p light not on when shift to P cause car won't start

[pigvet]

Hi all, recently I noticed that sometimes the P light won't light on when shifting the gear to P. Today the car didn't start. After a close check, I notice the P light is not on either. So I shift the gear to neutrol and the car started. Can anyone please tell me what the problem is? I still can shift the gear to P and the light will be on. But not always. Thanks.