5.3 GMC pickup odd starting problem

[cool]

You are correct that the system does not use a resistor key. However, the passlock sensor IS looking for a specifed resistance value that your key creates within the lock cylinder. you can learn the system to the key, but if it continues to fault after you do so, you need to replace the passlock sensor.

[summy670x]

You are correct that the system does not use a resistor key. However, the passlock sensor IS looking for a specifed resistance value that your key creates within the lock cylinder. you can learn the system to the key, but if it continues to fault after you do so, you need to replace the passlock sensor.

Yeah, based on the fact he's used multiple keys, i'd put bets on the sensor as well.

[texfc]

You are correct that the system does not use a resistor key. However, the passlock sensor IS looking for a specifed resistance value that your key creates within the lock cylinder. you can learn the system to the key, but if it continues to fault after you do so, you need to replace the passlock sensor.

Thanks for the help.  Now I think I understand!  The pass code reader looks at the cuts in the key and sends a code to the BCM / PCM based on that key.  If it is different  than the key in the memory, the PCM won’t let the engine start.  Even if mechanically the ignition will turn, the key must still match the one in the memory.

[texfc]

Replaced the ignition lock cylinder, did the 30 minute relearn again, and it has started 6 times so far.  Giving it back to my stepson and keeping my fingers crossed.  The ignition key and the door keys will be different now, but no big deal, older Fords were always like that. 

[gc3]

not sure if its true, but i heard once that if you unplug the bcm while the truck is running, it will automatically assume a bcm fault and bypass vats for you in the future

[lsxtacy]

ok im definitely going to diagnose it as the ignition key lock cylinder, my friends malibu acts the same way.....try this turn the key back to the off position after it has sat a period of time "quickly" rotate it all the way to the ignition position without lagging in the on position at all........see if it will stay running after it re-engages into the on position

[texfc]

I replaced the ignition key lock cylinder Sunday night and haven't received a "help, I'm stranded" call yet, so I think that was it. 

[lsxtacy]

good deal man glad to have been able to be of at least some assistance lol