'98 4x4 locked in (again)

Backing out of our driveway, the electronic 4x4 went from 2hi to 4hi on it's own. This has happened several times before but have been able to get back into 2hi by pushing buttons, fiddling and whatever.
This time it is stuck in 4hi and no amount of button pushing or backing up or(?) will resolve it.
It shifts easily into 4lo with no problem. When 2hi is pressed, it shifts to 4hi and that is it.
I have confirmed that the transfer case is in 4wd since the driveshaft to the front axle turns when driven and will not turn freely by hand when the engine is off.
When the 2hi button is pushed, there is the clicking sound from behind the glove compartment and also the sound of the transfer case motor running. The 2hi button flashes while this is happening but the end result is 4hi being lit.
The battery has been disconnected multiple times with no resetting of the system. No fuses can be found that are blown and all systems appear to be operating except for going into 2hi.
I grounded pin 13 and found no error codes. It is not a vacuum problem since the actuator engages properly. Also, the transfer case motor and the transfer case control module were replaced 8mos/4000mi ago and the fluid changed.
In order to drive it, I have removed the vacuum line to the actuator and plugged it.
Help! What is my next step??? Any ideas would be much appreciated!

If you clear the codes by removing fuses or disconnecting the battery, it still sets DTC 1 in the system. The system won't work if it's there. This code is cleared by cycling the ignition switch from the OFF position to the RUN and back OFF five times in order to clear DTC 1 from the transfer case shift control module memory

Remove the negative battery terminal from the battery for 10-15 minutes and try again.

You might have logic lock.

Clearing the computer will sometimes fix it.

Backing out of our driveway, the electronic 4x4 went from 2hi to 4hi on it's own. This has happened several times before but have been able to get back into 2hi by pushing buttons, fiddling and whatever.
This time it is stuck in 4hi and no amount of button pushing or backing up or(?) will resolve it.
It shifts easily into 4lo with no problem. When 2hi is pressed, it shifts to 4hi and that is it.

I have confirmed that the transfer case is in 4wd since the driveshaft to the front axle turns when driven and will not turn freely by hand when the engine is off.
When the 2hi button is pushed, there is the clicking sound from behind the glove compartment and also the sound of the transfer case motor running. The 2hi button flashes while this is happening but the end result is 4hi being lit.
The battery has been disconnected multiple times with no resetting of the system. No fuses can be found that are blown and all systems appear to be operating except for going into 2hi.
I grounded pin 13 and found no error codes. It is not a vacuum problem since the actuator engages properly. Also, the transfer case motor and the transfer case control module were replaced 8mos/4000mi ago and the fluid changed.
In order to drive it, I have removed the vacuum line to the actuator and plugged it.
Help! What is my next step??? Any ideas would be much appreciated!

I have a 1999 and when I put it 4Lo, even if I push 2hi, it goes to 4hi. I don't think you can take it from 4lo directly to 2hi....think it has to stop at 4hi then you can move it to 2hi

I appreciate the input. I cycled the ignition on/off 5 times and there was no change. I disconnected the battery(again) for 20 minutes and no change. I tried cycling the ignition on/off 5 times again and no change.

I do not only try to go directly from 4lo to 2hi - trying to go from 4hi to 2hi has the same result - stuck in 4hi......

I appreciate the input. I cycled the ignition on/off 5 times and there was no change. I disconnected the battery(again) for 20 minutes and no change. I tried cycling the ignition on/off 5 times again and no change.

I do not only try to go directly from 4lo to 2hi - trying to go from 4hi to 2hi has the same result - stuck in 4hi......

Time to check the vacuum actuator and the transfer case encoder motor.

I also have a 98 Blazer. It went into 4wd on its own a couple times. The last time it did it I had a hard time getting it out but finally it went out on it's own. I hadn't used it for several months after that. When I went to use it nothing worked. I get several clicks from the module then nothing. I tried replacing the TCC module and encoder motor from wrecking yards with no success. Not sure what to do at this point.

Your module may not be working any more and not able to send a signal to the encorder motor. Or the encoder motor may be burned out and not able to shift out of 4wd. You may have to remove the encoder motor and manually turn the connection to get it out of 4wd. Then you will still be stuck trying to track down the cause, but you will at least be able to drive it without 4wd.

I'm still researching mine and as I learn more I will update you. All I know is this is too complicated of a system. Dealers will only start replacing parts at several hundred each until they either find it or give up and leave you where you were to start just severl hundred less money in your pocket.

Time to check the vacuum actuator and the transfer case encoder motor.

As stated in my original post, the vacuum actuator works properly and engages the front axle. I have disconnected the vacuum line to it and plugged it so that it can be driven.

If it shifts back and forth between 4hi and 4lo with no hesitation or problem, doesn't that mean the encoder motor is working properly?

I appreciate any help I can get. This 4x4 system is mind-boggling!!!

I also have a 98 Blazer. It went into 4wd on its own a couple times. The last time it did it I had a hard time getting it out but finally it went out on it's own. I hadn't used it for several months after that. When I went to use it nothing worked. I get several clicks from the module then nothing. I tried replacing the TCC module and encoder motor from wrecking yards with no success. Not sure what to do at this point.

Your module may not be working any more and not able to send a signal to the encorder motor. Or the encoder motor may be burned out and not able to shift out of 4wd. You may have to remove the encoder motor and manually turn the connection to get it out of 4wd. Then you will still be stuck trying to track down the cause, but you will at least be able to drive it without 4wd.

I'm still researching mine and as I learn more I will update you. All I know is this is too complicated of a system. Dealers will only start replacing parts at several hundred each until they either find it or give up and leave you where you were to start just severl hundred less money in your pocket.
I appreciate your input. How hard is it to remove the motor and get it out of 4wd? I saw in another thread that you use a 5/8" wrench to get it out of 4wd after removing the motor. If and when I resolve this, I will let you know the cure! May just have to write a book on the subject - or is there one?

I appreciate your input. How hard is it to remove the motor and get it out of 4wd? I saw in another thread that you use a 5/8" wrench to get it out of 4wd after removing the motor. If and when I resolve this, I will let you know the cure! May just have to write a book on the subject - or is there one?


To remove the encoder motor, first you will have to remove the front drive shaft. Then remove the harness off the encoder (8mm socket). Then unbolt the encoder motor (10mm socket). Once it's off, turn the shaft with a 5/8 open end wrench to shift.

To remove the encoder motor, first you will have to remove the front drive shaft. Then remove the harness off the encoder (8mm socket). Then unbolt the encoder motor (10mm socket). Once it's off, turn the shaft with a 5/8 open end wrench to shift.

Thanks for the detailed info - it is much appreciated.
I have disconnected the vacuum actuator so the front axle does not lock in but the transfer case is still in 4hi and the front drive shaft is still turning. Will this do any damage to the drivetrain? Should I remove the front drive shaft to prevent any damage? Or??? I live in Florida and really do not need 4wd since I do not offroad......

If the front differential is deactivated but the transfer case is still 4X4, probably the only thing you will notice is a drop in gas milage. There is the additional wear on parts to consider. I would remove the front driveshaft, less moving parts is always better.

One other thing to consider, if the vehicle thinks that it's in 4X4, some ABS functions won't work.

If the front differential is deactivated but the transfer case is still 4X4, probably the only thing you will notice is a drop in gas milage. There is the additional wear on parts to consider. I would remove the front driveshaft, less moving parts is always better.

One other thing to consider, if the vehicle thinks that it's in 4X4, some ABS functions won't work.

Once again, thanks to everyone for the help.

I have not given up on this mystery but am not yet ready to subject myself to the "Remove & Replace 'til it works" folks...

Since this problem first began I have been pushing the 2hi button on occasion. Today I pushed it and it went into 2hi!!! I couldn't believe it so I cycled it through 4lo and pushed 2hi and it went back into 2hi!!! Unfortunately I could not let well enough alone and tried it again - back to the same old problem - stuck in 4hi....

Maybe the 2hi GOD will look down on me again and shift for me!!!!!!!!!

I appreciate your input. How hard is it to remove the motor and get it out of 4wd? I saw in another thread that you use a 5/8" wrench to get it out of 4wd after removing the motor. If and when I resolve this, I will let you know the cure! May just have to write a book on the subject - or is there one?

I finally got a chance to do some work on my Blazer. My son has a friend with a 2000 Blazer, so I plugged my module and encoder motor into his Blazer. Both my parts worked fine on his car. The dealer is the one that did the diagnostic test on my car and told me that one of these two parts were bad. My guess now is that the problem is in the switch. I am going to replace it and see what happens.

I finally got a chance to do some work on my Blazer. My son has a friend with a 2000 Blazer, so I plugged my module and encoder motor into his Blazer. Both my parts worked fine on his car. The dealer is the one that did the diagnostic test on my car and told me that one of these two parts were bad. My guess now is that the problem is in the switch. I am going to replace it and see what happens.

Appreciate your staying in touch. I haven't had any success in getting it out of 4hi. It hasn't "volunteered" to do it by itself and pushing the button hasn't worked since. I have not disconnected the front drive shaft yet but have released the vacuum actuator so the front axle acts as if in 2hi.
If I discover any miracle cure, I'll let you know. Stay in touch...