Airbag Diagnostic Module

[GRWeldon]

Anybody have a picture of one of these things? It's supposedly to the right of the glovebox under the dash. I've got a parts car disassembled in that area but I don't exactly know what this looks like. The drawing shows a rectangular box with rounded corners mounted to a bracket. I can't seem to find anything that looks like that.

Got an airbag code 51 on my SC...

 

[XR7-4.6]

Blue box

 

[Derphound01]

51 is usually caused by a short to ground for a circuit in the airbag system that would normally throw a 13 or 14 DTC. It can result in a bricked module. Disconnect the battery and then check the grounds and connections on that side before you replace the module.

If you have a short elsewhere, you'll just keep bricking them until it is fixed.

 

[Derphound01]

OH. Big thing to remember. Do not use a power probe or meter while testing airbag circuits unless you want to blow an airbag.

Feel free to guess how I learned this.

 

[GRWeldon]

Blue box

Thanks for the pic. I'm assuming that is the passenger side wall under the glove box. Ever seen one that was black?

Also, is this visible on top or do you have to remove other devices and dig for it? I have an LX parts car disassembled very heavily in that area and I can't seem to find a blue box. I have however found this:

Edit: I found the blue box in my parts car. I'd still like to know what the black box is if anybody knows. It came from the same general area under the glove box...

 

[GRWeldon]

51 is usually caused by a short to ground for a circuit in the airbag system that would normally throw a 13 or 14 DTC. It can result in a bricked module. Disconnect the battery and then check the grounds and connections on that side before you replace the module.

If you have a short elsewhere, you'll just keep bricking them until it is fixed.

Thanks for the very helpful reply. I'm a bit short in the knowledge department with automotive electrical diagnostics. I know generally about what you are telling me about grounds, but if you can, could you be more specific on what to check?

I mean are you talking engine strap grounding? Battery terminal grounds? Other ground wires that might be located elsewhere or are you talking broken/bare insulation on wires, etc.?

 

[Derphound01]

It really could be any of the above. Most likely broken or bare wires, but it could also be a clockspring, a connector, or many other things. You are likely best off finding the EVTM for your model year. That will have the steps needed.

The Ford truck forums have a lot of info on airbag faults. Here's some that may help:

1994 F150- airbag code 13, already replaced clockspring... - Ford Truck Enthusiasts Forums

1987 - 1996 F150 & Larger F-Series Trucks - 1994 F150- airbag code 13, already replaced clockspring... - I have a 1994 F150 with airbag code 13. I've already replaced clockspring. I've read the code is for a short, but are there any particular areas I should be looking? Thanks

www.ford-trucks.com

Airbag code 14 - Ford Truck Enthusiasts Forums

1978 - 1996 Big Bronco - Airbag code 14 - Hey everyone, was overseas for 2 1/2 years and very busy since I got home. Bronco was in storage for quite sometime. Got home in time to go deer hunting. After hitting a very deep pothole the airbag light started flashing. It went out not long after and...

www.ford-trucks.com

 

[jco1385]

Here are the airbag pages from the 1994 EVTM (looks like you have a 1994 SC). There is a diagnostic section in the service manual (01-20B) as well. That section is 68 pages. Let me know if you need that and I can get it to you.

 

[XR7-4.6]

Thanks for the pic. I'm assuming that is the passenger side wall under the glove box. Ever seen one that was black?

Also, is this visible on top or do you have to remove other devices and dig for it? I have an LX parts car disassembled very heavily in that area and I can't seem to find a blue box. I have however found this:

Edit: I found the blue box in my parts car. I'd still like to know what the black box is if anybody knows. It came from the same general area under the glove box...

What you have pictured is the PWM for the blower motor, which mounts behind the glove box as well but on the heater box directly behind.

 

[GRWeldon]

What you have pictured is the PWM for the blower motor, which mounts behind the glove box as well but on the heater box directly behind.

Thank you sir. You are a wealth of information! How long have you been working on Cougars/Tbirds? I've been driving them for 20+ years. Working on them on and off the whole time but have been majorly working on them for just less than a year. I had two and wanted to get them in good running condition. Then I found out that some parts are scarce. Now I have 7!

 

[GRWeldon]

Here are the airbag pages from the 1994 EVTM (looks like you have a 1994 SC). There is a diagnostic section in the service manual (01-20B) as well. That section is 68 pages. Let me know if you need that and I can get it to you.
View attachment 6775

Thank you...all that is great but as I mentioned previously, I'm weak in electrical diagnostics. I'm not sure what to do with those diagrams. BUT, I'll take anything you wish to give me. I do have a 94SC. Also a 94V6, a 95V8 Cougar, two 96V8s Birds, a 96V6 Bird and a 97V8 Cougar. I would imagine they are all about the same?

 

[White Lincoln]

OH. Big thing to remember. Do not use a power probe or meter while testing airbag circuits unless you want to blow an airbag.

Feel free to guess how I learned this.

Um... (guessing here)... You tried testing this on your neighbors car, right?

 

[Derphound01]

Actually was a customer's car. Was borrowing a power probe from someone else because mine was broken. It was one I'd never used before and I didn't have it set right.

 

[jco1385]

All of those vehicles would share the same airbag system, if that's what you're asking.

 

[White Lincoln]

Actually was a customer's car. Was borrowing a power probe from someone else because mine was broken. It was one I'd never used before and I didn't have it set right.

Yikes! That must of sucked for you to have to buy a new air bag for someone else.

 

[GRWeldon]

All of those vehicles would share the same airbag system, if that's what you're asking.

I was and that's what I figured.

 

[jco1385]

Here is a link to download Section 01-20B Restraints, Passive - Supplemental Air Bag System from the 1994 factory service manual.

Link -> 1994 Thunderbird Air Bag System

 

[XR7-4.6]

Thank you sir. You are a wealth of information! How long have you been working on Cougars/Tbirds? I've been driving them for 20+ years. Working on them on and off the whole time but have been majorly working on them for just less than a year. I had two and wanted to get them in good running condition. Then I found out that some parts are scarce. Now I have 7!

Geez probably close to 20 years as well. I’ve been lucky since there were quite a few local Tbird/cougar owners I’ve known I’ve helped/helped me to really inundate myself in these cars in that time. I’ve only ever owned my one Cougar but by stink is on a few MN12s out there in the region lol

I also spent an inordinate amount of time in the junkyard finding all the nuances between years/options. Back when you could find these cars in this region there still.

 

[Grog6]

The air bag box is deliberately killed,under certain circumstances.There's a thermal fuse inside it, that has a fucking resistor glued to it with thermal epoxy. Under certain conditions, it turns the resistor on, blowing the fuse. Bastards! Replacing the thermal fuse can fix the box, depending on the error.It's not the dinky troubleshooting light that blows the airbag; it's the static electricity on you that pops the bag. That's why I don't fuck with rocket fuel or fireworks mixes in the winter, lol. It sucks watching your whole work area suddenly clear, and your ears ringing, as you pick your dumb ass off the floor in the shed, lol. Static is a bitch, and you only have to move a few electrons around to set it off.
By contrast, deliberately blowing the detonator in the airbag,as the module does in a wreck, takes a cap of a certain size charged to 400v and a special circuit to set off.
On the good side, if you have one of the exploding takata airbags, I've heard they're a lot harder to set off with static. But you may eat shrapnel.

 

[Kidd-7]

the break down voltage for air is ~2000v / square inch.

 

[GRWeldon]

Here is a link to download Section 01-20B Restraints, Passive - Supplemental Air Bag System from the 1994 factory service manual.

Link -> 1994 Thunderbird Air Bag System

Thank you JCO for the document. Regarding my airbag code 51 without an accompanying code 13 or 14, here's what I believe might have happened to my car:

From what I gather, the Airbag Diagnostic Module (ADM) is constantly checking for forces that might set off the airbag. Since the airbag is only supposed to deploy when the front of the car collides with an object laterally, if the ADM senses a force great enough in a direction that isn't lateral, say up/down or side-to-side, it blows the circuit fuse to keep the airbag from deploying when it wouldn't be appropriate.

I'm proposing this because it fits what happened to my SC. I drove perpendicularly into a deep rut that was hidden by tall grass. The core support took a hit hard enough to bend it and I believe it cracked the AC accumulator. I believe this force was what caused the ADM to blow it's fuse to keep the airbag from blowing when it wouldn't be appropriate.

I can not find any poor grounding situation or bad wiring or corroded terminals and I'm thinking it should be safe to install another ADM without it blowing the fuse.

Sound reasonable?

 

[GRWeldon]

Nobody have an opinion on whether my scenario above could be possible? I'm trying to decide whether or not I will kill another airbag module if I install a different one. I do have two, but I really don't want to kill any if possible...

 

[Derphound01]

It is definitely possible. No way to confirm it without risking another module though. Looking at the wiring diagrams, you could have a bad Safing Sensor. That will blow the thermal fuse if it gets stuck in the "closed" position. So yes, your theory is plausible. See Page 01-20B-12 of jco1385's link.

A note though, our airbag systems aren't advanced enough to detect G-forces for deployment purposes alone. The system is only triggered by the crush sensor getting crushed on the front of the car. Those sensors are wired directly to the airbags which in turn trigger the ignitors to blow the airbags when a crash is substantial enough to crush the sensors. The airbag module in our cars is just a diagnostic module and doesn't actually control whether or not the bags deploy.

There is a Safing Sensor (G-force based) but its only job is to make sure the impact is strong enough to warrant inflation should the impact sensors get crushed. So in theory you could crush the impact sensors and still not have a deployment if the G-forces don't warrant it.

The airbag module in our cars is just a diagnostic module and doesn't actually control whether or not the bags deploy. The thermal fuse blows when a fault exists that could cause unwanted deployment of the airbags i.e.: a short between the sensors and ignitors or a bad Safing Sensor.

 

[KevinVarnes]

I'm not sure. I found this on a Ford truck forum:

NOTE:
The diagnostic monitor contains an internal thermal fuse that is not serviceable. The thermal fuse is controlled by a computer inside the diagnostic monitor. The computer will blow the thermal fuse whenever a short on the deployment circuits occurs. The thermal fuse does not blow because of excessive current flowing through it. DO NOT attempt to jumper out the thermal fuse with a circuit breaker or any other type of fuse.

NOTE:
DO NOT install a new diagnostic monitor until the short has been located and corrected. If a short to ground has not been located and corrected, then the short to ground is intermittent and IS NOT PRESENT AT THIS TIME. Installing a new diagnostic monitor with an intermittent short in the system will result in blown diagnostic monitors and repeat repairs.

The diagnostic monitor measures the voltages at the diagnostic monitor connector pins. When certain air bag deployment wires are shorted to ground (heavy lines illustrated in the schematic below), the system may become susceptible to unwanted deployment of the air bag(s). The diagnostic monitor senses a short to ground on any of these circuits and helps prevent unwanted air bag deployant by blowing the diagnostic monitor thermal fuse. Blowing this fuse removes all power (battery and back-up power) from the air bag deployment circuits. While the short to ground exists, the monitor will flash fault code 13. If the short to ground is intermittent and temporarily corrects itself, the diagnostic monitor will flash code 51.

NOTE:
If the short to ground returns, the high priority code 13 will flash instead of 51.

If the air bag lamp is flashing code 51 and a short to ground has not been serviced, this means that an intermittent short to ground exists in the air bag system. The diagnostic monitor should be replaced only after repairs to the intermittent short have been completed.

It sounds like you could still have a short to ground.


FYI, This is a link to the thread I was reading. It sounds like a guy was able to successfully repair the thermal fuse and there are details in there on that.

Can I Rapair The Air Bag Module? - Ford Truck Enthusiasts Forums

Aerostar - Can I Rapair The Air Bag Module? - Hello, my 1993 4.0 Lt ,6cil XLT has the 51 code light turned on. I check the code list and it means that the air bag Diagnostic Monitor (blue box under the dash) has a fuse open . Can it be repair for an expert? or I need a new Air Bag Diagnostic...

www.ford-trucks.com

 

[dDUBb]

No such thing as a crush sensor. They are impact sensors and require two sensors to deploy the airbags. Recall the scene from Fight Club where they take two baseball bats to blow the bags.

 

[Grog6]

The impact sensor is by the outside temp sensor. The safing sensor is in the drivers kickpanel. If you trier te front sensor, and stomp your foot, the airbag blows.

 

[GRWeldon]

The impact sensor is by the outside temp sensor. The safing sensor is in the drivers kickpanel. If you trier te front sensor, and stomp your foot, the airbag blows.

There was a typo in there... "If you TRIER TE front sensor..." What was that supposed to mean?

Also, I haven't checked out the "safing sensor". Should I disassemble the driver's kick panel. Is this something I should do just to take a look?

I'm not really sure where I should be checking for poor grounds...

 

[dDUBb]

Trip The

 

[GRWeldon]

I hate to continue to bother y'all because of my ignorance but you guys (are there any gals here?) are the best source of info I've found when it comes to our cars.

Continuing on with the Airbag code 51 and searching for shorts... I'm doing the best I can to follow the wires from the crash sensors. Haven't looked much yet on the passenger side but on the driver's side the wires for the crash sensor go in to a larger harness that all sorts of things are connected to, such as: The horns, the windshield washer pump and level sensor, both the pulling and pushing fan (this is on my SC remember) and it looks like maybe the fog lamps.

In previous testing I noticed that only one horn was working. Today I removed them and tested both, confirming that one wasn't working and grabbed one from a parts car and tested it before installing on the SC. Would this be the kind of thing I'm looking for? I checked the non-working horn and when placing the probes on the terminals testing ohms, they showed continuity. The good one read about 78K ohms. I don't know if this is the type of thing I'm looking for or not. I'm a bit concerned about my cooling fans. I have removed them both and tested them with a 12V source and they work, but they don't come on when the car starts to rise above normal operating temperature. I'm really not sure where to go with that. Any instruction volunteered would be much appreciated.

I haven't checked anything inside yet because the car is on the lift waiting for me to bleed the brakes after replacing a rear caliper and pads. I've been a bit under the weather and haven't quite gotten around to finishing the job I started last week. Do I really need to worry about the "safing" sensor? My airbags have not deployed and I have no reason to believe there are any shorts under the driver's kick panel. All of the minor damage is in the front of the car where I went off the road swerving to miss a tree in the road around a corner at night on my way to work ten years ago.

It also appeared that the same harness the crash sensor comes out of also has branches for the ABS. I need to check but I was under the impression with the ignition on, the ABS light should come on for a few seconds, then go off...indicating the ABS was working. Is this the case?

I sincerely thank any of you for any useful replies that you may post. I don't know where I'd be in my reconditioning endeavors without this group of knowledgeable folks!

 

[dDUBb]