1995 suburban 2500, battery problems, everything shuts down

antitheft system fitted use remote controll to reset antitheft system

Try turning the door key in the rear door hatch lock, lock-unlock-lock. That should shut down the factory security system.

have your battery load tested and have your alternator output tested

check for loose battery cable or loose engine ground

Start by charging your battery fully and see how it runs from there, then connect a multimeter to battery and observe voltage as it's running. Make a note of voltage before you start it and watch to see if it drops as truck is running. Try a few accessories like heater etc, to see how bad it draws voltage down. If charging circuit and alternator are good, voltage should maintain or increase. Be sure to look for obvious things first like poor/dirty connections at battery and alternator, as well as belt condition and tension before you go spending money on a new alternator.

i'm having the same issue. Dealer said the battery won't hold it's voltage; swapped in a new one. But also said that's independent of the "service security system" fault; which they say might be the ignition module. Were you able to fix your problem?

IF IT IS A I6 CHANGE THE CRANK SENSOR

If the starter is turning the engine, try re-setting the security system (leave key on till light stops blinking.) If the starter does not turn, you may have some success in re-setting system, if not you need to check battery voltage and voltages in starter system till you find the problem...can be something as simple as a bad connection at the battery. If you need help with further testing, just ask.

try this it might work, turn key to on and let set for 15 mins or so, shut key off and try to start, had this happen with passlock systems.

You need to either replace the ignition lock cylinder or bypass the security system. If you need help with either one, repost.