DERM Question - '90
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Instructor
Joined: May 2009
Posts: 118
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From: Alexandria Kentucky
DERM Question - '90
The DERM module in my 90 has crapped out. The INFL REST Light is on all the time which is normal when there is a problem but this one will not display codes so it's fried. You cannot buy a new one from GM so I'm going to disable the airbag and then cut the Seat Belt and Infl Rest light driver wires coming from the unit. (I can't just unplug the cable coming from the unit because there is a power lead that loops through the unit to the ECM so I have to leave the DERM in place with the connector plugged in.)
The FSM has a rather involved procedure to get to the DERM but it assumes you are going to remove the unit and put a replacement in its place which I'm not.
So here's the deal: On the drivers side, the large, carpeted trim piece that runs along the transmission tunnel has a small door at the top which is there to allow removal of some hardware on the left side of the DERM. You have to remove the driver's side knee bolster to get to it but otherwise it seems like a relatively easy job. Does anyone know if you can reach the 8 pin connector that comes out of the DERM from that door? If you can, it would greatly simplify what I intend to do.
Thanks for any advice.
The FSM has a rather involved procedure to get to the DERM but it assumes you are going to remove the unit and put a replacement in its place which I'm not.
So here's the deal: On the drivers side, the large, carpeted trim piece that runs along the transmission tunnel has a small door at the top which is there to allow removal of some hardware on the left side of the DERM. You have to remove the driver's side knee bolster to get to it but otherwise it seems like a relatively easy job. Does anyone know if you can reach the 8 pin connector that comes out of the DERM from that door? If you can, it would greatly simplify what I intend to do.
Thanks for any advice.
Team Owner
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I believe that a 2 ohm resistor would "turn-off" the "INFL REST" light. I would think you could accomplish this at a couple different locations:
1. Top of the column at the connector for the "Airbag"
2. Base of column where the column harness connects to the "pigtail" from the DERM.
I've not done this but I don't know why this wouldn't accomplish what you want to do with very little "aggravation"!!!
1. Top of the column at the connector for the "Airbag"
2. Base of column where the column harness connects to the "pigtail" from the DERM.
I've not done this but I don't know why this wouldn't accomplish what you want to do with very little "aggravation"!!!
Thread Starter
Instructor
Joined: May 2009
Posts: 118
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From: Alexandria Kentucky
A 2 ohm resistor simulates the load that the DERM sees when looking into the airbag deployment squib. If you pull either connector to the airbag and don't simulate the load, the INFL REST light will be lighted and code 35 will be set, indicating an open circuit at the Inflator Squib. If someone wants to disable the airbag in a working system, you're exactly right, you have to simulate the load and the 2 ohm resistor is the way to do it. Since my DERM is fried (if won't even display code 12 -- the INFL REST light never goes off, even in the test mode) I don't believe this will work for me. That said, I still want to thank you. At least you tried to help.
Safety Car
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From: Yucaipa CA
Thread Starter
Instructor
Joined: May 2009
Posts: 118
Likes: 16
From: Alexandria Kentucky
I am pretty sure that there is only one P/N for the 90 DERM. I don't have a parts catalog though so I'll have to wait until Monday to call the Chevy Dealer and ask if 1228874 is the right P/N. It isn't listed on GM Parts Direct anymore.
I appreciate the offer to let me test it for free. Is the price $150 if I want it?
I appreciate the offer to let me test it for free. Is the price $150 if I want it?
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Team Owner
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'90 MY DERM is a single year application and also Corvette only. GM part # 10094618 I believe.
The Craigs List link is for sure a '90 MY DERM and the $150 ask is a deal "if it's infact functional".
I have one but I paid substantially more, much more for mine than the $150 ask.
I don't have all of the correct service manuals but if you're just attempting to "pass the power" thorough the DERM to satisfy the ECM maybe sustituting the 1228874 which also fit '91 MY and "early" - '92 MY Corvettes but many other GM lines might be "the ticket". If the connector wasn't a "dead on" match maybe you could just do a "pin-out" swap to the correct mating adapter. I would I think rely on a '91 MY FSM
The 1228874 should be available from many/many salvage yards and you could make sure it was removed from a car with "no deployment". The "free test" offer is generous from "jeff1167".
Curious! What does the ECM want to or need to see from the DERM?
The Craigs List link is for sure a '90 MY DERM and the $150 ask is a deal "if it's infact functional".
I have one but I paid substantially more, much more for mine than the $150 ask.
I don't have all of the correct service manuals but if you're just attempting to "pass the power" thorough the DERM to satisfy the ECM maybe sustituting the 1228874 which also fit '91 MY and "early" - '92 MY Corvettes but many other GM lines might be "the ticket". If the connector wasn't a "dead on" match maybe you could just do a "pin-out" swap to the correct mating adapter. I would I think rely on a '91 MY FSM
The 1228874 should be available from many/many salvage yards and you could make sure it was removed from a car with "no deployment". The "free test" offer is generous from "jeff1167".
Curious! What does the ECM want to or need to see from the DERM?
Last edited by WVZR-1; Jun 28, 2009 at 01:30 PM.
Thread Starter
Instructor
Joined: May 2009
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From: Alexandria Kentucky
Thanks WVZR-1 for the insight. It helps a bunch.
I could simply jumper around the the problem if I had to but if I clip the INFL REST and Seat Belt lamp feeds plus disable the airbag, I don't have to go through all the heartache and sorrow involved with removing the actual DERM. Of course, if I can buy a working module and keep the car's systems in place, I'd much rather do that in spite of having to tear the dash apart.
As for the DERM and ECM, +12 comes from the ignition switch to the DERM, through a 10 amp fuse. Once at the DERM connector, it loops right back out to the ECM through a 3 amp fuse. From the schematic, the DERM's electronics never "see" anything but the feed from the 10 amp fuse.
The loop through goes to the Ignition feed input for the ECM. I'd guess GM didn't want people operating the car with the DERM removed -- probably for liability reasons -- so they did this looping deal just to make sure. (They are obviously paranoid about this system, else why light both the INFL REST light AND the Seat Belt light when there is a problem. I'm surprised they didn't disable the ignition too.)
I could simply jumper around the the problem if I had to but if I clip the INFL REST and Seat Belt lamp feeds plus disable the airbag, I don't have to go through all the heartache and sorrow involved with removing the actual DERM. Of course, if I can buy a working module and keep the car's systems in place, I'd much rather do that in spite of having to tear the dash apart.
As for the DERM and ECM, +12 comes from the ignition switch to the DERM, through a 10 amp fuse. Once at the DERM connector, it loops right back out to the ECM through a 3 amp fuse. From the schematic, the DERM's electronics never "see" anything but the feed from the 10 amp fuse.
The loop through goes to the Ignition feed input for the ECM. I'd guess GM didn't want people operating the car with the DERM removed -- probably for liability reasons -- so they did this looping deal just to make sure. (They are obviously paranoid about this system, else why light both the INFL REST light AND the Seat Belt light when there is a problem. I'm surprised they didn't disable the ignition too.)
Last edited by C4-90-41001; Jun 28, 2009 at 10:50 AM.
Team Owner
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I have I'm quite sure ID'd the service 10-pin male and female connectors (female on the DERM and male to the chassis). GM ID's male and female from the termminal gender NOT the connecting gender.
Drop me a PM and with an email and I'll send you the information. You could construct a pigtail I would think from the 122874 to the male chassis connector using these.
The 10-pin (only 8 populated) is on a pigtail 16" long that exits the DERM with the pigtails that go to both the front impact sensors!
I've had a 128874 in my hands and it quite compact vs the original. It's an aluminum box similar in size to the radio CDM. You could likely "stuff it" somewhere!!
PM me your email!!
Drop me a PM and with an email and I'll send you the information. You could construct a pigtail I would think from the 122874 to the male chassis connector using these.
The 10-pin (only 8 populated) is on a pigtail 16" long that exits the DERM with the pigtails that go to both the front impact sensors!
I've had a 128874 in my hands and it quite compact vs the original. It's an aluminum box similar in size to the radio CDM. You could likely "stuff it" somewhere!!
PM me your email!!
Thread Starter
Instructor
Joined: May 2009
Posts: 118
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From: Alexandria Kentucky
Jeff:
I was able to make contact with the guy on Craig's list you told me about and bought his DERM. Looks like I've got a fun filled weekend end ahead of me ripping the dash apart.
Thank you very much for the assist!
John
I was able to make contact with the guy on Craig's list you told me about and bought his DERM. Looks like I've got a fun filled weekend end ahead of me ripping the dash apart.
Thank you very much for the assist!
John
Safety Car
Joined: Oct 2008
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From: Yucaipa CA
I've got the air bag light on my 90 all the time as well so this is something I have to look into as well, heard it's common on the 90's. I'm going to try re-grounding my sensors though and see if that fixes mine.
Thread Starter
Instructor
Joined: May 2009
Posts: 118
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From: Alexandria Kentucky
That's only true for units that are displaying sensor codes. My unit will not display any codes, not even the "12" code which is a delimiter that is sent even if nothing is wrong.
My DERM is defective because the diagnostic function will not work.
Thanks for trying to save me from doing something wrong but if the DERM will not produce even the "12" code, it is definitely bad.
John
My DERM is defective because the diagnostic function will not work.
Thanks for trying to save me from doing something wrong but if the DERM will not produce even the "12" code, it is definitely bad.
John
Burning Brakes
Joined: Jul 2005
Posts: 1,147
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From: Motor City area Michigan
A friend has a car with the light on. It has not been a regular driver so doubt that the ground is the issue, but who knows. Can you also do the entire job? We are in the Detroit area.
Advanced
Joined: Dec 2008
Posts: 66
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From: Okemos Michigan
Fixing the DERM
Greendot,
My fault for implying that I was the one to fix a bad DERM. I sent mine to a place in Texas. Its been a while so I need to look up my papers of who I sent the DERM to. The cost was $150 I remember. If you want to give me an email, I can send you the information over this weekend??
John White
My fault for implying that I was the one to fix a bad DERM. I sent mine to a place in Texas. Its been a while so I need to look up my papers of who I sent the DERM to. The cost was $150 I remember. If you want to give me an email, I can send you the information over this weekend??
John White
Burning Brakes
Joined: Jul 2005
Posts: 1,147
Likes: 7
From: Motor City area Michigan
I have sent you an email so you can reply to that. Thanks
Hope the price is still the same. Internet search did not show the TX place, but a PA place that wants $795 to repair!!!
Hope the price is still the same. Internet search did not show the TX place, but a PA place that wants $795 to repair!!!