Okay, so this morning im driving on the highway, and all of a sudden my check engine light comes on and my speedometer drops down to zero. Truck does not stall or anything, but I pull over. First thing I check is the oil, and it is pretty low. I add a quart and the level seems fine. I continue on the rest of my journey, truck seems to run fine, but the check engine light is still on. Also, the speedometer still stays at zero and the odometer has stopped ticking. What is the problem. I am going to take it by AUTOZONE and have them run the diagnostic test. ANYONE have an idea. Its a 1994 Nissan XE pickup.