Airbag thermal fuse replacement, important corrective repair information! | Ford Explorer Forums - Serious Explorations

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Airbag thermal fuse replacement, important corrective repair information!


New Member
April 29, 2024
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City, State
San Diego CA
Year, Model & Trim Level
1992 cargo 3.0
It is possible that your airbag can be disabled without any blink code warning if a repair isn't correctly done!
This is because the thermal fuse replacement proposed here and by others online is a standard 4mm diameter that doesn't fit in its intended case. The original is a 3mm diameter that only works because of its physical contact with a 'trip' resistor in a small enclosed box where trip heat doesn't dissipate.

Here is some detail on the module function and information for a safe and reliable repair.

My '92 Aerostar airbag module F2AZ-14B056-A was displaying false errors due to bad corrosive leaking electrolytic capacitors.. new caps and jumper wires fixed that problem. After the repair I had the 51 code, open thermal fuse, I think because I moved the van without the airbag installed. Looks like several vehicles use a similar module.

1) The 40 pin IC on this board will detect a fault from various sources and so turn on a power transistor which connects a ~ 15 ohm resistor to RUN +12 volts supplied at connector C233-1. This resistor is the heat source used to open a 168°C fuse which when blown open sets off the 51 blink code. This resistor has no other function. Unless there is an airbag circuit fault no current flows thru it.

2) The original thermal fuse was marked 168°C but I couldn't read an amp rating. I measured under 1milliamp running thru the fuse under normal running conditions and so used a 0.2 amp fuse for testing purposes. No problem. Many thermal fuses are rated several amps or more, this is also fine to use since its application is only caring about the temperature of the resistor and supplying a tiny current to the control circuits.

I found a 2 amp 145°C 3mm x 9mm axial lead fuse on ebay. It will snap in place inside its box with snug fit against the 15 ohm resistor. The placement inside the box allows heat to trip the fuse. The resistor is a wire wound special high wattage type that is not critical +/- a couple of ohms. Melted fuse/resistor cases pictured on this or other forums must be from wrongly modified circuits, don't do that. I don't believe the temp rating is at all critical, 168° or reasonably less should be okay. Your can test if the fuse is ok without removing module by removing harness wiring and reading a diode drop across the connector C233 pin 13 & 15.

Backup "Battery" on this module is x4 220mfd/25v capacitors. Once car Battery is disconnected the backup 12v from the caps discharges quickly to 3v in one minute, < 1v in 2 min. Module is safe to handle after 2 min. The caps charge over a couple of minutes whenever the car battery is connected via C233-13 Always Hot 12v.

Pictures are from 1992 Aerostar electrical and vacuum manual, and my board with test parts installed. You can see where solder mask was removed to repair leaking capacitor damage.


Welcome to this forum! Your thread was moved into the Aerostar section. Thanks for posting this information.
Thank you BrooklynBay! The same airbag module is used on Explorer and other models I believe. I won't be around here much since our '92 will be for sale in June, my TV repair business no longer does house calls.
I didn't know there would be a forum and am interested in your persistence here and your stable full of vans. My van is a rugged little workhorse that needs so little care or repair. I'll miss it.