Fresh from troubleshooting a seat belt light that (for once) wasn't caused by the SIR/DERM, I decided what I needed was an electronic thingy that I could use to call up all the car's systems by simply selecting them on one gadget. The device would flash the appropriate light on the DIC and have a automatic code clearing routine for the SIR and other devices. It would plug into the ALDL and replace the paper clip approach so near and dear to all of us. (I know that Gordon K. sells something that does the shorting routines but I wanted to build something to do that and also automate the SIR code clearing routine that seems to cause so much trouble due to the precision timing required. I thought maybe I'd make the schematic available to anyone interested if I got it working properly.)

Anyway, to make sure everything was kosher before I started, I used the paper clip method on each system and everything was fine until I got to the SIR system. For that one, I found that when I shorted A to K on the ALDL the Infl Rest light just sits there and doesn't even flash the 12 codes.

Naturally, the big project came to an end pending finding out what's wrong. An FSM is inbound and will arrive sometime in a week or so but I'm wondering if anyone has run into this particular SIR failure mode before? Failing that, what, if anything, does the FSM have to say about a SIR light that comes on and just stares at you when you're trying to recover codes?

Thanks for any enlightenment any of you may have to offer.

Oh -- and yes, I grounded pin K both through pin A on the ALDL and to the negative terminal on the battery just to make sure. No difference.

 

I checked my 1990 FSM.....9J-A-11...."INFL REST" INDICATOR "ON" CONTINUOUSLY. CHART A...
You have 2 choices...you have to disconnect Derm to I/P harness connector..turn ignition on..
1) If lite goes out....check Derm-to-I/P harness connector for short to ground;if OK..replace Derm
2)If lite is "ON"; repair short to ground in CKT 358 (Brown) in I/P harness.
Hope this helps..looks like you have a good one there.
Bill
Pm me your e mail address and I will send you scanned copies..dont know how to post here.

 

Thanks, Bill.

I think this means the DERM is probably toast. Looks like a 1st class B--ch to get to from what documentation I have.

Please use this account for sending the scan imagery: kb9at@fuse.net.

Thanks again.

John

 

Sent!!!

 

John,
The DERM is mounted in front of the CCM, but per the FSM, the connector (10 cavity) is located below the RH side of the Instrument Panel. I'm not sure if it will be behind the tunnel carpet, but it should be easier to get to than the DERM.
CKT 358 will have a Wht/Blk wire in and a Brown wire out of the connector.

 

Thank you that suggestion. Looking at the job involved in getting the DERM out, it seemed to be much more trouble than it was worth. I'll root around and see if I can get to the connector and maybe find out what is going on.

 

Ya can get to the DERM with a Chainsaw I know it's a pain to get to. Good luck with the fix. Pipe

 

Well said, Pipe: Or I could use a little C4 plastic explosive.

I know, bad joke.

All I wanted to do was create a little fixture to help with code retrieval and resetting. As they say -- No good deed goes unpunished.

 

Okay, I have been putting up with this issue for too long. I searched the heck out of this issue and also have a 90 MY. The problem I have is I cannot pull any codes when using either method or to attempt to clear the codes.

Sorry to hijack this old post, but rather than start a new one and seeing this this is the exact problem I have. I am using the Gordon Killebrew plugs as well as the other kit designed by him that actually called ALDL diagnostic grounding tool with the disable switch.

All I get when following the procedure to pull codes or clear is a single flash of the INFL REST lamp and that is it. Not even a code 12, just a single flash.

All the typical work mentioned here and everywhere of cleaning the frame and sensors, etc. was done so many attempts were made to clear the codes, but there are no codes. Just the seat belt light and INFL REST lamps will not go off.

So is the DERM toast if no codes for S.I.R. when following all of the instructions? I can pull codes for anything and everything else with either of Gordon's Killebrews tool kits, just no S.I.R. and cannot find anything about no codes or a single flash.

Thanks in advance.

 

Assuming the Supplemental Inflation Restraint module is receiving power, it's likely toast if it will not disgorge any codes when you short the appropriate pins on the ALDL connector.

It's extremely hard to find salvaged SIR modules for a 1990 Corvette that are guaranteed to work, and as you've read above, it's very hard to remove and replace the module too.

The only other option therefore is to turn off annoying lamps and disable the airbag module.

Remove the offending lamp from the D.I.C to get rid of the INFL lamp (see the FSM for procedure to remove the D.I.C lamp module so you can get to the bulbs) and then move on to eliminating the bogus seat belt light as follows:

You can find the wiring diagram interconnect for the system in the electrical supplement section of the FSM. IF you don't have the electrical supplement to the FSM, there will be a Black wire with a Green tracer (BLK/GRN) going from pin G on the SIR module up to the CCM. This causes the Seat Belt lamp to remain on all the time when there's a problem with the SIR module.

If you've given up on trying to find a salvaged SIR module and you're tired of looking at the seat belt light (but still want the seat belt light to work for its original purpose) you can fish around where passenger side floor carpet meets the carpet that covers the area above the transmission tunnel for a wire bundle coming from the SIR module. There should be some bright yellow wires in the bundle which are a bit fatter than the other wires. These are going out to the acceleration sensors that sense a collision. (Other bundles don't have fatter than normal yellow wires.)

Pull the bundle out so you've got a loop of wire, find the Black/Green wire and cut it. This will interrupt the path from the SIR module to the CCM but will not cause a problem with the CCM nor set any codes.

Next, after making sure the wire ends are not touching each other or anything metal on the wire you cut, put the key in the ignition (without putting on the seat belt) and start the engine. If you cut the right wire, the seat belt lamp will come on initially but will go off when you buckle up. (Mine also will time out eventually even if you don't put the belt on and go out). If that doesn't happen, you've cut the wrong wire and you'll have to splice it back together.

If things work like they should, place some heat shrink on each end of the cut wire or tape each end with electrical tape and then put a tie wrap around the tape so it cannot unwind, fish the bundle back into the space where it was and you're good to go.

Remember, the SIR system is still not going to work and there will likely be no airbag deploy if you have a wreck. All you've accomplished is you've gotten rid of annoying lights - not actually fixed anything.

Since you apparently have a bad SIR module, it would probably be wise to disconnect the airbag module so as to avoid accidental deployment. There are a couple screws on the back side of the steering wheel that you can take loose to gain access to the airbag module. Make certain you disconnect the battery and work from the passenger side so you are not in the line of fire when you are messing with the airbag module!!!!!!

Disconnect the airbag from the harness that feeds it and place a resistor across the connector that comes up through the steering wheel (to avoid setting a trouble code). I do not remember the value of the resistor but it is low - less than 100 ohms as I recall. There is information on this elsewhere on this forum.)

After you have done all of these things, you essentially have a 1989 C4 as far as airbag protection is concerned -- which is to say, no protection at all -- but you have no constant warning lights from then on.

 

I don't know how to thank you for all this information and really do appreciate the time to explain. I was able to get ahold of a Tech 1 and waiting on the module needed to attempt clearing code, knowing it probably won't work since there are no codes. I have decided that there is no way that I want to attempt as you said trying to find a good, used derm even though I found a place that will rebuild the defective derm. I'm not sure I want to go through all of that hassle. I was also wanting to replace the stock steering wheel that I feel is too big and ugly anyway.

Before I remove the airbag/steering wheel I wanted to confirm the impact of getting my car registered here and if that would cause a problem in any of the US states either since I am returning in a few years after this tour in Japan. I know if I return home to Hawaii no issue for safety check as they don't check or care about the airbag. I'm still believe that the original airbag could possible save a life. I can't seem to get this car to pass emissions anyway so I might not need to worry about registering it and just get temp plates as needed when I want to drive it.

You have posted the best information that I have ever seen on what to do if you have a bad derm and options to resolve it another way. Thanks again for taking the time to explain.

 

Before going too far, have you cleaned up the rust around the base of the passenger side sensor? If the ground is lost, the INF RES light will come on. It's common for ground to be lost at this sensor because it sits below the A/C housing and condensation will drip over the sensor and create rust.

The sensor is fairly easy to get to once you remove the rear lower wheel well. It will sit on the frame rail below the A/C housing.

Before removing the sensor, disconnect the battery and wait for about 10 minutes to allow any residual current to drain). The sensor is held in place by two bolts and IIRC, the heads are different size. Remove the harness, remove the sensor and remove all rust from the frame and the sensor mounting bracket. Apply some dielectric grease to the cleaned area and re-install. It might be a good idea to cover the sensor with a piece of rubber sheet to keep condensate off it. A small extra ground wire may help too.

Do the same to the driver side sensor. It's located behind the battery. You have to remove the battery to get to it.

 

I assume you are asking the OP, but I know in my case everything that can be done has been done, minus messing with the DERM. Never had codes but identical problem that is typical in 90 MY in reference to SIR problems.

The best info out there although there is a lot about the grounding issues etc. is right here:

http://www.zr1netregistry.com/Old_Proj/old_proj7.htm

or here:

https://www.corvetteforum.com/techti...D=46&TopicID=2

Thanks for sharing your thoughts on this.