2003 GMC Sierra 2500 HD Q&A
2003 GMC Sierra 2500 HD Question: Thief Lock shuts off fuel or spark?
It sounds like you may be having problems with your passkey system. Did you replace the ignition switch? The easy start would be to put the key in the ignition and turn it to run for about 3 seconds. Now release the key from the start position and let the vehicle sit with the key on engine off for 10 minutes no less. this will relearn your passkey. After 10 minutes turn the key to the off position then try and start the truck again. Be sure your battery is fully charged before starting. I know you said there are no codes but did you check the theft deterrent module for codes or just the powertrain control module? - gmc4me