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I have a 92 base model coupe. It had an aftermarket radio when I bought it, and it came with the dreaded flashing "SYS" light for CCM (module 1) Code 72 (LCD/LED dimming circuit open or shorted to ground). I've done more research than I care to admit, and searched all the threads I could find. I have a copy of TSB 93-68-9A. I got the two 1K ohm, 1/2 watt resistors and tapped them into the grey/black and purple/white wires and connected them to an ignition switched 12V source, and it didn't stop the dang flashing "SYS" light. Any ideas where I could be going wrong? I know there have been quite a few discussions about this, but there are none that I can find that follow up with a fix that works. Thanks for your help.
This is a guess as I am a factory only type of person but I would think the resistor would need to be in line and not tapped into the wire because electricity flow to path of least resistance...it would have no reason to add the load to the wire just being tapped. I would cut the wire and put it "in line" . Also, you may want to post for help from a member in your area that may have a Bose head unit on the shelf that you can plug in just to see if you can clear the code.
Thanks for the input! And ihatebarkingdogs, thanks for the great explanation. I pulled the picture because I was confused about which gray-black wire to use (there are two gray-black wires on that same plug). I did a lot of research trying to find the correct way to fix that irritating flashing "SYS" light, but was still not 100% clear. If you are interested in what worked, read on.
The Service Bulletin that applies to this is: 93-68-9A. The bulletin says to add a 1K ohm, 1/2 watt resistor to two car harness wires and then connect those to a 12 volt ignition switched source. When you look at the diagram that comes with the bulletin, it shows that the connections are to be made to a purple-white and gray-black wire to a 12 volt switched source. The diagram also shows the wire colors changing to orange and white-red wires. Apparently, the stock Bose radio has wires and plugs coming out of it, and those wire colors change where they connect to the car harness plugs. Car harness side wires that you need are purple-white and gray-black. The radio side wires are orange and white-red, so forget those colors. Confusing if you don't know that the radio itself has wires and plugs coming from it because the car side plugs also have an orange and a red-white wire too (see picture). The car harness has two plugs that connected to the Bose radio. One has eight wires, the other has six. You need the six wire connector with an orange wire, a purple-white striped wire, two gray-black wires, a green-white wire, and a light blue wire. The wires you need to connect the resistors on are the purple-white wire and the gray-black wire right next to the purple-white wire. I originally had it hooked to the second gray-black wire from the purple-white wire, which is a no go. I connected a short wire (pigtail) to either end of the resistors and covered it with heat shrink. I got the resistors on Amazon for a few dollars. Next, I connected one end of one resistor wire to the purple-white wire tap and the other end of that resistor wire to the 12 volt switched source going to the radio. The second resistor connects to the correct gray-black wire and then to the same 12 volt switched source. Make sure you have disconnected the negative lead on the battery before starting all this, or things might get expensive. Once you've made the connections, reinstall everything, and reconnect the negative lead on the battery. Check if the module 1 code (72/74) is clear and if not, clear it and verify that the stupid thing isn't flashing any more.
Sorry for the long writeup, but out of all the posts I read (over and over), I still wasn't sure which wires to use and thought the details might answer somebody else's questions. Hopefully this helps anyone with the same problem. If I can answer any questions about this, I'd be more than happy to. That flashing SYS light was driving me crazy and now it's gone.
Thanks again for your help. I greatly appreciate it. I suspect there are more than a couple who might have this problem and hopefully this will help them get rid of that dang flashing SYS light.
When I saw this thread yesterday, my recollection was that it was a pur/yel wire. So I got out my FSM to confirm the wire colors, and yes it is pur/white (my recollection was wrong). I also saw the TWO gry/black wires, and going by the circuit descriptions I deduced that the correct gry/blk was in Cavity #3 which is right next to the pur/wht in Cavity 2. Because you didn't have Code 74 which is the pur/wht wire, I felt you had the "fix" correctly wired for the pur/wht. Looking at your pic, I saw that the correct gry/blk was wired, I didn't have any other ideas, so I let it ride. This morning I responded to Corvette 95's input, so his response wouldn't confuse you. And now you understand what the "fix" accomplishes. (Drives the circuit high, so the CCM can detect a change of state when it runs the diagnostic).
Pretty cool that you stuck with it and solved it on your own. Congrats.
Originally Posted by ihatebarkingdogs
The other end of the resistor is supplied with 12 volts when the key is on. 1000 Ohms dev by 12 v = .012 or 12 miliamps.
What the "fix" does is load the circuit to 12 Volts, or a "high" state. The Code 72 diagnostic pulls the LED circuit to low, then high, then low, then stops. If it doesn't see the state change from high to low to high, it sets the code. The 12 miliamps of 12V current can easily be sinked to ground by the CCM, pulling the circuit low.
The OP has installed and wired the fix correctly. (He took down his pictures, but he had tapped the correct wires at the radio connector). There are some other things that can be checked that may be clues as to why 72 is still setting. One thing I had never paid attention to in the 72 diagnostic is that it will only run and set when the dimmer request is not 0% or 100% dim. So try leaving the dimmer wheel at full brightness and see if the code stops setting.
But he has the resistor wired correctly. As long as it IS getting 12V with the key = On.
Glad you got it fixed, OP! Saving these posts here for future generations to benefit from.
'92 CCM Code 72 (Driving me nuts)
