Jeep Wrangler Four-Wheel Drive Won’t Engage

Assure the safety standards of your vehicle

You never know when you may encounter a slippery road. It is best to be prepared. That’s why it is important to assure that your four-wheel drive is working at all times. You wouldn’t want to lose control over your Wrangler if it rains or the forthcoming road is slippery. A small moment of imbalance and lost control could lead to unimaginable expenses on repairs, and maybe an injury that leaves a mark. 

It is very important to maintain this aspect of your Wrangler. If your Jeep Wrangler four-wheel drive won’t engage, it is recommended that you take it to a mechanic as soon as possible. Know that your Jeep only utilizes front-wheel-drive while normally driving down the road. But uncertain conditions demand exceptional balance for which the other wheels must also gain traction. While this may reduce your fuel-economy, it is anyhow an essential feature to rely on in the colder months. 

Check whether your four-wheel drive is working 

There are several methods to check whether your four-wheel drive is working. The easiest way is to remove traction from your wheels and let them all spin at the same time. 

The commonest method of assessing a four-wheel drive is by lifting the Jeep off the ground. This may require some specific ability and some standard tools but this method lets you clearly analyze the position of your Jeep’s 4WD. If all the tires spin and try to find traction when you press your foot on the gas, your four-wheel drive is perfect.

Another common method utilizes help from a tree. You need to drive your Jeep in such a way that the front portion is touching the tree. You can call help who’ll note whether all the wheels spin when you drive your Jeep against the tree. However, you must not hit the tree very hard or your car could get damaged. If all your wheels engage in your attempt against the tree, your four-wheel drive is perfectly fine. 

Know why your four wheel drive may not be working 

There could be several valid reasons behind the failure of your four-wheel drive. There could be a failed actuator or the vacuum hose could have incurred some damage. It is also possible that your vacuum hose may be unhooked. In many cases, the vacuum switch turns out to be at fault. 

Your actuator may have failed 

It is possible that your Jeep’s actuator may have failed. An actuator is an essential component, typically found in four-wheel drives. The function of this part is to electrically engage the four-wheel drive. This is accomplished with the help of a small electric motor that is bolted on the transfer case. This helps in shifting a pin to its proper place to skillfully lock the center transfer differential. 

The actuator lets you shift from a two-wheel to a four-wheel drive. Also, you can shift back to a two-wheel-drive whenever you please. The engagement and the disengagement are accomplished by the means of a switch upon the dashboard. The electrical activation of the actuator is done with the help of an air vacuum system. This reliable device is so efficient that you don’t even need to stop the Jeep or get out to engage the four wheels during the drive. 

It is possible that the internal gears inside the actuator electronic module or the motor may have failed. 

Your vacuum hose could have been damaged

YJ Jeep Wranglers could incur a failure in the automatic vacuum system that helps in locking and unlocking the hubs when engaging and disengaging a four-wheel drive. It is also possible for vacuum hoses to not function properly in engaging the four-wheel drive if the vacuum pressure is insufficient and does not reach up to the front axle shift motor. 

All the hoses will need to be traced to ensure that they are working correctly. If there was an air pressure gauge right before the front axle input, it would be relatively easy to know whether all of them are functional. Any air leak in the pipelines would also be easily detected. Although, you can easily check the functioning of the hose by placing a flexible pipe to your ear and running it all along the hose to check for leaks. If the hoses are damaged, air would leak when you engage the four-wheel drive.

One simple way to get over these frequent vacuum leaks is by upgrading to a 4×4 Posi-Lock system. It is easy to accomplish on your own and you’ll never have to worry about a leak or a non-engaging four-wheel drive again.

Your vacuum hoses could be ripped 

Any failure in the vacuum system will make it difficult for you to engage the four-wheel-drive when needed. The vacuum lines for the four-wheel-drive axle disconnect system seem to always get unhooked or melted. You can easily examine the position of these lines by lifting your Jeep and tracing their position from the shift motor to the transfer case. All the plastic housing around the vacuum harness must be removed to spot these peculiar colored lines. Also, you must be careful to not break any line during the examination. 

You can easily reconnect the vacuum hoses in the right order on your own. The four nozzles on the vacuum switch must be located. These serve to control your front disconnect system for the four-wheel drive. 

You’ll need to spot the red line emerging from the transfer case and connect it to the original red hose situated behind your air cleaner. This red hose typically hooks up to a constant vacuum source of the intake manifold. 

Locate the yellow hose that directly connects to the shift motor. This line would go into a two-line plug situated vertically on the shift motor. Spot the blue hose and ignore it. This one just includes a check valve that doesn’t need any interference. 

Spot the hard black hose that serves to connect one of the yellow hoses to the shift motor. There will be a plug at the top. Then spot the soft black hose that connects into the plug at the firewall at the battery. The green hose reaches into the shift motor on the front axle and lies horizontally on the axle shift motor. 

If any part of the original line hooked to the vacuum source is missing, you’ll need to find a port on your intake manifold that is equipped with a constant vacuum. 

Your vacuum switch could be problematic

A fault in the vacuum switch on the transfer case could also cause problems in your four-wheel drive. This switch is fed by four vacuum lines and is quite easy to spot. The switch has four nipples where the vacuum hoses can be directly connected. The four vacuum hoses merge into a 1 to 11/2 diameter connector. This connector plugs into the nipples. 

You can easily solve any issue with the vacuum switch on your own. You’ll only need to retrace all the vacuum hoses from the switch and make sure that all of them are connected securely. The switch connection consists of a vacuum harness with four ports. You’ll need to unscrew this switch from the TC for proper inspection. 

Then inspect the ball-bearing plunger located at the bottom of the switch. This can easily get jammed inside the switch. A few bangs would release the ball-bearing that is jammed inside the switch. In case this proves unsuccessful, you can purchase a new vacuum switch. You can then reconnect the vacuum harness on top of the new switch.

This setup can be duly tested for adequate four-wheel drive functionality by driving on a low-traction dirt road. You can engage and disengage the four-wheel-drive during the drive to assess its functioning. 

Jeep Wrangler Four-Wheel Drive Won't Engage

A 4×4 Posi-Lock upgrade would be more dependable 

A 4×4 Posi-Lock upgrade is a permanent cable replacement for the vacuum and electric four-wheel-drive systems. This lets your drive remain inadequate control when you engage the 4WD from the dashboard. This upgrade removes the infamous vacuum hose system and replaces it with a manual cable for efficient functioning. 4WD can be disengaged from the front axle by a simple pull on the cable if you have engaged the transfer case. 

The operation of a Posi-Lock system is rather easy. There should be no acceleration on the throttle during the operation of this system.

Conclusion 

An inadequate four-wheel drive may prove to be dangerous on your Jeep in certain scenarios. It is quite important to maintain adequate control over all your wheels when the road is slippery. Assess your vehicle’s four-wheel-drive system with the help of a qualified mechanic and correct the underlying issue as soon as possible. The safety of your Wrangler should never be compromised. 

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