Will not shift the front wheels into 4X4

GTC5616

MEMBER
1998 CHEVROLET BLAZER
6 CYL
4WD
AUTOMATIC
180,500 MILES

Hello, my 1998 chevy blazer LS with an electronic 4x4 shift will not shift the front wheels into 4x4. The truck shifts into low gear and you can feel the difference, but the front wheels do not go into 4x4 HI or LO. I know it is a solenoid problem, but I not sure which one I need. The vacuum device under the battery box, or the solenoid on the front gear housing? I need some help diagnosing it so I don't end up buying parts that don't need replacing.

5 Replies

HMAC300

MECHANIC
48,601 POSTS

Get a hleper and a test light. Have the helper turn the key on and move the switch on the dash hi to lo, etc. And put your test light on the disconnected electrical connector and see if it's getting power. If it is then see if you can feel it working. This could be a module that is screwing up as well. That is in the kick panel on the passenger side. But be forewarned you will probably have to have it reprogrammed if the module is bad.

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Friday, May 14th, 2021 AT 12:30 PM

GTC5616

MEMBER
13 POSTS

So it is getting signal. There is a pump under the battery and a solenoid that goes into the side of the front differential which the cable goes to from the pump under the battery. Is it both of these that are bad, or just one? Which one should I test and how? Would it have anything to do with the vacuum on the transfer case in the rear?

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Friday, May 14th, 2021 AT 12:30 PM

HMAC300

MECHANIC
48,601 POSTS

If the solenoid on the axle is getting power and it doesn't engage, then'i'd have to say it's a solenoid. You should be able to feel it working if it's getting power. Or hear it moving. As I can't check it myself and am going by what you say. If youi take teh solenoid off and hook it up you should see it work by using the switch.

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Friday, May 14th, 2021 AT 12:30 PM

GTC5616

MEMBER
13 POSTS

I can hear it click in, today I replaced to actuator on the transfer case and the actuator vacuum pump under the battery, and it still doesnt work. I tried doing some vacuum tests and I know the pump under the battery gets vacuum from the actuator, but I am not sure if it is getting anything to the actuator? The pump and the actuator had oil in the lines which mad me believe the actuator on the transfer case wasnt working properly. I am not sure where to go from here, aside form replacing all the vacuum lines. I can hear the solenoid working and click in and out of the gears when I shift through them.

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Friday, May 14th, 2021 AT 12:30 PM

HMAC300

MECHANIC
48,601 POSTS

If you can hear the solenoid working take it out and see if it actually does or not. I thought i sent this diagram before but i guess not . I cannot find the vacuum pump/ tank you keep talking about though.