4wd not engaging front wheels


Asked by markmaki Jul 27, 2007 at 02:57 PM about the 2002 Chevrolet Tracker LT 4WD

Question type: Maintenance & Repair

The front wheels will not engage and the light will not come on the dash when I shift into 4wd.  What is the usual problem?

9 Answers


Hi markmaki, If your Tracker shifts into 4wd electronically, you may have a blown fuse or bad switch. If it's shifted into 4wd by a shift lever your linkage may have come apart. Either mechanism could fail shifting into 4wd if the front differential is not working properly. You could have low lubricant levels or a stripped gear thus not allowing the differential to engage. Good luck!

7 out of 7 people think this is helpful.

Actualy this answer is all wrong, but thanks any way. I found the problem is a small air compressor mounted behind the license plate which is broken and not running right. It is called the actuator pump and it blows air into the front drive shaft to lock the wheels into the gears. It is a very small part and costs $325 from the dealer and installs in minutes.

15 out of 15 people think this is helpful.

The front diff is also a known issue. There are a series if diaphrams that hold the pressure from the air pump. This can be tested by disconnecting the pump and using a compressor in its place. If the pressure holds, the diff is ok. If it fluctuated, the diaphram is shot. Because of it being a known problem, you can get dealer rebuilds (12 months/12,000 mile warranty) for about the same price as rebuilding the existing diff. I went through all this last spring. I had to replace the pump and diff on my 99 Tracker

3 out of 3 people think this is helpful.
Paul Davis

Even though the front hub are auto-locking,,, it takes a partial to full rotation of the tires them selves to be able to enage the drive system from the transfer case/or transmission.

3 out of 3 people think this is helpful.

Its usually the actuator. I will rebuild your actuator or sell you a rebuilt one 1/4 the price of new. But first lets determine if its the problem. troyobe88@gmail.com

13 out of 13 people think this is helpful.
Dennis Perkins

I have the same issue. 4WD light flashes, front wheels engage but disengage almost immediately. HERE'S THE KICKER, 4WD works in reverse?!? but the light still flashes. WTH?

6 out of 6 people think this is helpful.

Sounds like your Actuator Pump is bad, that is generally easy to determine from the light blinking. It is likely the actuator will fix your problem. Going in reverse may take slight pressure off the slider within the differential and allow the failing pump to develop slightly more pressure to grab 4WD temporarily. Also now the rear wheels are pulling. At is core your pump can't develop enough pressure to move the diaphragm slider within the diff. Contact me directly via Troyobe88@gmail.com if you want me to test and/or rebuild it for you. Also, for ALL READERS, make sure your tires are all the same regarding wear. That can cause engage and disengage issues but not likely the issue here. .

8 out of 8 people think this is helpful.

If you need additional and extensive guidance on testing the Actuator Air Pump, Actuator, pictures, refurbished and new pumps, please visit my website ActuatorPumpRepair.Com. Also, please keep CarGurus in mind for future car questions

3 out of 3 people think this is helpful.

I want to add clarity to my earlier answers as I used the word Actuator in a place where I intended to say Actuator Pump. The ACTUATOR PUMP (outside the diff and easy to replace), also known as Actuator Air Pump, Air Pump or compressor, is a small air pump that puts 5,4 to 8.25 LBS of pressure into the Actuator. The Air Pump is a pressure pump despite it sometimes being called a vacuum pump. The ACTUATOR (within the front differential) is equivalent to a balloon. When air is pumped in it expands and engages the gear within the differential. The actuator either holds air or is doesn't just like a balloon. So engagement issues are usually the pump, disengagement issues are usually the pump, blinking light is always the pump, if a pump runs for 10 seconds and then shuts off it is the pump as it should run 3 seconds then shut off and stay off and the 4 wd light indicator should be on. A blinking light means the pump keeps coming back on and reengaging the 4wd. The actuator wasn't made to keep expanding and contracting and the differential doesn't like it either, you will develop other problems. On the website I have pumps, Differential bearing & seal Kits and other support information for testing the pump, actuator and electrical.

4 out of 4 people think this is helpful.

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