checked and follow strategy-based diagnostics first.

 

It would also be a good idea for the transmission shop to double check the wiring at the encoder motor, as they had to unplug it to remove the trans during your rebuild. Unplug the weather pack connector and make sure there isn’t any debris in the connector.

 

Electronic shifted transfercases are the absolute MOST unreliable option available on a GM truck. I have done nothing but down talk this system since it first came available in 1996. It is junk but GM is making a killing on service parts and dealers are making a killing on diagnostics, parts and labor. Do yourself a favor and do not buy this option in the future, although it is getting harder and harder to find trucks without it. Levers people, levers….why are so many people scared to buy a truck with levers????

[rudyho]

Thanks Guys,

 

I did a search or previous posts and read all about the thermal actuators and switch problems and ruled them out due to the year of my truck. I went to vautozone this morning and they didn't have any kind of equipment that would get into the transfer case history.

 

I think we have one at work in the shop. Thanks Again

 

I'll let you know what I find.

[rudyho]

I had a mechanic at work look at the problem tonight. He thinks the infamous brown wire got broke somewhere. He didn't have time to pinpoint the break in the wire since he was still on the clock at work but said it probably happened when they took my tranny out to rebuild it. There are a bunch of electrical connectors on the tranfer case and if they left one hooked up when they dropped it it could have pulled a wire off the connector pin. Of course that shop will deny it adamantly. Remember they quoted me 300-700 to fix it.

 

I also noticed a leak in the transfer case rear seal. This undoubtly came about due to the tranny shop messing with things while rebuilding it.

 

Tomorrow night he'll replace the brown wire with a new one. I'll let you know.

 

I didn't know this but he went to hook up the computer and couldn't get any reads from transfer case. That means there is a short somewhere. It was a snap-on Midox computer.

[rudyho]

FOLLOW UP

 

The transfer case wouldn't give codes to the scanning tool. Which told my mechanic the wires were messed up somewhere. He found a bad ground and the hot brown wire was loose inside a connector. The tranny shop had apparently left the connector on the T-case when they dropped it and pulled the wire and maybe the ground. He fixed the wires and got reads saying the switch was bad.

 

I thought "bad switch" that's not suppose to happen on 98's, only 99 and newer. He popped the switch out and saw it was depressed probably from me pressing a hundred times trying engage it. He pinched it, it snapped back into place and works just fine now.

 

The tranny on the other hand at 2500 miles after the rebuild started shifting really hard, I mean hard, the first time it happened I was turning a corner (right on red) and thought somebody hit me. Then it jerked again going into 3rd gear, was fine going into OD. It continued everytime going into 2 and 3rd.

 

Took it back to the tranny shop, the guy apologized and said they would fix it rght this time. I said make d**n sure the transfer case works when I pick it up, it works fine now but your guys screwed it up when they did the tranny the first time.

 

2500 miles on the second rebuild and it is going fine.