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Mazda Ed
Mazda Ed, Auto Service Technician
Category: Chevy
Satisfied Customers: 2223
Experience:  ASE Master Technician, Mazda Master Technician, GM and Ford factory trained. 15 years experience.
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1998 Chevy Blazer: the 4WD wont engage..vacuum line..whats wrong

Customer Question

Hello, I have a 1998 Chevy Blazer, and the 4WD won't engage. My boyfriend has a blazer and so does my neighbor and they both have had same problem. My neighbors problem was solved by getting a new vacuum line, but that isn't whats wrong with mine. Is this something that is really common with Blazers? And if so, what else could it be? (By the way, we just realized that my 4 low DOES engage, but when we push the 4 high button it blinks and then goes back to 2 high). I hope you can help! You were extremely helpful before! Thank you!
Submitted: 8 years ago.
Category: Chevy
Expert:  Mazda Ed replied 8 years ago.


I just got done helping another customer a couple of days ago with the same exact problem. Since you removed the battery, the module should have already reset. If for some reason it did not, then remove the connectors from the TCCM. It is located behind the kick panel on the passenger side. Check the connectors for signs of water. If your boyfriends blazer has the same TCCM then you can try swapping his in temporarily. If it is different, then reconnect the TCCM after several minutes and try all mode shifts. Let me know which shifts are working and which are not.

2HI -> 4HI

4HI -> 4LO

2HI -> 4LO

4LO -> 2HI

4LO -> 4HI

4HI -> 2HI

Customer: replied 8 years ago.
Hi, I did receive your answer, but haven't yet been able to try your suggestion. It has been raining really badly here. I promise to get back to you just as soon as I can work outside. Thanks so much. Jess
Customer: replied 8 years ago.
Expert:  Mazda Ed replied 8 years ago.
The 95 uses a different system than the 98 so that won't help you out. Let me know when you do the testing from above.

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