Flashing airbag code 51 on '93 Grand Marquis

[Mealticket]

All - when I bought this car it already had a bit of body damage on the drivers' side front near the marker lights. I understand that code 51 indicates a short to ground. I need some pointers on where to start to look for the short. I'm pretty sure it's not the clockspring since the horn works. Also would like to know if the sensors are near the top of radiator support under the plastic flaps. I pulled up those two flaps and looked in and I see units that I suspect are the sensors but can't seem to verify. I also see a silver module of some sort underneath the plastic cover near the middle; is this part of the airbag system? Am planning a trip to Pick N' Pull to rip one of these apart but in the meantime wanted to ask. Thanks,

[sly]

51 Diagnostic Monitor Internal Thermal Fuse - Blown and Short to Ground No Longer Exists

The internal fuse of the airbag module is blown. You will need the module (blue box with wires coming out of it behind the glove box). Or repair it with another thermal fuse like I did my old one (that's sitting on a shelf) that had the same issue. You should check the wires in the damaged area to make sure there's not any with broken/cracked/chaffed insulation before changing out/repairing the module so the problem doesn't come back.

[Mealticket]

Thanks, Sly. I'm on it. I will be at a yard today and will scope out a '92 and two '95s because that's what they have right now. I'll take down the P/Ns on the blue box and then come back and check mine. Found a uTube video and it seems fairly easy to check continuity on that fuse,

Mealticket

[sly]

the 92 should work (especially if it's a later production version) as well as the 95s, not quite sure about the 95s though. If they have a F2 or F3 part number, it should work. When you disconnect the one on your car, disconnect the battery and let it sit for a bit to make sure the thing is discharged. No use blowing the bomb up trying to service the controller.

[Mealticket]

Sly - a '95 at the yard had a black box, not blue, but I thought it was the airbag control module. I found that one of the three wires coming from the front sensors had continuity to several of the pins at this black box, so assumed it was correct. However, the P/N, F5AF-3B494-AC, apparently calls it out as an air suspension module. Not the F2 or F3 you speak of. If it isn't the right box, why do the front sensors have wires going to it? The wire that goes to that unit appears to be purple with a tracer; tracer blue on drivers side, green on pass side...I don't have a decent wiring diagram. Tomorrow I will work on the '93 and see what that has. Guess it will be blue...the '92 at the yard did have a blue box but I didn't get the P/N from that one,

Mealticket

[miamibob]

The box on my Dad's '93 GM was BLUE!

[sly]

+1 the blue box is the correct one. Part number F2AF14B056BD on the one I pulled from a yard. It was in a 93. So it should be in 92 as well since it has a 92 part number.

[SVT98t]

Correct.
FYI, that silver box under the front valance in the middle is the ABS module. Pretty dumb spot for it if you ask me.
(I remember pulling an air bag sensor at EZ-Pull during ScottFest........)


-ryan s.

[Mealticket]

Thanks, guys. I'll get into the '93 today and then probably go back for the '92 box at the yard today/tomorrow,

Mealticket

[Mealticket]

Okay; there has been a blue box sighting. And extraction. Unfortunately no P/N; maybe a sticker came off. It's only been 21 years...cracking it open, I see a white and black plastic cover which based on a video I watched should house the thermal fuse along with a resistor. I can make out some of the numbers on that cover. Turning the PCB over, I can probe the soldered pins and get no continuity on the outer pins, which I understand to be the fuse in question. Good. Probing the inner pins, I get 18 ohms. That's the resistor. The PCB has a P/N etched in: part of it is F2AF-14A608-AC. At least I think that's 608. Didn't bring my glasses...I can also take down the P/N from the biggest chip on the board, a Motorola piece. It would be nice if that chip matches whatever I get at the yard as that seems like the primary component on the board. Yard trip tomorrow,

Mealticket

[sly]

if there's no continuity on the outer pins, that one has the same problem as yours.

[Mealticket]

I've only tested mine, not the one at the yard yet. I should know in a couple of hours,

Mealticket

[sly]

ah ok. good luck then.

[Mealticket]

Well, came home empty handed. Unit in the '92 had P/N F2AF14B056AB, very similar to the one Sly referenced. Under that P/N it said F2AF14B056BB with foam...there was a funny symbol next to both that maybe was a check box, yet neither box was checked. There was a foam piece attached to the box. That suffix therefore is probably some insignifcant callout. Or not. The Motorola chip P/N didn't match, and there was no plastic cover over the thermal fuse and resistor. There was continuity between the soldered pins for the thermal fuse. Good; that validates my testing. The other, smaller Motorola chip P/N didn't quite match either. Big Motorola chip said 1990 Ford. Odd; car had manuf. date of 3-91. My Dad validated the '92 model year by the VIN callout of N, but maybe it was early enough that differences exist. The etched P/N on the PCB was F2AF-14A608-AB; this is again, suffix slightly different, and scary. The pinout looked identical. I figure it would probably work but I'm not comforable with probably on airbags...no experience whatsoever with that. I'll wait for a '93 with identical P/Ns,

Mealticket

[sly]

it probably would have worked if it had the same pin connector. I know there's a couple of different boards that will work. The older one was known for the caps (backup supply) needing to be replaced though.

Also, I have a spare thermal fuse to replace the dead one and the means to solder it in without blowing the fuse if you want to send me the one from your car along with a yuppy food stamp ($20). I'll return it the way it was shipped to me within 2 business days (barring life happening).