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The IPC in 98 coupe was determined to be un-repairable. I swapped out the 98 IPC and replaced it with a good panel from a 99. All functions work great except for the fact that the air bag warning light is on 100% of the time and there is a SDM-NO COMM message on the DTC. I was told by a GM tech that the 98 panel is different than the 99 and the light will not be able to be turned off since communication links and wiring is somewhat different. Anyone have any experience with this problem?
IPCs can all swap. I can't recall for sure if it is the airbag light, but I know for sure there is one warning light that you have to move to a different location in the panel when switching between certain years.
Some you also had to solder in the connector for the HUD, but you don't seem to have that problem.
Last edited by lionelhutz; Apr 28, 2020 at 09:21 PM.
IPCs can all swap. I can't recall for sure if it is the airbag light, but I know for sure there is one warning light that you have to move to a different location in the panel when switching between certain years.
Some you also had to solder in the connector for the HUD, but you don't seem to have that problem.
+1
I remember seeing a picture showing a light (airbag?) being moved to a new location, but can't seem to find that thread.
This is as close to a smoking gun as I can find from the There are 2 different HUD install scenario's section of post #1 from this thread: HUD install
"If you use a late 99-04 cluster you will also have to move the airbag warning light located next to the fuel gauge to the location on the Tach or else the light will remain lit al the time."
I suspect that your onto something. If I put a strong light on the original and replacement, I can see the outline of an airbag warning light on both tachs. However, the 99 also has an obvious second identical image slightly left of the fuel gauge, however on the 98 I can't see an airbag warning outline in that location (looks like a blank position). I suspect moving the wire would put the light in the right spot but I'm wondering if it would extinguish it? The DTC message "SDM-NO COMM" indicates that the data link is not getting a response form the SDM. If it was simply a light location issue, it would seem that there would not be a parallel COMM problem and that relocating the light would not extinguish it (however I may also be full of baloney). The tech that looked at the car did not see the SDM module on the TECH2 scanner, makes me wonder if there are 2 issues (light location and a blown SDM), or if the wire location would solve both the light on AND the COMM issue. I don't know enough about these things communicate with the modules to figure it out. I'm going to try to message the guy who did the HUD article to see if he might have some advice.
You probably have a SDM issue as well, but that's separate from the light requiring moving. The SDM issue has nothing to do with the IPC since the IPC is working and connected to the serial bus. Well, you didn't report any other issues so it can apparently communicate with the other modules.
I think you're right Lionel, communication with other modules is OK. Here's what has me scratching my head, the SDM didn't show up on the TECH2, all other modules did. If there was a general data link issue with the new IPC being different, why is the SDM the only module not communicating? My guess - it's busted. If all other modules are communicating, seems to me that the SDM (if functional) would be doing the same. E.G. the light seems to be working, when the car is started the light flashes as normal and remains on that I suspect indicates the SDM is shot or there's some other problem (short to ground, corroded or bad / loose wire). I suspect that if the light were moved it would do the same thing in it's new location. This whole problem is complicated by the fact that the old DIC was out of commission, for all I know, the air bag light may have been on for the last two years!! As a driver, I could honestly care less where the light is as long as the SDM worked. I just hate to go through the hassle and expense of finding a replacement SDM, tearing the car apart to get it in, getting it programmed and finding out it doesn't solve the problem. I'm going to have to break down and fin someone that really trouble shoot the car, I don't have the tools or the knowledge to do so.
+1
Well, I found a 1999 owners manual on the internet. The way the air bag light functions if exactly the same as the 98 except the location of the indicator is not on the tach but next to the fuel gauge. Thus it seems like the cluster is working as designed in spite of the light being in a different location. So for now it seems that the COMM issue is related to either wiring or a failed SDM. I guess that I'm going to have to figure out how to troubleshoot the problem. One thing for sure, like all Corvette issues the solution will be the most miserable, expensive and complicated one possible!!
OK guys, thanks for the input. I'll pull the IPC tonight and switch the bulb locations. Since I'm in there anyway, I'll check the wiring on the SDM, I'll be looking right at it when the radio bezel comes off. I'll keep you posted.
Pulled the IPC and dash and got the bulb moved. Since I already had the dash off the car I decided to go ahead install a HUD since I now have a HUD capable IPC. In speaking with the HUD parts supplier I also asked about the SDM NO COMM message and the light. He said that while C5 IPC's are compatible HOWEVER there were changes in and within model years that have to be accommodated. For example the pin for the light in the 98 and 99 model are different, i.e. the airbag warning light location from 98 to later models. He said while the 99 location in a 98 car may cause the light to be on 100% of the time, it would not cause the communication issue and that I likely have a fried SDM. In addition to the HUD kit he's sending a replacement SDM to try. If it doesn't solve the problem he agreed to take it back for a refund - really great and helpful guy at Vette Nuts!! After I get this thing back together I'll post a followup but my guess is the problem will be resolved by either the bulb move alone or a combo of the bulb move and new SDM.
I want to thank both Lionel and Samas profusely for your help and advice steering me in the right direction to get this fixed. More later.
My final post on this subject. With the dash still torn down I plugged in the IPC, plugged in the SDM, and powered up the car. As I suspected the light is now in the right position, however the airbag remains on 100% of the time. As I suspected, the SDM is shot and not communicating. Ordered a replacement and expect to be back in operation next week with a new HUD and SDM. Thanks to all for your help and advice.
SDM is matched to the PCM some way, by VIN I believe it may be. From what I have read, it gets matched when installed and you can't change the code it matches to again. Is the replacement new or used?
I asked my GM tech about this and he assured me that they are not VIN specific and are essentially plug and play. If it does need programmed he has all the gear to do it with, he makes a living out of adjusting the car's software to improve performance and completely understands the car's comm system. There are some companies out there that claim to be able to reset them if they're activated. This is a whole new kind of problem for me. I learned about working on cars when they had points and distributors and there was no such thing as a computer.
FINAL POST ON THIS SUBJECT - It turned out to be a failed SDM module. I was lucky to find a used SDM with the exact same part and service number. According to a Chevy TSB that someone posted, the BCM checks for the last 4 digits of the part number in order to establish COMM. Apparently my GM Tech and the TSB were right,, the IPC picked up the "used" SDM module with no issue and best of all, the AirBag light flashed 7 times and then extinguished. I had read somewhere else that the BCM will learn the SDM and share the VIN with it. I'm probably talking through my hat on this one but - IT WORKS!!! Thanks to all for the advice on this issue . I also installed a used HUD since I now have a HUD compatible IPC - a nice addition to the car.
98 vs 99 IPC
