02 Blazer wont Start, Passlock?

This is a Passlock system. See this post on how it works, what goes wrong and how to do a reset

http://ricksfreeautorepairadvice.com/passlock-fixes/

You MAY have a couple of problems here and I've experienced them all on my 2000, but first things first. Check your brake switch wiring harness next to the fender under the dash (where the wire is too short and may shortout). Make sure it's not burnt, or you'll be chasing this forever like I did. If it is, replace the pigtail up there. If that is ok, jiggle your hazzard light switch and see if they start working again. If they start working, replace your hazzard light switch. If it's not that, it's your multifunction switch. Your lower brake lights run through the multifunction switch.

This same problem has affected many people, you're not alone.

Check the GM recall list on this vehicle. There are problems with the multifunction switch, and the hazard light switch. The recall actually shows you what to do to narrow down the problem. Brake lights run through both of these switches. I just went through all of this, ended up being a burnt female connector that goes into the brake light switch. Up on the brake pedal.

Check for 12 volts coming into the brake light switch. If you have that you should have 12 volts exiting the switch when the brake pedal is depressed. If you have that and the center brake light works you have a problem with the turn signal. If the center light doesn't work you probably have an open in the brake light circuit between the turn signal switch and light bulbs. If there is no voltage at the brakelight switch you have an open circuit before the switch. I'm assuming the fuse is good.

is very well could be, if i were you i would check the relay, and fuse for the throttle body injector, if thats good, i would change the fuel filter, if no luck there, i would say you are needing a new throttle body injector. See if you can get somebody to turn it over, and see if the injector is shooting fluid down the throttle body, if not you know its fuel related....This week I had a family member that parked his vehicle, went out the next morning to get in it, wouldnt start, 3 days he went without a vehicle, so i went down and looked at it, he was trying to start it with a key he had made.. i noticed the theft light flashing, i had him get his original key given to him by the manufacturer, put it in the switch, and it started right up.. dont know if that is the case with yours, but hey its a thought.
hope this helps

Does the third brake light still work? A common problem that can cause this is a multifunction/turn signal switch. GM has a recall on this but you would need to contact your local GM dealer and have them run your vin number too see if it qualifies for that campaign. The recall was issued in 2002 but to my knowledge is still an open campaign.

bad earth/ground in the light clusters causing power to use other bulbs as earth / ground

same just happend 2 me,was told it was the neutral safety switch -but didnt start in neutral-took 2 shop 400 later it was the ignition switch runs great again hope i helped

When my blazer did this they had to replace part of the wiring harness in the steering wheel. It took forever for them to get the parts because we live in nowhereville, but once it was in it works again and no problems. I had to take it to the actual chevy dealer because none of the other places had a clue. good luck.

First of all make sure all your battery connections are Clean and Tight. If they are and all your dash lights come on and its not starting But its cranking over Your anti theft alarm may have gotten activated. You may have to leave your Key in the On position for 20 minutes to reset the alarm. Not cranking just in the on position, Now if its not Cranking and your hearing a clicking sound it may be your starter. I have sometimes tapped on the stater with a deadblow hammer and had someone crank it over Making sure your in park foot on brake and being EXTREMLY Carefull that you are not going to run someone over. If that don't get you going Get back to me we can do some more trouble shooting. Get that thing going for you. Thanks, Bear001