2001 Chevy Blazer 4X4 problem

I am having a problem with my Blazer's 4x4. When I press the 4 hi switch the 4 hi light blinks, I hear a click from the TCCM and the 2 hi goes out. The 4 hi just keeps on blinking. When I click on the 2 hi switch the 2 hi light will blink a few times, I hear a click and it goes solid and the 4 hi light stops blinking. It does the same thing when I go from 2 hi to 4 auto but when I go from 4 auto to 2 hi the lights change but no click. I disconnected the battery for 30 min and no change. I then read on this site that you had to shift to 4 low with the vehicle in nuetral with your foot off the break so I tried that to see if the 4 low worked (previously when I tried 4 low I got the same results as the other lights). When I tried to to to 4 low this way I would hear the click of the TCCM and a loud thunk (from the transmission I guess) and the light for the 4 low would continue to blink. When I switched back to 2 hi Id get the click and the thunk again and the 2 hi light would go solid. I had a tech at the service department tell me that the TCCM may need to be replaced and maybe even the Transfer Case motor and it would cost me about $800 for both. I know I can change out the TCCM and if that would take care of the problem that would be great but I don't think I can change out the motor. Anyone have any ideas about what may be wrong. I've checked out the site but havn't found anything exactly like this one although some have been simular.

The load clunk is the transfer case being shifted by the encoder motor. You won't get a noise going to or from AUTO except for LOW range. The reason that the lights keep blinking is probably that the front axle isn't engaged. There is a vacuum solenoid on the firewall near the distributor. You might want to check if you have vacuum going into and coming out of when the switch is in 4 wheel drive. That hose goes down to the actuator under the battery tray.

Thanks for the info I'll check it out. Not to sound stupid but how do I check the vacum do I pull off the tube and stick my finger over it on both ends or what?

Thanks again

Sticking you finger over it should be OK. One side is the vacuum source, the other is the feed to the servo. The best way though is with a vacuum gage.

Ok I'll try it when it quits raining and icing here. I'll let you know what happens. Thanks for the info.

Well I tried to check the vacuum solenoid like you said. I got the hose off of the bottom of it and there was vacuum but I couldn't get the hose off of the the top. I pulled and pulled. I was afraid I would break the hose or something else if I pulled too hard. Is there a trick to get this hose off.

Just give it a gentle twist, it should come loose. If you connect both hoses together, the front axle should engage.

I have the exact problem with my 2000 Blazer. I have even check the vaccum actuator at the front axle and it seems to be working, but I still get a constant 4HI and 4LO flashing light. My problem started after replacing the upper and lower ball joints. The only thing that I might of caused my problem is that while I was working on the right ball joints the right shaft slipped out and I had a hard time getting it back in the axle. Does anyone know of something I might have done to the internal diff. that would have cause this same indication?

Thanks

On the right front output shaft of the front differential, there is a thrust washer that will drop if the axle is slid out. When that happens, the clutch sleeve can't engage the clutch gear and the front axle will no longer lock in. The tube will have to be removed to replace the thrust washer.

You are the Man! I have been looking for the problem for months, and this sounds like a winner. My plans where to drop the diff and take a look anyhow since I knew the problem must be in there, I just needed someone to give me the possible reason what might have happened. I hope the guy with his problem can be solve too. I will let you know if this works.
Thanks again.

Just give it a gentle twist, it should come loose. If you connect both hoses together, the front axle should engage.

Well I finally got a nice day and time to work on this again. I got the hose off and put the two ends together like you told me. Nothing happened. I had my wife watch the lights on the panel and the 4 hi light just kept on flashing and I didn't hear anything happen. What do I check next. Thanks.

Sometimes the vehicle has to move a couple of feet for the axle to engage (the splines of the gears have to mesh).

As long as the transfer case is shifting, the light's flashing because the front axle isn't engaged. The next move is the check the servo under the battery tray. If you have vacuum to the servo and it's not pulling back, it's a bad servo. When vacuum is applied to the servo, it should pull back the cable which engages the right side axle.

I taped the ends of hoses together and moved the Blazer a few feet and the lights stopped flashing and everything seemed to work ok. Does that mean the solenoid is bad. What does the solenoid do? Where do I find the part number for the solenoid and will it hurt to bypass the solenoid for now or should I reconnect the hoses to the solenoid?

Thanks for your help

Sometimes the vehicle has to move a couple of feet for the axle to engage (the splines of the gears have to mesh).

As long as the transfer case is shifting, the light's flashing because the front axle isn't engaged. The next move is the check the servo under the battery tray. If you have vacuum to the servo and it's not pulling back, it's a bad servo. When vacuum is applied to the servo, it should pull back the cable which engages the right side axle.

I found the number on the vacuum solenoid. It is 15706341. There is another number on it. It is 2690. I can't find the part anywhere online. Is there another number and what is the 2690 on it. Is this what is wrong?

DON'T LEAVE IT LIKE THAT. That will keep the front axle engaged at all times. It will destroy the front differential, CV joints, and tires.

Most likely, it's the solenoid. To check, hook up a test light between both wires for the solenoid. The light will go on and off with the 4X4 request.

The part number on the part isn't always the GM number, sometimes it's the casting number (subcontractor's number). The part isn't expensive.

Does anyone know the part number for the vacuum solenoid or is it called something else. I can't find it with the number thats on it or with the description "vacuum solenoid".

It's called a "Vacuum Actuator Solenoid Valve". At least, that's what it's called in the Service Manual. It might be called something else by the Parts Department.

I went to the Parts Department at my local GM dealer and they gave me the part number. It is 15165891 if anyone else needs it. He said it was called the Frount Drive Axle Actuator Valve and it cost $41.98 there. I looked on gmpartsdirect.com and found it for $23.32 before shiping and handling. It is $31.27 with shiping and handling. Havn't ordered it yet since I don't have the funds until payday. Just wanted to pass on what I found out.

It's called a "Vacuum Actuator Solenoid Valve". At least, that's what it's called in the Service Manual. It might be called something else by the Parts Department.

Thanks for all your help. I got the Vacuum Actuator Solenoid Valve today and put it on and it did the trick. Everything seems to be working fine now. You saved me loads of money. From what the Service Department said it could cost me around $800.00 for what they said was wrong and it was only a $45.00 part instead of what they said it was. Thanks again for your help ricksza.

15706341 is the old part number. Mine went bad and when I took part in to the dealer to get a new one, he cross referenced it. It cost me $47 and 4WD now works great. This is on a 2001 Blazer.

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