Ok, it appears now that there's a whole new wave of column lock issues again most likely because C5 owners are selling their cars and we have a new generation of first-time owners of used C5 corvettes.

What makes things worse this time around is that new owners don't know what mods have been done by the previous owner(s) and in some cases by GM. And now GM no longer supports these owners. So this will be my attempt to help you new owners diagnose what exactly you have just purchased with regard to the column lock situation.

Normally I would say to first check with the dealer to discover what GM recall mods were performed by the dealer, but it seems moot now because many previous owners have made their own mods post GM recall mods, so the dealer information cannot be strictly relied upon by a new C5 owner. So let's begin with some FAQs that I seem to get on a daily basis...

When I insert my key, I still hear the column-lock motor make a noise. Does that mean I don't have the K Harness?
No. It means you either have a stock configuration without the GM K Harness mod, or you have a K Harness. It also means you do not have a CLB installed.
When I drive my car, I hear a strange clicking noise when I turn my steering wheel. What does that mean?
This is likely a situation where the column lock motor lock pin is partially extended and rubbing on your lock plate. Since we don't know if the lock plate has been removed, you should check this out BEFORE driving your car again. This could be a life threatening condition should the lock pin engage the lock plate while you're driving!
I get the Column Lock Error and can't drive my car above 2 mph
This is the most common complaint and usually happens right after your battery has discharged or failed. What can we say about this condition? Well, we know the PCM has been reprogrammed to shut off your fuel when you get a Service Column Lock error. Can you turn your steering wheel? If not, we know your lock plate has NOT been removed, we also know your column lock motor is wired into the system, so you DO NOT have a CLB installed. So either you have a stock configuration or you have the K Harness installed. If you CAN turn your steering wheel, it means 1) your column lock motor has failed with the pin retracted, 2) your lock plate has been removed 3) your column lock motor harness has been disconnected. What should I do? Install a CLB.
How can I tell whether I have a K Harness installed or a CLB?
Can you hear the column-lock motor activate when you insert your key? If yes, then you DO NOT have a CLB. If you cannot hear the column-lock motor activate, there’s no conclusive proof because the column lock motor could be in a failed condition, disconnected or a CLB installed. The only sure way to know is to remove the knee bolster and inspect your wiring harness. Locate the connector to your steering column and follow it to the source. The K Harness will have a "Y" wiring configuration with 4 wires going to a GM relay tie wrapped to the left of the steering column and 2 wires going up to the steering column lock motor. A CLB will NOT have any fork in the wiring and the steering column lock motor harness will be disconnected completely.
I installed a CLB and I still get the Service Column Lock error. Why didn’t this fix the problem?
There are several possibilities. Usually the CLB fixes the problem, but not always. Here are a few things to look for:

1. Is your battery fully charged?
2. Did you install your CLB correctly? Some folks not realizing they already have a K Harness installed, locate the wiring harness going up into to the steering column and plug their CLB into this connector which does nothing but disconnect the column lock motor leaving the K Harness still in the circuit. Locate the K Harness and completely remove it. Then connect your CLB per instructions.
3. Sometimes while troubleshooting and working under the dash, you accidentally short out something and pop a fuse. Ensure fuse 23 in the passenger footwell is good. This fuse powers the BCM column-lock motor circuits.
4. If you installed your CLB correctly and fuses are all good, but still get the Service Column Lock error the next step is to determine if you have a secondary GM relay mod (Procedure 1B of the GM recall bulletin). There are two ways to tell: 1) the 4-pin connector where your CLB plugs into will have white, purple, green, black wires or 2) there will be two relays located just above your BCM. The one on the upper rightmost side will be the one to look at. You'll see purple, white, orange, orange, dark green wires coming from it. NO purple wire? Then you don't have the this mod implemented. If you do have this relay mod, the relay could have failed completely or may be causing switching spikes on the 12V line that triggers your CLB to change states immediately after it switched to the correct state thus defeating the CLB operation. The procedure here is a little complicated for those non-electrical types, but the goal is to remove and discard this relay and then jumper between the orange wire (pin 87) and the white wire (pin 30). Note there are two orange wires, so get the correct one! This operation often ends up with a blown fuse 23, so check it before you finish. Email me for photos and instructions if you need them.
5. So none of the above steps have fixed the problem, what now? This is a difficult spot to be in because it only leaves physical wiring faults and the BCM itself. On a few C5s we've found that water got into the passenger footwell and corroded contacts and connector pins. If this happened to you, it's a whole different ballgame to troubleshoot. Personally I’ve never seen a BCM fail in all the years I’ve been helping forum members, so my first suspicion is always fuses, wiring, connector issues or miswire in step #4.

A great article on installing the CBL is available at LS1Howto.com http://www.ls1howto.com/index.php?article=24