My check engine light has been on and off for some time now. I had my 99 4Runner in the shop to have it fixed and the CEL was off for a while. I had to pull a stump out of my yard and when I engaged the 4 wheel drive the CEL came on again. I drove it for a while without diagnosing the problem. I recently took a trip to see my folks. It's a 300+ mile drive. Before we made the trip back, I needed to add some components to my Alpine CD Player, so I unhooked the battery.

Got everything done and hooked the battery back up. Started the car and the CEL light was off. Drove home on I-10 over 300 miles and the CEL stayed off.

Last night, I took my wife to one of our favorite dinner spots, and stopped along the river for a quick sunset view. I had to use 4WD to get back on the road, and sure enough, when I engaged 4WD, the CEL came on again.

What could be causing this and can I fix it myself?

Many thanks in advance.

Local auto parts store. Get them to read it.
Then fix it.
:wabbit2:

yeah, really hard to proceed without knowing what the CEL code is, just gotta get it checked. for trucks our age, something to read codes is a good tool to have around.