98 Jimmy stuck in 4WD - Can't go to 2HI

I think I've read all the relevant post on this topic but still uncertain as to what my solution may be.

It's a 98 Jimmy with 3 button system. If it's in 2HI, it shifts perfectly to 4HI. I can then shift to 4LO, and back again to 4HI. But it does not then shift back to 2HI. Eventually, after rocking the truck and pressing the 2HI button, it will shift back. Sometimes takes 10+ minutes of trying. So you can imagine, I hate to use the 4WD, but sometimes need it.

Here's the thing. I can hear the TC shifting as I press the button, but then appears to shift back again and end up staying in 4HI. I read a post about the encoder motor on the TC being bad. But it shift fine between Hi and Lo. Is there really a "shift" involved between 4HI and 2HI? Is this shift really one to change the vacuum position, to de-activate the vacuum to the front diaphram up front?

I jacked up the front end of the truck when it was stuck in 4wd and with the engine off, I am able to spin the front wheel. Started the truck up, vacuum was applied and the wheel would no longer spin.

I've been trying to figure out what's wrong with this for a long time. The dealer said they'd recommend replacing everything in the system. About $1800. No way I'm spending that. Thanks for any advise you may have.

First thing check fluid level in transfer case.

Do not operate it in 4W on dry payment.
Normal driving or normal 4W you do not need 4W low.

Is your tires a matched set?

First try backing up shift to neutral and let it roll forward.
If that helps it may be just binding up from driving on dry payment.
Post back if that helps.

Fluid level is ok. Yup, I don't drive it on dry pavement. But people must think I'm nuts because I drive in the snow covered edge of the road instead of the dry track marks when its suck in 4wd.

I've tried all methods of shifting it. My driveway is shaded so always stays snow covered. I try backing up, then rolling forward as you suggested, rolling forward and turning left or right, etc. Nothing.

But since I'm in 4HI, the does the transfer case even need to shift to go to 2HI. The front drive axle always is engaged, correct? Then it's just a matter of the front axle being engaged or disengaged.

Is it the transfer case encoder motor that controls the vacuum to the front axle?

Thanks.

The encoder motor shifts transfer case in and out of 4W
Vacuum is seperate from encoder motor.

In 4W the front drive shaft is engauged.

On yours if it does not shift out of 4W to 2W or show 2W on lights check transfer case and front drive shaft for locking in and out.

http://www.automotiveforums.com/vbulletin/showthread.php?t=572914

Check for codes on yours by grounding pin 13 on diagnostic connecter and watching the shift button lights.
Post back codes/button flashes.

Ok, I'm still confused.

The link in the previous post indicates that the front drive shaft is always active, 4WD or 2WD. So the transfer case is always engaged, either in High or Lo. So it seems the only different between 4HI and 2HI is that vacuum is supplied to the diaphram under the battery, which in turns pulls the cable to the front axle and engages 4WD.

This is indeed what I find on my vehicle. It is stuck in 4HI, but when the engine is off, the front axle is not engage due to a lack of vacuum being supplied.

So I think my question is this: What happens when you shift from 4HI to 4 LO that signals the vacuum to NOT be supplied to the front axle?

From 4W high to 4W low the front axel and vacuum to should remain the same or locked in.
If shifted to 2W the vacuum switch on transfer case should shut off vacuum to front axel
The gear ration in trasfer case from high to low 4W is the only thing that should change on 4W High to 4WLow
The encoder motor moves the transfer case from 4Wh to 4WL position.
Giving you a low gear ratio.

Stupid typo in my last post.

The question I was trying to ask is:

What happens when you shift from 4HI to 2WD that signals the vacuum to NOT be supplied to the front axle?

The vacuum switch on the transfer case controls engine vacuum to front axel

So I just checked the TC fluid level. It's right where it should be.
And I can see the front axle vacuum actuator under the battery tray pull the cable out as I start the vehicle, and it releases when I turn the vehicle off, and vacuum goes away.

Any other ideas?

Did you check for codes?
Make sure the transfer case encoder motor is shifting from 4W to 2W.

A facory repair manual or.
http://www.alldata.com/products/diy/index.html

Will explain what is what,

So are you saying the TC does shift from 4H to 2H? By shift do you mean actually engage gears, because I believe the front shaft is engage in 2H the same as it is in 4H?

Or is there some sort of shift in the transfer case refering to a position that signals the vacuum to no longer be applied to the front axle actuator, when in the 4W positions (4H and 4LO)

Checko for codes and post back codes.

In 4WH and 4WL the front axel should have vacuum and be be engauged.

If transfer case is shifting to 2W there is a vacuum switch on the transfer case that should shut off vacuum to front axel and the transfer case computer will turn off all electrical circuits for 4W.
In 2W the 2W button should light up and stay on.
Does yours do that?

Let me ask another question.

All electronics and sensors aside, is being in 4HI with out the front axle being engaged, the same as being in 2HI?

If so, I can just unhook the actuator under the battery and safely drive the truck, even with the switch inside reading 4HI

Let me ask another question.

All electronics and sensors aside, is being in 4HI with out the front axle being engaged, the same as being in 2HI?

If so, I can just unhook the actuator under the battery and safely drive the truck, even with the switch inside reading 4HI


It is always best to fix it right.

HELP! I am having the EXACT SAME ISSUE! I could swear I could have wrote the description to the problem!

This is my First 4x4 vehicle and I don't know too much about it.

The one thing that worried me about what i've read is, "Don't drive on dry pavement in 4W?" why not? I've never been told anything about this... I don't make it a habit to drive on dry pavement in 4W as it is quite un-necessary, but it happens when there is a part of the road that is dry, or plowed well... what can that do to the truck?

How did loots42 fix his truck?!

Please Help.

Well, I'm not sure I fixed the problem, but I got it back in 2HI, I put the truck in 4LO, and drove out of my parking lot to the street which is sloped, then I drove the truck in reverse at about 15-20 km/h to the top of the hill, then popped the truck into neutral and as it was rolling back down the hill press the 2HI button and it shifted right away.....

Found a solution, but don't know why.

HELP! I am having the EXACT SAME ISSUE! I could swear I could have wrote the description to the problem!

This is my First 4x4 vehicle and I don't know too much about it.

The one thing that worried me about what i've read is, "Don't drive on dry pavement in 4W?" why not? I've never been told anything about this... I don't make it a habit to drive on dry pavement in 4W as it is quite un-necessary, but it happens when there is a part of the road that is dry, or plowed well... what can that do to the truck?

How did loots42 fix his truck?!

Please Help.

Loots did not say.:lol:

Best to start your own New -Thread.
Saves on hy jacking someone else's thread.
Give all info on your truck and problem and what transfer case you have.
And someone will help you.

I believe its the transfer case shift motor (encoder). I hear it trying to shift from 4 to 2 (although I'm still not sure from the discussions I've read nor this thread that there is actually a mechanical shift of disengaging the gears in the transfer case when you shift from 4HI to 2HI).

So my problem is not fixed yet.

I took the shift motor off today. I supported it with the wires still attached. The truck was in 4LO wen I took the motor off. As I press the shift button to 4H, I can see it turn from the lo possition to the high position. And then when I press the 2HI, it shifts in the exact same manner as when selecting 4HI. What it does is tries the shift twice. Since It isn't actually hooked up to the Transfer Case, it defaults back to 4LO.

So can I conclude it's not the transfer case motor? Any other ideas for this problem?

I took the shift motor off today. I supported it with the wires still attached. The truck was in 4LO wen I took the motor off. As I press the shift button to 4H, I can see it turn from the lo possition to the high position. And then when I press the 2HI, it shifts in the exact same manner as when selecting 4HI. What it does is tries the shift twice. Since It isn't actually hooked up to the Transfer Case, it defaults back to 4LO.

So can I conclude it's not the transfer case motor? Any other ideas for this problem?


Proper testing will give you the answer.

Check for codes.
Get the all data sub to guide you along.
AND HELP YOU OUT.
http://www.alldata.com/products/diy/index.html

GOOD LUCK

Hello - I hope this helps:

I drive a 99 Blazer. I have the exact same problem, but here is what I discovered that seems to solve the problem: Let the truck sit in neutral before going back to 2HI. I can shift into either 4WD ranges fine sitting at a complete stop in park or drive, but the only way I can get back to 2HI is by going back to neutral first. I don't know if it is supposed to be like this as the push button 4WD system is quite different than what I had on my 83 CJ7!

Good Luck!

Hello - I hope this helps:

I drive a 99 Blazer. I have the exact same problem, but here is what I discovered that seems to solve the problem: Let the truck sit in neutral before going back to 2HI. I can shift into either 4WD ranges fine sitting at a complete stop in park or drive, but the only way I can get back to 2HI is by going back to neutral first. I don't know if it is supposed to be like this as the push button 4WD system is quite different than what I had on my 83 CJ7!

Good Luck!

Good suggestion. 99BlueBlazer
Yes that is normal.
Tires not matched or operating in 4W on dry payment adds to the problem of shifting back out of 4W.
On Some it also helps to back up or let it roll back some.

When I had the TC shift motor off, I put an open end wrench on and was able to shift to 3 distinct positions just fine and easily using the 14mm wrench. So I'm pretty sure at this point that it's not a mechanical problem of binding with the TC.

I put it back on and it still only shifts between 4LO and 4HI, but not to 2H. After trying to shift about 50 times, it'll then shift to 2H.

MT-2500 - the 4wd light is not on. The Chilton manual I have say I must have a OBDII scan tool (I know the cheap ones won't read tc codes), and does not outline the procedure manual procedure to ground the test terminals to get flash codes. Is there another way to get the codes?

When I had the TC shift motor off, I put an open end wrench on and was able to shift to 3 distinct positions just fine and easily using the 14mm wrench. So I'm pretty sure at this point that it's not a mechanical problem of binding with the TC.

I put it back on and it still only shifts between 4LO and 4HI, but not to 2H. After trying to shift about 50 times, it'll then shift to 2H.

MT-2500 - the 4wd light is not on. The Chilton manual I have say I must have a OBDII scan tool (I know the cheap ones won't read tc codes), and does not outline the procedure manual procedure to ground the test terminals to get flash codes. Is there another way to get the codes?


Go back and read post no 4.

When you get codes post back code no.

For good repair info.

http://www.alldata.com/products/diy/index.html

I grounded terminal 13 and it reported no codes. The truck is currently in 2HI, and when I ground 13 and turn the ignition on, no lights blink on the 4wd switch. So no codes. Hmm.

HELP! I am having the EXACT SAME ISSUE! I could swear I could have wrote the description to the problem!

This is my First 4x4 vehicle and I don't know too much about it.

The one thing that worried me about what i've read is, "Don't drive on dry pavement in 4W?" why not? I've never been told anything about this... I don't make it a habit to drive on dry pavement in 4W as it is quite un-necessary, but it happens when there is a part of the road that is dry, or plowed well... what can that do to the truck?

How did loots42 fix his truck?!

Please Help.

It sounds to me that a good start would be replacing the vacuum switch on the transfer case.

I grounded terminal 13 and it reported no codes. The truck is currently in 2HI, and when I ground 13 and turn the ignition on, no lights blink on the 4wd switch. So no codes. Hmm.

Are you sure you grounded pin 13?
With pin grounded.
Do they all come on and go off for the key on bulb check?

With pin 13 grounded do they all come on and go off for the bulb check?

I'm pretty sure. Count 1-8 on top row, and start with 9 on lower row on the left. I had a thin piece of wire that I shoved into the pin 13 terminal, and then grounded the other end to the emergency brake bracket. If I ungrounded it, the lights lit up as usual. When I grounded it, no lights on the 4wd switch light up.

I'm pretty sure. Count 1-8 on top row, and start with 9 on lower row on the left. I had a thin piece of wire that I shoved into the pin 13 terminal, and then grounded the other end to the emergency brake bracket. If I ungrounded it, the lights lit up as usual. When I grounded it, no lights on the 4wd switch light up.

Do all 4W lights come on for a bulb check when key is turned on and then go off?

Without grounding pin 13, yes

Without grounding pin 13, yes

Yes
And the try it grounding pin 13.
http://www.troublecodes.net/OBD2/

With grounding 13, no lights on the 4WD selector illuminator, nor blink

With grounding 13, not lights on the 4WD selector illuminator, nor blink


What do they do if you do not ground it?
Does all button lights come on for a bulb check and the go out when key is turned on?

Yes, when I turn it on, all lights, dash and 4wd selector go on. Then when I start it up, the dash lights go off, and the proper 4wd switch light is illuminated.

Yes, when I turn it on, all lights, dash and 4wd selector go on. Then when I start it up, the dash lights go off, and the proper 4wd switch light is illuminated.

The key question is
Does all 4W buttons light up for the key on bulb check and then go out and then show you what gear it is in?

You need to get some good repair info on it like a factory repair manual or the all data on line sub for one year one car sub. about 26.95$ usa plastic.
http://www.alldata.com/products/diy/index.html

The all data on line sub will take you step by step threw the testing process.
Good luck

Yes, all the 3 lights (2H,4H4L) light up momentarily, then 2 of the 3 go out. It is left showing which range the truck is in.

Yes, all the 3 lights (2H,4H4L) light up momentarily, then 2 of the 3 go out. It is left showing which range the truck is in.

Ok.
If the lights do not come on for bulb check with pin 13 grounded.
You need to get the All Data sub and go threw the repair flow chart for that problem.
It will led you threw the repair step by step.
Good Luck

Ok, after grounding pin 13, all lights go on momentarily, then go out and none come back on. So no code is thrown.

I did discover that when stuck in 4wd, if I repeatedly, and quickly shift back and forth from 4Hi to 4Lo, it will jump into 2H.

I subscribed to alldata.com. It did not have a use case for the problem I had.

I suspected it was the encoder motor, but started with the TCCM from a junkyard for $50. That wasn't it. So I bought a rebuilt encoder motor ($125)and now if shifts beautifully.

I subscribed to alldata.com. It did not have a use case for the problem I had.

I suspected it was the encoder motor, but started with the TCCM from a junkyard for $50. That wasn't it. So I bought a rebuilt encoder motor ($125)and now if shifts beautifully.

Thanks for posting back the fix.
Glad you got it fixed.

The All data should have all of the repair flow charts and test for it.
It is the same as factory repair manual.
But sometimes the info is hard to find in there.
If you can not find the info contact all data and they will help you find it or send the info to you.
They are very good at helping you.

Good Luck