4x4 system online, but not engaging
 

Hi all,

I have a 2000 LS Blazer, 4WD. Over the summer, noticed a strange noise while on the highway, I would describe it as the noise you get when you stick playing cards in bicycle spokes. Did some digging and eventually brought it to the shop, they told me that it was most likely a bad actuator, and the noise was caused by the 4WD engaging and disengaging rapidly...anyone else have this problem? Vacuum solenoid and the actual module by passenger side footwell were serviced a couple years back so I don't think it's anything there. Looking to get the 4WD back and working before the snow sets in.

Thanks

Do you know if the transfer case is engaging? You should be able to hear it.

Is the TCCM (transfer case control module, under the passenger side kick panel) clicking a lot? It should not be. When you press the 4wd button the reed relays should click once. If they click many times, the unit is failing. Sometimes the issue can be due to corrosion on the electrical connectors to the TCCM.

Are your vacuum hoses under the hood not leaking? They tend to rot after they get to the 15 year mark depriving vacuum to the actuators for both the HVAC and the front axle engagement actuator. They can look good visually but still be leaking.

If all of the above are working as they should, the engagement gear at the front axle can be bad or worn. This might have been the origin of the noise you described. If so, the front axle would have to be serviced. (part number 8 in the exploded parts diagram: https://www.gmpartsnow.com/v-2000-ch...fts-and-joints)

I'm sure others will be able to suggest some other things to check.

Check the front axle actuator by jacking up the passenger front wheel. With the engine started and in 4WD, can you turn the wheel by hand?