Stryker7

Bought this beautiful 93 40th Ruby with 40,000mi and the first mod I couldn't wait to do was remove the sick sounding buzzer that would come on when I would open the door. When I would close the door, it wouldn't go off for several seconds. The only exception was if I opened the hatch, closed the door then closed the hatch...then it would go off. So a few months go by and I started driving the car more at night and noticed that my courtesy lights don't come on when I open either door. But they function correctly with the hatch. I have no idea whether these issues are linked but I started getting a SYS flashing on my CCM so I drilled in and found it was a code 25 in both C(current) and H(History). Pulled the negative on the battery terminal and SYS came back immediately. Am I dealing with multiple gremlins or is this all tied to the buzzer? I did find a blown 5A LH Courtesy fuse but I replaced it with no improvement to the courtesy light issue. BTW, the interior lights all function correctly using the headlight / dimmer switch....any suggestions?

rodj

Code 25 shows the CCM is seeing a open circuit somewhere on the courtesy light circuit.
Really need a FSM with the circuit wiring to track through to find fault

Sandpiper59

I just went through all this with my 87. When the PO installed the 90 dash they took a lot of short cuts including the wiring to the CCM for the lights. You cause won't be the same as mine but that is the code I had to deal with.

The CCM can be tested much deeper, you can take it to a section where it will tell you if it sees the doors open or not and if it can turn on lights on its own etc. The CCM watches the door switches for a ground, a ground on the door wire means you opened the door, when it sees this ground, it sends a ground to the light relay (which always has 12v on one side) causing the relay to close. Code 25 from memory means it isn't seeing the 12v on the relay prior to grounding the coil feed.

I have the pin out for the CCM somewhere but it is so ignorant to get to, behind a steel plate which is behind the radio. The relays are behind the carpeted cover above the passengers feet, they are not labled so you have to sort out which one it is.

vetteoz

Stryker7

Excellent layout Vetteoz! So my troubleshooting included (1) re-inserting what I thought was the sick door buzzer which, according to the diagram above, was actually the Courtesy Light Relay. I dont know why the buzzer would have gone off when I pulled the relay or why my courtesy lights worked with the hatch with the relay pulled. (2) I then took the negative terminal off the battery to reset the SYS codes, fired it up and vwalla... I have interior courtesy lights, no codes or blown fuses and ironically no more buzzer. I did shoot some WD40 in the door switches the night before to clean out the contacts (just in case) but now everything seems to be in order. I didnt make the connection between the relay that I had removed (thinking it was a buzzer) and the courtesy light problem until I looked at the diagram above. It appears to be a combination of things and I am glad it was not more serious.

My humble analysis: the SYS code was being thrown because I removed a relay that opened the circuit which is why the CCM was throwing the Code 25. The blown LH Courtesy Fuse could have been part of that 'open circuit' issue as well but I have no idea. Why the buzzer went away when I removed the Courtesy Light relay is still a mystery. Thanks for everyones input, analysis, diagrams and help. Hope this helps someone else down the road.

A full comprehensive list of CCM (not ECM) codes would be great to post here so when SYS is presented for other reasons, everyone has one place to go. I did searches on CCM codes for days and couldn't find anything. Can you assist Vetteoz? We can just put those adjacent to the diagrams.

Here is the website I used in concert with personal help from UPSETVETTE to access the CCM codes from my 93. This site addresses how to access ECM and CCM codes. Once you jumper the port, you can use the fuel and trip buttons (used to normally access fuel economy, Trip ODO, etc) to navigate through the various prime and sub-menu's.

http://www.corvettephotographs.com/c4vettes/codes.htm