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93 Diagnostic Module Rebuild

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Old 12-16-08, 06:46 PM
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93 Diagnostic Module Rebuild

History: Upon start up, air bag indicator light on left lower panel flashes 10 times indicating an air bag diagnostic module fault. See: 93-4 Body Electric System Manual, Section "S", page 9 for trouble code table.

Cause: There is a internal 1/4 watt 10 amp resistor used as a fuse (marked as such on the circuit board) that disables the module preventing inadvertent deployment of the air bag. One reason for the fuse to blow would be a defective crash sensor (one of 3) in the front end of the car.

Fix: The diagnostic module is no longer carried by Mazda. Prices quoted for non-existent unit ranged from $800 to $1200. A couple of "air bag" module rebuilding outfits quoted prices in the $90 to $120 range and 3 days to a week turn around, "if they could fix it". I figured for that, I would attempt repair myself.

The following is a brief pictorial of the process;
Attached Thumbnails 93 Diagnostic Module Rebuild-1993-mazda-rx-7-air-bag-module-rebuild-015.jpg  
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Old 12-18-08, 04:51 PM
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How does one edit one of their posts? I would like to finish the above.

Thanks.
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Old 12-20-08, 01:09 PM
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Location of Diagnostic Module

The module is not visible in this view; it is located on the tunnel, up under the right side of the dash. You can not miss it, it has a big yellow warning sticker on the case. It is held in place by 3 screws securing the mounting arms of the bracket to the tunnel/chassis. You'll need a stubby Philip head for the lower 2 screws and a regular length for the upper. The screw heads are also 10mm, so a stubby 90 degree head ratchet and deep socket may do the trick here too. You'll either need to be a contortionist or have very small hands to have an easy time getting at this. If you require a bottle of aspirin to get moving in the morning...you'll want to double the dose an hour before attempting removal/installation.

You will need to remove the lower panel under the steering wheel (two screws, one each side) to get to the orange and blue air bag connections under the steering wheel. I have the dash out to repair a blank odometer, so the job looks worse than it is.
Attached Thumbnails 93 Diagnostic Module Rebuild-1993-mazda-rx-7-air-bag-module-rebuild-015.jpg  
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Old 12-20-08, 01:17 PM
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You will need to disconnect the neg. battery terminal to avoid inadvertently discharging the air bag (so says the service manual). Once that is done you can disconnect the orange and blue connectors for the air bag. The terminal slides on to a rack, you can slip it out toward the seat and this will give you better access to the plugs for disengagement. If you leave it on the rack, you may not have enough room to fully push in the release tab for the connection. The orange half on the connector must be removed first, then you can remove the blue connector. The second picture shows the rubber boot that protects where the wires go into the plug. To get full travel on the orange plugs release tab, I had to pull the boot back off the plug.
Attached Thumbnails 93 Diagnostic Module Rebuild-1993-mazda-rx-7-air-bag-module-rebuild-014.jpg   93 Diagnostic Module Rebuild-1993-mazda-rx-7-air-bag-module-rebuild-013.jpg  
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Old 12-20-08, 01:19 PM
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The Diagnostic Module is mounted with the 3 screws here...
Attached Thumbnails 93 Diagnostic Module Rebuild-1993-mazda-rx-7-air-bag-module-rebuild-012.jpg  
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Old 12-20-08, 01:25 PM
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The Module has two plugs going into it. You will see what appears to be a release tab on each plug...they ain't. Instead, use your finger nail to pull and lift out these odd locking "combs" (for lack of a better name). Once you have lifted out these locks you can then pull out the plugs.
Attached Thumbnails 93 Diagnostic Module Rebuild-1993-mazda-rx-7-air-bag-module-rebuild-009.jpg   93 Diagnostic Module Rebuild-1993-mazda-rx-7-air-bag-module-rebuild-010.jpg  

Last edited by IMZman; 12-20-08 at 01:27 PM.
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Old 12-20-08, 01:32 PM
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Here is the module after removal. The plastic lid just snaps on to the mounting chassis. You can remove it using your fingernails or a small thin blade screwdriver at the tab/slot points around the case.
Attached Thumbnails 93 Diagnostic Module Rebuild-1993-mazda-rx-7-air-bag-module-rebuild-007.jpg  
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Old 12-20-08, 01:34 PM
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BE CAREFUL when REMOVING THE BLACK COVER as the circuit board inside IS FREE TO FALL OUT once the cover is removed. The circuit board just sits in the mounting bracket.
Attached Thumbnails 93 Diagnostic Module Rebuild-1993-mazda-rx-7-air-bag-module-rebuild-006.jpg  

Last edited by IMZman; 12-20-08 at 01:36 PM.
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Old 12-20-08, 01:38 PM
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Lift the circuit board off the mounting chassis and you are ready to get to work!
Attached Thumbnails 93 Diagnostic Module Rebuild-1993-mazda-rx-7-air-bag-module-rebuild-005.jpg  
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Old 12-20-08, 01:45 PM
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Just ahead of the tip of the screwdriver is the 1/4w 10 amp resistor that is the "fuse". It is the blue capsule shaped component with several stripes. Just to the left and slightly lower than the left leg of the resistor you will see "Fuse 1" imprinted on the board. The service manual also says that there is a "Battery backup" in this module. I could not find one. If you know where it is hiding...let me in on the secret.
Attached Thumbnails 93 Diagnostic Module Rebuild-1993-mazda-rx-7-air-bag-module-rebuild-001.jpg  
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Old 12-20-08, 01:54 PM
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Mark the position of the resistor with your finger and turn the board over and find the two legs coming through the board. Use a desoldering iron (my preference) or soldering wick to remove the solder. Remove the old resistor and put the new one in and solder it in place using .022" dia. solder. While you are there, carefully check the other components for any obvious signs of damage...mainly the 10 "can" capacitors for any leakage of electrolyte or bulging. Look for any black sooty like deposits around the capacitors base...or any oily/shiny looking liquid. Replace anything that is suspect. You can plug the module back into the harness without mounting it on the tunnel to check your work.

Assembly is the reverse order of steps.

Total time for removal/repair/replacement is 2.5 hours or less. Resistor cost .17 cents each, so get a few. Remember to check the resistance of the 3 "D" crash sensors at usually one of these is bad and that is what trips the fuse. Fix this problem before reinstalling the Diagnostic module.
Attached Thumbnails 93 Diagnostic Module Rebuild-1993-mazda-rx-7-air-bag-module-rebuild-003.jpg  

Last edited by IMZman; 12-20-08 at 02:00 PM.
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Old 12-21-08, 10:01 AM
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Great post!

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Old 01-11-09, 07:12 PM
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As an after thought, I figured I would go ahead and list the other larger capacitors on the board that may cause problems. If the 1/4w resistor fuse blows and/or you perform the service manual troubleshooting steps for your warning code and they check out good...the manual says, "replace diagnostic module"...well, they are not available anymore...and the main cause for the fuse to blow if there is not a "problem" detected in the troubleshooting steps for your trouble code...is the six 1800uF 25v caps in the middle of the board.

The electrolytic cap's have a life span of around 15 years so it's probably a good idea to just replace them while you have the unit out anyway.

There are two Nichicon series cap's that are of the same size as the OEM's the VR series (long life) and the PW series (high reliability). The PW's are meant for switching circuits which are really hard on cap's...the PW series life is not as long and they cost twice (78 cents vs. 36) what the VR series does. The OEM Nichi LXF series cap's are the older version of the PW...so I figured I'd spend the few pennies more to get them...I mean, it's a air bag diagnostic unit...I want it to have "high reliability" right?

Here are not all, but the major players on the circuit board likely to cause trouble:

1) Six 1800uF 25v; DigiKey #493-1836-ND (Nichicon #UPW1E182MHD6) .78 cents each.
2) One 1000uF 25v: DigiKey #493-1305-ND (Nichicon #UVZ1E102MPD) .52 cents each.
3) Three 47uF 16v: DigiKey # 493-1775-ND (Nichicon #UPW1C470MDD) .26 cents each.

In addition to the 1/4w 10 ohm resistor (fuse) previously listed; there are two 1/2w 42 ohm resistors on the board also, but there should be little need to replace those unless obviously burnt or broken.
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Old 01-29-09, 02:15 PM
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Great writeup! Thanks for sharing. My airbag computer spontaneously died and started flashing code 10 while the car was sitting in storage....I figured it was a capacitor, but couldn't get one of the connectors unplugged to get the module out to open it up and see.

Also of note, this computer may actually be from the Ford parts bin. I saw some documentation online for a Ford airbag computer which had the same exact codes as our computer.

You said you found no backup battery....might that be the purpose of all those capacitors?

One other thing...I don't know if this is possible, but can you go back and edit the title of the thread to include "Airbag" so it will be more easily found on searches?
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Old 01-29-09, 04:42 PM
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If you are talking about the white and yellow connectors going into the module...they are a PITA. Just keep squeezing and take your time. I gave it a break and tried again and the damn thing just about fell out. Go figure.

Being that Ford and Mazda are in bed together it would not surprise me if they swapped stuff back and forth. More than likely though, those codes are a "standard", but I am just guessing.

I would not think they would use the terminology of "Battery" for cap's...but then they are grouped together in a battery...so maybe that is it. Usually, cap's working like that are for some low draw thing like RAM...but I am electronically challenged and just make up stuff as I go alone...until someone tells me different.

And unfortunately, I can not amend the title. After 30 minutes what you post is locked. In my warped way of thinking, I named it thus to separate it form "air bag" posts that had nothing to do with the Diagnostic Module...maybe not such a hot idea after all. Maybe a Moderator can add "Air Bag...", if not maybe I can cut and paste it to a new thread with a better title.
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Old 01-29-09, 09:20 PM
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Originally Posted by IMZman View Post
If you are talking about the white and yellow connectors going into the module...they are a PITA. Just keep squeezing and take your time. I gave it a break and tried again and the damn thing just about fell out. Go figure.
Yeah...those are the ones I'm talking about. Do they both have the "combs" you pictured? I got one of the connectors out without pulling the "comb" out.

I would not think they would use the terminology of "Battery" for cap's...but then they are grouped together in a battery...so maybe that is it. Usually, cap's working like that are for some low draw thing like RAM...but I am electronically challenged and just make up stuff as I go alone...until someone tells me different.
The only reason I can see for having a "battery" backup in this module is to pop the airbags in case power gets cut in a crash. In that scenario the bags would likely need to deploy a fraction of a second after the power is lost. Since power is only needed for a few seconds, capacitors would seem to be the logical choice.
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Old 01-30-09, 08:23 AM
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Yes, both connectors should have the comb clips unless previously removed/lost. I cannot remember, but there may be another small release tab on the side of the connector you can not see, check the one you removed. I am thinking there was only the one release tab (after removing comb).

You very well could be correct about the capacitors. Like I said, I am not very mechanical...and am down right ignorant about electrons. After 7 years of ownership, it can tear down and rebuild Russian motorcycles in my sleep. To further my education, I am now plunging into the other side of the technology spectrum by tearing apart a RX-7. A lot cheaper and quicker than paying to go to school to learn this stuff...plus...classes run on my schedule
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Old 05-06-09, 05:23 PM
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Airbag Diagnostic Module

Thanks Bill.

My Airbag Diagnostic Module is blinking at me 3-times, and the flowchart analysis, is saying: replace module if all other test are good.

FWIW, here's the Digikey PN# for the resistor/fuse:

10.0XBK-ND

:-) neil
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Old 05-23-09, 12:13 PM
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Also, it is a 1/4-watt metal-film 10-ohm resistor, not a "10-amp" resistor.

:-) neil
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Old 05-24-09, 08:04 AM
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I replaced all the electrolytic caps, and the "fuse" resistor.

I still get "3-blinks".

I measured ALL the "silver" diodes (I think they are zener) and I'm getting an "open circuit" when measured both ways, which supposedly means they are "open".

I'm using a Fluke 79 DMM set to the "diode" setting.

The green banded diodes are "open" one way, and I do get a resistance of about 250-ohms the other way.

Am I doing something wrong ?

Can it be that all of the diodes are bad ? Seems unlikely. . .

If I do have to replace them, what's the specs. Only markings are the silver band and a "4", rotate the diode, and then either a "D" or a "O".

They about the size of the 1/4-watt resistor "fuse".

Anyone know the transistor pn#s ?

Thanks,
:-) neil

http://www.elexp.com/t_test.htm
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Old 12-06-11, 12:39 PM
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If the Fluke DMM uses a low internal voltage to test, it probably won't reach the 0.6 volts or so required to forward-bias a silicon diode. So the 250 ohms in one direction, open in the other, probably indicates a good diode.

(Thread resurrected as a result of linking from another, current, post.)
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Old 01-09-12, 10:12 AM
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Wow!! Great Post... i have the 10 times flashes...
i will read this now and i hope i can fix the problem

Thanks a lot
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Old 12-20-12, 11:57 PM
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Does anybody know if this fix is valid for a 1991 model? My wheels rubbed on the airbag wiring and ripped it out of the crash sensor. The car now refuses to start even after reconnecting the sensor. It keeps blowing a fuse in the bay. The fuse closest to the engine on the drivers side of the bay. Anybody have advice?
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Old 12-21-12, 04:23 PM
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good post i dont have this problem but i will have a reference incase
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Old 06-30-13, 03:06 PM
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is there any little trick to get the two plugs of the unit, I got those pop out tabs out, but my connecters do not want to come out, I have the unit unbolted from the car.
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