Jeep Cherokee Forum

Jeep Cherokee 1984-2001: Why Won't 4WD Engage?

If your Jeep Cherokee's 4WD won't engage, keep reading to find the source of the problem and get you off-roading once again.

By Brett Foote - September 2, 2015

This article applies to the Jeep Cherokee XJ (1984-2001).

While complete failure of a 4WD system isn't common, Jeep Cherokees are known to eventually suffer from a busted vacuum line or a bad indicator switch. Modern systems rely on vacuum pressure and electronics to shift between 2WD and 4WD, which is a big improvement over the old days when you had to get out of your truck and manually lock the front wheel hubs. If your truck has decided that it no longer wants to drive the front wheels, we've got some tips to help you figure out why.

Materials Needed

  • 1 1/8" wrench
  • Voltmeter
  • Vacuum gauge
  • Vacuum pump
  • Floor jack and jack stands

Step 1 – Check 4WD indicator switch and plunger spring

The first thing to consider is whether your 4WD light is coming on or not. If the light doesn't illuminate and your front axle doesn't engage, you might have a total loss of vacuum. If the light is not illuminating when you shift into 4WD but the front axle is engaging, you probably have a bad plunger spring inside the switch. The switch is located on top of the transfer case. It provides a ground for the dash light, so you can remove the switch (1 1/8" wrench) to see if the plunger operates properly and use a voltmeter to check if the switch is working properly. Either part is available for around $10.

Figure 1. New plunger spring (bottom) vs bad plunger spring (top).

Step 2 – Check your vacuum lines

Loss of vacuum pressure from a disconnected or damaged hose is the most common cause of 4WD system failure. First, check to see if any hoses have come loose or even completely disconnected, and check to see if any are rotted, split, or damaged. Once you have verified that the lines are in good condition and connected, check your vacuum pressure and compare it to manufacturer's specs. If everything looks good but you still get no vacuum pressure, it's likely that your vacuum shift motor is bad (Step 3).

Figure 2. Vacuum line diagram for 1987 to 1990 Jeeps.

Step 3 – Test vacuum shift motor

Disconnect the vacuum harness from the axle shift motor and connect a vacuum pump to determine if there is vacuum present at the port where the indicator light is connected. If there is vacuum present, the shift motor is functioning properly. If there is not, the motor is bad and must be replaced.

Figure 3. Troubleshooting the vacuum system will help you track down any leaks or faulty parts.

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