I have a C5, 2003 50th Anniversary Edition convertible. The car is in good shape and everything works great - until it rains or I wash it. Recently, within the past month or so, whenever it encounters rain or washing, strange electrical errors occur. First, the windows and door locks wouldn't work on both sides. Next time, just the right hand door windows and locks. The next time, several issues occurred, traction control, reduced power, active handling, the radio went off for about a minute, then came back on. Both windows, locks, mirrors, settings memory, etc. This last time, nothing on the lh door functions at all (seems to have no power) and when I checked the codes, the code for the LDCM reports "no comm." Most of the time, after a period of time (couple of hours to a full day) everything works properly again. Evidently it "dries out".
Remedies: I checked the three drain udders for the cowl (2 on drivers side & one big one on passenger side) - clean. I checked under the rh floor board for moisture or corrosion issues - clean and dry. I checked the TAC unit and PCM behind the rh front wheel. The units were dry. I disconnected al connectors and the connections were clean and dry. I checked the condensate drain for the a/c evaporator - clean and open. I cleaned the multipoint ground in the engine compartment near the lh front wheel - it was not corroded and dry. I checked battery voltage - 12.8v. I have checked everything I am aware at this point. Any suggestions?? This occurs immediately after getting wet. Usually the car is off and sitting on level ground. I need HELP!! LOL! Anybody know of any ideas? Thanks in advance!

 

Sounds like you are having a serial data buss issue. To the left of the BCM are two thin connectors. Find the one with four wires and pop the top off that connector and see if the symptoms go away.

Is the carpet under the drivers seat dry also??

Bill

 

I located the serial bus connector in the rh floor, somewhat under the BCM. It was clipped to a plastic component that provides the support/mount for the BCM. I located the connector with the four wires and removed the top to that connector. I tried it with the top off, then replaced it and tried it with the cap replaced. Neither action had any effect on the left hand door controls. Also, since it is now after dark, I also noticed that none of the button illumination on the left hand door is lighted. The carpet on the drivers side, as well as the passenger's side, it bone dry. Neither side has any evidence of any moisture.