I changed my battery in my 2002 chevy silverado 2500hd now when i try to start my truck ill put the key in and the security light flashes like normal but when u turn the key the alarm starts going crazy and my truck wont even turn over but u can here the fuel pump kick on but nothing will happen what do i do?!?

Is the security light flashing? If it is, put the key in and turn all the way but don't start. Leave on for 10 min. Or until the security light stops flashing. Turn off and then try to start.

If you have an owners manual it explains it in there.. I have a 2002 Chevy express van and you have to turn the key to the on position ( do not start). fully depress the accelerater twice then start the engine. this turns the oil light off in my van. ( this was in my owners manual)

may be you should make a diagnostic and you can do it in a garage or you can do it by yourself if you want to do it by yourself you need some tools and you can find some good ones here: spobd2.com

try this before replacing parts. put your key in the driver door and lock then unlock with the key, if this doesnt work you can also put your key in the ignition and turn it to the run position and leve it for 15 mins or so. then try to start.

If the owners manual doesn't tell you the procedures to deactivate the anti-theft module, you might have to call the GM dealership and ask the service department how to deactivate the anti-theft module. I think it's key "ON" key "OFF" key "ON" key "OFF" key "ON" and then wait for 20 minutes then try to start the engine. Good luck, Gary

COULD BE SECURITY THEFT SYSTEM HAS A FAULT.OR THE STARTER SOLENOID OR STARTER BAD.BUT MAKE SURE BATTERY 12.5 VOLTS.BECAUSE BATTERY STILL CAN BE WEAK AND ALL THE LIGHTS WILL COME ON.

2001 chevy silverado 2500hd battery light flashes intermittently. no problem with battery or alterntor. both tested ok. no problems with starting or running. voltage gauge reads just above 14. no problems with anything except battery light flashes. what could be the problem?

You may need to re-set the light by turning the key like you are about to start it then taking off your battery terminal, turning the key to the off position then trying it again

you messed up the vat system . the is a sensor the sensis the key some how you pulled it lose or some thing. the wires tend to break on the gm trucks and cars

that has something to do with the reprograming of your ingition key if you are having not starting problems i will recomend you to leave it alon but if you wnat to be in the safe side then call one of the mobile locksmiths guy or take it to them to see if the key has to be reprogamed, and try using only one single key for the ignition,
some time systems take a little be to reconigse a copi made key