TECH II Help Security light flashing

[la1]

I have a base model 2003 Impala 3.4L The security light keeps flashing the car will not start . I tried letting it flash for 30 minutes hoping it would relearn. I think it is the tumbler / key switch. Want to make sure it is not wiring or the BCM. I have access to a TECH II and a while ago I read where with the tech II you can see the voltages for the passlock when the key is turned, there were several more voltage readings , so where in the TECH II are the parameters to read and what are they and what should they read or what voltage levels.

UPDATE I found where it is its in security data. BTW when I got home from work my car started right up

[Colt Hero]

I agree the problem is most likely in the ignition switch/cylinder/Passlock Sensor assembly, but this has never been definitively proven. The best theory going, I believe is the one about the contacts needing to be cleaned (or even soldered permanently).

What I'd like to know is, assuming it's the contacts (oxidizing), if the r-code value back to the BCM is actually changing, and by how much. And whether or not the BCM is "re-learning" this modified value. OR, is it just a case where the r-code is simply 'dropping out' for too long a time (maybe just a second or less), and the BCM is declaring a malfunction, posting the SECURITY message, starting the 10-minute wait timer, and "re-learning" the same old value.

If you have access to a TECH II, it'd be nice to know if the BCM is looking for a PARTICULAR value for *your car*, or if it's just a table of values where the r-code can be ANY of the values in the table, or even within a range of each of the values. And, as I already mentioned, it would be nice to know if the r-code is changing with oxidized contacts.

[Tech II]

Since you have access to a Tech II, were there any "P" or "B" codes set?

I assume we are talking PassLock? If yes, then a B2958 or B2960 should be in history if not cleared....

Naturally, there is potentially a problem with the PassLock sensor itself, but also there have been connection problems between the sensor and the BCM, at the BCM connector(harness)....

[la1]

Well it was after a really big snow, I ended up walking to work and back home. When I got home my Impala started right up. I don't know if this makes sense or not. The night before I drove through some high snow right before I parked the Impala, maybe snow got in the starter and melted then froze. When I arrived back home that night it was above freezing