A few things come to mind, since I had to trace the same problem in mine over a year ago:
If any bulbs have been recently replaced, especially in the taillights, make sure you use the correct wattage. On the inside of the taillight bulb housing, the wattage for each is embossed on the plastic near each bulb socket.
Use the european spec bulbs with the nickel receptacles (like Phillips) and not the gold anodized domestic bulbs you commonly find at Walmart. The dash indicator works primarily by a set resistance, and the metal conductivity of the bulbs can affect the total resistance.
Finally, the metal terminal strips that hold the bulbs in place can dislodge and lose contact with ground, causing the condition. You can press along each strip with your thumb and see if the light on the dash goes out at any time. I ended up bending one of the strips just enough to cause the light to go out, but a month later cracked a lens when I backed into a truck, so I replaced the whole taillight assembly anyway.
Good luck!
