I know much has been written and commented on regarding this topic, but I wanted to add my 2 cents. My 2003 Z06 recently developed an intermittent issue (mostly never worked) with the drivers door lock not working and drivers door window not rolling up or down. Background: intermittently, drivers door lock did not lock or unlock from either door switch or remote, although the passenger door lock worked from either side or remote, AND drivers window would not roll up or down from drivers door switch (passenger window stills worked fine from either door switch). These two problems existed simultaneously and intermittently, in other words, when the doors locks were not working, the window was not working. When it was working, it was all working perfectly, so this told me I did not have the common relay problem these DCMs have. In troubleshooting this particular problem, there are several posts regarding the connector in the A-pillar that commonly gets either corroded or loose. In my case, jarring this wiring harness/connectors did not make the DL/Windows work again, so if you have a similar problem as I had, don't just wiggle the wire and move on if you don't get a positive result. I examined my connector and it did not initially appear to be a victim of corrosion, but when I persisted to examine it, I determined that not only did it have corrosion deep in the connector, but it also had fatigued and was no longer making an excellent connection like it should.

So: If DL and Windows go out intermittently at the same time, in the drivers door, it HAS to be something common to each system. Focusing on only what was common as far as wiring goes (refer to wiring diagram for your vehicle), there appears to be only one ground on a 2003 C5 to the DCM for every thing it does, and there are 2 power supplies from 2 separate fuses. Using a digital voltmeter, I determined full battery voltage was getting to the DCM on both required circuits (drivers door lock and window fused circuits), but the ground at the DCM had 19 ohms of resistance when measured back to a known good ground, so I had my culprit, the DCM had a poor ground through the A-pillar connector. Short of replacing the A-pillar connector with a better unit, (which may be in my future), I disassembled the connector one wire at a time so I wouldn't get anything out of order, cleaned each terminal with a (very) small file, carefully crimped the female terminals a little smaller to grip the male terminals more effectively, then cleaned the entire assembly with electrical contact cleaner. Be very careful crimping these terminals smaller so you don't suddenly crush the terminal and probably ruin it, and don't get it too small or you may have problems reinserting the male connector. It takes very little effort and an exact crimp location on the terminal to get the job done. I also carefully bent the curved part of the terminal out so it would make more positive contact. Think surgical precision, not brute force. There is a small lock tab on each terminal that will likely get bent inward when you remove the terminal from the connector, even if you use the appropriate removal tool, so you will likely need to bend it slightly out before you reinsert the terminal, so the terminal will lock in place securely. (Sorry, I do not have a picture of this small tab). Once this was all done and reassembled, my door locks and drivers window work perfectly.

In researching this problem before, I did run across some posts in other places on the Internet that said you could troubleshoot the DCM by "swapping one side DCM to the other and see if the problem follows." I highly recommend you do NOT do this, as these units are different, and although I have not examined the wiring diagrams from side to side, I would suspect the wiring is not perfectly compatible. However, do your own research if you need to go this route, just be careful what you read on the Internet. There are safer ways to troubleshoot that don't risk an expensive DCM.