98 Blazer 4 door 4WD. 4WD system was making a grinding noise at during high speed deceleration and later when driving at speed. History of puking tranny fluid at the transfer case vent line. Will no longer shift into 4WD.

I have read all the threads on 4WD, but need some additional help to finish problem solving.

Vacuum switch has been replaced.
Minimal amount (drops) of tranny fluid in line to vacuum actuator. Lines have been cleaned
Definitely needs new input seal.

Can engage front axle by applying vacuum manually to actuator. No OBD-II codes.

Playing with switch got it to engage 4WD a couple of times. 15+ inches of vacuum at actuator when it worked.
Switching back to 2-HI and vacuum remained.

When I can get it to engage you can hear the encoder motor move when selecting between 4-HI and 4-Low

When not working (most of the time) cannot get vacuum at the actuator and console switch does blink 4-hi or 4-low lights on the switch when attempting to switch to 4WD.

I do not understand how the console switch causes vacuum to be applied to the actuator. I do not see where the vacuum lines go into the interior of the vehicle, unless it is the small hard line that attached to the vacuum behind/under the ABS unit.

Additional note: heater control switches DO work okay.

I suspect a faulty console switch and do not know how to diagnose.

Thanks in advance.

Kevin

More Background: 4WD fuse and Ctsy fuse are okay. Transfer case is 3 button NV233,

 

Vacuum is controlled by the vacuum switch on the transfer case which allows engine vacuum to the actuator when in 4HI or 4LO and vents the line to the actuator when in 2HI. Or that is what it should be doing. If you have vacuum to the actuator all the time, you may have connected the vacuum lines incorrectly to the switch.

The 3-button switch in the dash uses discrete contacts for each button so testing can be done easily with a multimeter set to test continuity. The schematics are posted in one or more of the NV233 related threads in the Tech Article (DIY) Index link located in my signature below. Those threads will also give you some insight into further testing that can be done.

 

Vacuum lines are connected in the same manner as when the 4WD worked. Pretty sure that is not the problem.

You said "allows engine vacuum to the actuator when in 4HI or 4LO and vents the line to the actuator when in 2HI" . How does the vacuum switch know that it is in 4HI, 4LO or 2HI. It is not electronic and I see no electronic switch anywhere in the vacuum system. This is where I am confused about the operation.

I will check electrical tomorrow, but would love to understand how the electrical switch affects the vacuum switch.

Kevin

 

The transfer case is electronically shifted. Inside the transfer case, once it shifts into 4HI or 4LO, a cam/lever pushes on the mechanical vacuum switch connecting the vacuum supply line and the line to the actuator. When electronically shifted back to 2HI, the cam/lever moves away from the vacuum switch which then closes off the connection to the vacuum supply, connecting the line to the actuator and the vent line, thereby releasing the actuator.

 

Does the cam lever mechanically move the ball at the bottom of the vacuum switch?

Is the cam mechanism activated by the encoder motor rotation?

Assuming the answer is yes to both and as noted above that when the unit is working (on rare occasion) I can hear the encoder motor moving and there are no codes set then I deduce an intermittent wiring problem or the TCCM is not recognizing that its command to position the encoder motor is failing. Is my reasoning sound?

 

Yes, as I said, when the transfer case is shifted into 4HI or 4LO, the switch is activated.

But things cannot be working properly if you still have vacuum at the actuator when in 2HI...

As far as the rest of your problem goes, testing things trumps assumptions every time. There is a lot of diagnostic information available.

 

New information. Now there is a code 2 retrieved via OBDII. I am using swartlkk diagnostic tree. Channels P,A,B,C all measure 5.01v. Not sure if in step 4 "test signal ground circuit " that means check pin 3 at connector to encode motor or somewhere else.

Any advice?

 

Looks like I need a new encoder motor. Luckily I have a working transfer case from a donor vehicle that I know was in good working order.

Can someone tell me where to split the transfer case from the transmission? There is what looks like a space between the two that I suspect is part of the transfer case and should be pulled with the transfer case. The is the part with the transmission mount on it. Does it come with the transfer case or stay with the transmission?

 

Why not just swap the encoder motors, why are you trying to remove the transfer case/

 

Leaking input seal