I have a 2002 Blazer, the 4wd is not working. Have replaced the dash switch, the vacuum diaphragm (actuator), under the battery tray, and the actuator cable from the actuator to the front diff, have replaced the tccm with a used one. The vacuum lines appear to be in good condition, however when my tccm was in I could hear it clicking on start up, or turning the key on. Then attempted to engage the 4x4 mode could hear the shift motor on the transfer case engage, but no shifting into 4x4. The dash light would just flash and go back to 2 hi. Any help would be appreciated. I love my Blazer 2-door.

 

Welcome to the forum!

Does the dash switch have 3 or 4 buttons?

Have you checked for manifold vacuum at the vacuum switch on the firewall with the engine running?

 

It has 4 buttons, meaning auto 4wd. Already checked the vacuum lines, checked the one at the manifold. Last night the used tccm started to work. Now the 4wd hi light flashes four or five times and then the service 4wd light comes on. The other funny thing is now the abs started working too.
Hope this info can be of some help

 

The lights are flashing a code. Count the flashes and post what you find.

Did you check for vacuum at the vacuum switch on the firewall with the engine running? In 2WD the line should not pass vacuum through the switch. When you select 4WD it should send vacuum to the actuator under the battery.

 

The 4hi light flashes 5 Times, have not rechecked the firewall vacuum switch. Tech at work is going to scan the vehicle with a scan tool to to see what codes are coming up. From doing research I'm leaning towards the shift motor on the transfer case, but not sure that's it. All the things that I have replaced more than likely needed replacement anyway.

 

Quick update on blazer. Had lead tech, who is ase certified plug scan tool in and read the code for 4wd. Code is a C0387 unable to perform shift, could this be a shift motor.

 

Could possibly be the encoder motor, (shift motor). But if you heard it shift, and then shift back to 2WD, the motor is working. It's possible the axle engagement switch on the front axle is not cancelling when the actuator diaphragm pulls in, or, the actuator under the battery tray is not working.

EDIT: If the vacuum switch on the firewall is not getting vacuum, or not switching the vacuum, the actuator will not pull in and engage the right front axle. If the axle doesn't engage, the TCCM commands the encoder motor back to 2WD and sets the C0387 in memory.

 

I heard a lot of clicking. I was under the truck today and heard the motor trying to engage, but wasn't sure it had the strength to fully engage. Its been on the truck since I've had it, I've had it since 2010, bought it with 119,000, it now has 160,000. Have not had the transfer case fuild changed yet.

 

Here's the diagnostic flow chart, not bad at all to check it:

https://blazerforum.com/forum/diagno...plained-26277/