5.3 GMC pickup odd starting problem

[texfc]

My stepson has a ’99 GMC half-ton pickup with the 5.3.  The engine starts immediately, but then dies as soon as you release the key.  Not a sputter and die, but just like you turned it off.  If you leave it for a day with the battery disconnected, it will start and run just fine after you reconnect the battery.  It will start ok for the next week or so, then the problem comes back.  Any ideas?

[gc3]

sounds like vats.
try a different key?

[texfc]

Yes, I tried both keys. The truck does not use a transponder key, but it does act exactly like when you try to start a transponder key car with a non-transponder key. 

[lsxtacy]

does it run for a moment and then die or as soon as you release the key back to the run position? sounds like someoby isnt getting 12v somewhere.....bad ignition lock cylinder?

[texfc]

It dies as soon as you return the key to the "on" position.  From what I've read on line about it, it's the GM security system turning it off, but I haven't found a definate answer on how to correct it.

[lsxtacy]

hmmmmm well having workin the automotive custom audio/security industry for a few years i can tell you ive never seen that lol but is entirely possible those things can be finicky. id trailer it to a local dealer and have them reflash it to remove the security issue, as long as you have proof of ownership  they should be able to assist you with that, if not the only other solution would be to take it to someone with hptuners or efilive and have them delete the vats from the ecu lol

[odat]

I had a pontiac in my small shop here and it was acting pretty much in the same manner. The tumblers in the switch were bad, I couldn't 100% trouble shoot it so he took it to the dealer and they found it. I think they allowed with the tumblers bad it would not engauge the slider switch all the time. luck to ya.....

[yamaha]

As dumb as this sounds. Put he Krystal in the ignition to on for ten to fifteen minutes. After that, turn it to off and to start it again. This happened to my wife's sister Malibu. The passive lock made the same exact symptoms. Hope his helps.

[texfc]

Tried it, no luck.

[cool]

Does the security light flash, go out, or stay on solid after it dies?

[texfc]

After it dies, the battery symbol shows first, then the security light flashes 5 times then it shows change engine oil.  Fuel rail is at 52 psi when it dies.

[texfc]

Got a guy to read it with a much better scanner than mine.  1631 - wrong or missing pass code from the body control module.  Did the 30 minute relearn procedure, and it starts now.  Why does it keep loosing the pass code and is worth trying to troubleshoot, or should I just find someone who can re-flash the PCM to ignore the VATS?

[summy670x]

Got a guy to read it with a much better scanner than mine.  1631 - wrong or missing pass code from the body control module.  Did the 30 minute relearn procedure, and it starts now.  Why does it keep loosing the pass code and is worth trying to troubleshoot, or should I just find someone who can re-flash the PCM to ignore the VATS?

From what I remember, the VATS system used a very limited amount of resistance values to determine the correct key.  It's very possible that the key is worn, I just don't know 100% which system is on your car without seeing the key (all google results point to passlock II though). 

http://www.directedstore.com/manuals/20402.pdf

That link has some directions on how to determine the resistance value of your key.  Once you determine the value, you can wire in some resistors and have the passlock II always bypassed.  Just don't ask me how I know

[texfc]

Unfortunately, it does not use a resistor key.  The PCM looks for a code from the BCM, don’t ask me why, but somehow it’s related to anti-theft.

[texfc]

Lasted for 3 starts, then lost the code again.