4 wheel drive light doesn't come on any more
- Thread starter wekelm
- Start date
Bounty__Hunter
Super Moderator
Welcome to the Z. Your 4wd light is activated by an electronic sensor on the vacuum disconnect on the passenger side of the front axle housing. You shift to 4wd and the lever mechanically engages 4wd in the transfer case. At the same time a vacuum switch mounted to the transfer case switches vacuum from one line to the front axle to another, locking the 2-piece passenger axleshaft together as one.
No dash light usually means the axleshafts are not locked together, and with the factory open front differential this means the front tires will not have power when in 4wd. A good test is to try to spin the front tires in 4wd when in loose gravel or snow. Have somebody watch from outside the vehicle.
To diagnose the front axle disconnect, remove the two vacuum lines from the passenger side of the front axle housing. Have the Jeep running and the tires safely chocked, have somebody shift from 2wd to 4wd and back to 2wd. You should have strong vacuum alternating between the two vacuum lines depending on 2wd or 4wd.
If you have weak vacuum, you either have a broken vacuum line in the system or a bad vacuum switch on the transfer case.
Strong vacuum, your next step is to remove the vacuum disconnect from the axle housing. Simply attached with 4 bolts. Minimal gear oil will leak out, no worries. With the vacuum lines removed, manually move the aluminum shift fork. It should move easily and air should exit one of the vacuum ports. Water will come out if you have water in the system. These shift forks occasionally seize and the entire disconnect assembly needs replaced.
Let us know what you find. It's really a simply system to work on once you know how it works.
As far as vacuum lines in the axle disconnect system, you have a red line from the intake manifold to the vacuum switch on the transfer case. You have a blue vent line from beneath the battery to the vacuum switch. You have two black lines along the passenger frame rail from the vacuum switch to the front axle. That's it, simple. The lines passing beneath the battery often corrode, good spot to check.
No dash light usually means the axleshafts are not locked together, and with the factory open front differential this means the front tires will not have power when in 4wd. A good test is to try to spin the front tires in 4wd when in loose gravel or snow. Have somebody watch from outside the vehicle.
To diagnose the front axle disconnect, remove the two vacuum lines from the passenger side of the front axle housing. Have the Jeep running and the tires safely chocked, have somebody shift from 2wd to 4wd and back to 2wd. You should have strong vacuum alternating between the two vacuum lines depending on 2wd or 4wd.
If you have weak vacuum, you either have a broken vacuum line in the system or a bad vacuum switch on the transfer case.
Strong vacuum, your next step is to remove the vacuum disconnect from the axle housing. Simply attached with 4 bolts. Minimal gear oil will leak out, no worries. With the vacuum lines removed, manually move the aluminum shift fork. It should move easily and air should exit one of the vacuum ports. Water will come out if you have water in the system. These shift forks occasionally seize and the entire disconnect assembly needs replaced.
Let us know what you find. It's really a simply system to work on once you know how it works.
As far as vacuum lines in the axle disconnect system, you have a red line from the intake manifold to the vacuum switch on the transfer case. You have a blue vent line from beneath the battery to the vacuum switch. You have two black lines along the passenger frame rail from the vacuum switch to the front axle. That's it, simple. The lines passing beneath the battery often corrode, good spot to check.
Bounty__Hunter
Super Moderator
Glad you found it, your welcome.
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