IT IS A WARNING LIGHT TO TELL YOU THAT A DOOR IS NOT SHUT PROPERLY
If the door is ajar and light stays on, spray some WD40 into the latch. The door switch is probably stuck. Spray all doors then open and close a few times.
I had the same problem with my car and was told it was something to do with 1 of the sensor wires. It may need replaced or may have just moved from where it is meant to be. Hope this helps.
If a door warning light stops working on a Honda then the unit can be replaced. Locate and light and purchased a new unit. Replace the unit and it will work again.
On my 2002 sportage 2-door, the door ajar light stays on when the tailgate is not locked. with the key.
broken or stuck sensor... bad thing... easiest is to replace whole lock...
Try spraying WD-40 on the door latch, the part that is on the door itself. The door ajar switch is located in with the latch. Had the same problem, door ajar light on, interior light stays on, and horns toots twice when you lock with remote, to signal door is not closed. Door was shut but truck didn't know it, WD40 fixed it.
check the sensor on the door, its probably bad
I just sprayed all my 1999 taurus door latches with silicon and it fixed it.
The issue with your Vectra 2002 2.2 DTI, where the warning indicator stays on despite the door being shut, is likely due to a faulty door switch or a wiring problem. The door switch may be stuck or malfunctioning, preventing it from recognizing that the door is closed. Inspect the door latch and switch for any debris or damage, and consider testing the switch with a multimeter. If necessary, replacing the door switch should resolve the warning light issue and allow you to lock the doors.
Check the pressure in all of the tires and inflate them to the pressure indicated on the door jam. The light should go off within a few minutes. If it stays on then you have a bad sensor in the tire or on the car.
Because one of your door sensors are broken.