hey guys. im reaching out because i have a '03 G35 for a few years now but im now starting to have a problem with my car alarm. it tends to go off when i unlock my car and open the door. i can turn the car on no problem but the alarm will continue to go off until i press the lock switches on the door enough for it to finally go silent or until it decided to shut itself off / i pull the battery. when i got this car it came with no key fob all i have is the one factory key. and as far as i know the alarm system should also be factory. has anyone else come across a problem like this? could it be the key could be bad?, or maybe i need a key fob? ive been stumped and have been having troubles trying to find an answer.

 

You should probably take it to an third party audio and/or alarm installer in your area. There may be a bad sensor that is not registering the keyfob signal to disable the alarm but it opens the mechanical door locks. I would suggest an aftermarket alarm since older alarm systems tend to have communication problems as they reach the 15 year mark, and you will have another extra key fob too. Also the viper system will have a nice blue light that can be placed on the windshield to see that it is active. I got an old alarm redone on a 15 year Honda Accord and it cost $500 in labor and another $1000 for the alarm kit. So be ready to shell out that much if you really want to fix it right and upgrade it.

 

I'm thinking this is more of a BCM issue. The BCM received the signal from the fob to unlock the door, the BCM sends signal to the door lock actuators to unlock the door, however it isn't canceling the NATS IMMU chain programming in the BCM so it still thinks the security system is engaged.

Stand right outside your door and look at the NATS indicator LED light on the left side of the dash when you use the fob to lock/unlock the door. Does it flash each time you lock/unlock? When you lock it should start pulsing a flash every few seconds to let you know the system is still armed, when you unlock that flashing pulse should stop.

What exactly is that light doing?

It's also possible that some previous owner added an aftermarket alarm system to it that is causing the problems. Take a peek under the dash and see if there's any aftermarket electronics hanging out.

 

If I'm reading the original post correctly, they don't have a key fob at all. OP, if that's true then you should get one and have it paired to your BCM.

(also the NATS light is about center dash for '03-'04)

Edit: I'm confused as to why they've had the car "for a few years" and only now have an issue with it.