gm factory remotestart cell phone project

My plan is to activate the factory remote start on my 07 Chevy Avalanche via prepaid cellphone.

I refuse to pay for the overpriced Viper system, and OnStar  MyLink is only supported on select 2010 models.

The idea is simple, and if I had any of my previous aftermarket systems, it would be cake to tie into the gnd start  trigger to accomplish this.

But unless someone can shed some light or provide prints of the factory system wiriing my plan is to basically emulate what I would do by hand with the remote.

The circuit would initiate on the first + pluse of the cell's vibration motor

For the remainder of the 2 minute ringing cycle, it would have to ignore any addtitional pulses from the vibration motor.The doner remote would be hardwired, allowing the circuit to complete a 1sec lock press, followed by a 2sec Start press.I began sketching this up using several 555 timers set a one-shot's. But am asking for some help from the more experienced designers out here.  I'd like to avoid relays and stick with Resistors/Capacitors for timing.

Any help is Greatly appreciated.

For those concerned about the saftey of starting the vehicle from afar, fear not. 

Its always in an outdoor garage, the max run time is GM hardcoded to 10 minutes with a maximum of 2 cycles before requiring an actual key-start.

The cellphone will also be configured to accept calls/txts from a predetermined list of approved numbers to avoid accidential activations from wrong numbers.

Thanks again

I have done this plenty of times on aftermarket remote starts with a WHITE/ blue activation input. However, to do this with a factory remote start, you will have to open the BCM and start testing transistors for a negative signal upon pressing the remote start button on the transmitter. Much less time consuming just using an aftermarket one way system (you can find a ready remote system for under $50 on ebay)...

Digging in  the BCM could be a project for another time, but I would need prints to even get started.

Really want to avoid piggybacking another remote start (have a $20 ebay one sitting in a box)

I want to approch this as an add-on for the key fob.

Have a few family members with GM remote starts and need to make one universal "timing" circuit to hardware onto each of the remotes.