<hr style="color:#000000; background-color:#000000" size="1">Tried starting 98 C5 yesterday, battery was completely dead. Charged overnight and had 12.84 measured at battery terminals. Reset key fobs and they locked, unlocked and opened the trunk. Lights, horn, radio and heater blower motor all work. The key = is NOT vertical when ignition is off and key is out of ignition but is almost on the dot on the plastic to the ACC position. Tried starting car. All gauges go to zero and accessories turn off but starter will not engage.
Turning key to the off position still leaves radio on with driver door open. I suspect this is what caused the batteryvto drain, when it should be off it still supplies power to accessories.
Used a different ignition key to make sure that it simply did not read the resistor pellet wrong.
After removing key found that you can turn the ignition switch lock cylinder into all positions WITH NO KEY. Used the tip of the key and was able to turn the metal part of the switch where the key is inserted simply by twisting the metal lock cylinder clockwise.
Pulled codes and got the following codes:
BCM B2721 H, B2722 H, B2723 H C VATS codes
LDCM U1096 H
RDCM U1096 H
RFA U1255 H
Suspect ignition switch lock cylinder and/or the actual electrical portion behind the cylinder. Can the interlock cable to the shifter be causing the reason why the switch will not return completely to the OFF vertical key position?
Should I try the VATs relearn procedure (3 times ignition on then off then on (10 minutes at a time) as the battery was dead for some time or will this screw up things worse than they are now?
Can anyone shed light on the cause and fix for this problem?

 

How old is the battery? What does the battery read now?
How long was it connected before it died?

I disconnect my battery on my 94 f-body for months/years without vats issues.

Haven't had any issues with key cylinder turning without key.

 

I have a 2002 trailblazer and for some reason the ignition won't go into the off position. I went shopping and when I came out the The battery was dead. It took about 10 minutes to jump it. When I got out the radio and lights went off like normal so I didn't suspect anything. After the jump it'll switch into the off position. I can also start the truck and take the key right out.... Is that the issue?