Join Date: Jun 2006
Location: Eastern ON Canada
Car: 07 OBW 2.5i D-4AT
Feedback Score: 6 reviews
Yes, the "door open" warning lights in the instrument panel can be a great help in diagnosing this.
The body integrated unit, which is the module that slowly turns the light off, is not prone to failure (although I guess it can happen).
The switch has three positions, ON, OFF, and door. "Door" is the middle position (at least, on my 07), but have you checked the other two to see if the light responds to the opening and closing of the doors? If this is a problem that was there when you bought the car, I wouldn't discount the possibility that the previous owner(s) did some wiring modifications that is causing the light to stay on, or there's a short to ground in the wire between the dome light switch and the control module.
When the driver's door is opened, in addition to the dome light, the ignition switch area on the steering column should be lit by a red ring. When the door is closed (before the key is inserted) the dome light will (normally) dim to about 50% and then, about 10-15 seconds later, fade out. The red ring around the ignition switch should go out at the same time (after 10-15 seconds). If the red ring light does eventually go out, but not the dome light, it could suggest that the BIU light control is working. In which case, I'd look for a problem elsewhere before targeting the BIU.
Last edited by plain OM; 09-21-2011 at 08:53 AM.
Reason: add tests