98 blazer 4wd at the end of the rope

98 Blazer 4wd-followed all the tech troubleshooting info from posts here and other places. New encoder motor, t-case vacuum switch, TCCM, and neutral safety switch. Still cannot get this vehicle to go into either 4wd hi or lo-dash switch blinks, tccm relays heard, and then back to 2wd. Nothing heard from encoder motor. So, I guess we'll change the dash pushbutton, and see what happens. I really like our Toyotas without the electronics. ANy other possible suggestions??? Thanks.

Have you checked for Diagnostic Codes?

Here is how:

1. Make sure the ignition switch is OFF
2. Under the driver's side dash, you will see a black connector pointing towards the driver seat (its the OBD-II connector), down low. In small print, locate Pin 13. It will be on the bottom row.
3. Use a wire from Pin 13 to a good ground source.
4. Turn the Ignition key to ON

What do the 4x4 lights do? If the lights blink one time and stop, there is no trouble codes stored.

If there is only 1 stored trouble codes, the code will repeatedly blink every 3 seconds. Count the number of blinks before the 3 second delay to determine the code.

If more than 1 code is stored, the first code will blink, then there will be a 3 second delay, then the next code will blink.

Once you have the codes, turn the ignition switch OFF and unhook the wire and report back here.

Have you checked for Diagnostic Codes?

Here is how:

1. Make sure the ignition switch is OFF
2. Under the driver's side dash, you will see a black connector pointing towards the driver seat (its the OBD-II connector), down low. In small print, locate Pin 13. It will be on the bottom row.
3. Use a wire from Pin 13 to a good ground source.
4. Turn the Ignition key to ON

What do the 4x4 lights do? If the lights blink one time and stop, there is no trouble codes stored.

If there is only 1 stored trouble codes, the code will repeatedly blink every 3 seconds. Count the number of blinks before the 3 second delay to determine the code.

If more than 1 code is stored, the first code will blink, then there will be a 3 second delay, then the next code will blink.

Once you have the codes, turn the ignition switch OFF and unhook the wire and report back here.
There are no stored codes.

When you first turn the ignition key to ON, do all of the lights come on and blink once?

Does the light next to the 2HI remain on (I assume that is where you're at right now).

When you press the 4HI button, does the 4HI light blink, to indicate the command was received, and it is attempting to change into 4HI?

Yes-all lights will illuminate once when the key is first turned. Yes, when either a 4 hi or 4 low selection is made, the corresponding light will illuminate, concurrent with the relay on the TCCM under the passenger kick panel making repeated contact.

We can perform this routine several times until the TCCM apparently rejects all subsequent attempts and reverts to "fail safe" allowing 2WD and rejecting any further attempts to go into either 4WD hi or lo.

I've even hooked the "old" encoder motor that is going (hopefully) to be returned for a core charge back on to the wire loom with the same results.

I see that you checked and or replaced everything BUT..... Have you checked the servo under the battery tray for tears or cracks? And have you checked that vacume line for leaks/cracks/burns?

Vacuum actuator under the battery tray is OK.

Did you do a vacume test on it? How are the hoses? And when you squeeze the vac actuator under the tray, is it pulling properly on the cable?

Issue is now resolved-bad electrical connection. Vacuum related problems are apparent when the encoder motor is able to shift and redirect engine vacuum through switch on t-case to the actuator. Thanks all for your assistance.

Hey i have the same problem but mine does everthing except disengage the front wheels. I have tested everything up and down and still have not found any mechanical defects. I have been told that it is the switch. but thats a 60 dollar maybe!!!

Ok After months of trial and error this was my problem. In the switch on the dash there are metal contacts like bridges. when a button is pushed the bridge collapses across a third contact. In my switch that bridge stuck across the 2wd contact thus never allowing the 4wd to engage. Ultimitely this burned out my tccm. With a little luck I found the switch and tccm at a local yard ( $50 for both ). Take that switch apart to see if those contacts work. The switch is a VERY simple design you should see it right away.