How to: Repair an SRS (airbag) module.

As our vehicles age, so does its systems. Parts are hard to find, and whatever is still available is either used or expensive. The manufacturer always recommends replacing parts as a whole instead of replacing an individual failed component. Here's a relatively simple & cheap repair for an expensive, and hard to find module. The SRS (supplemental restraint system) or better known as the airbag module has an internal component called a thermal fuse. This part will blow for various reasons such as old age, vibration, excessive heat from a short or a failure which will cause the internal 15 Ohm resistor to over heat.

Let's get started with the basic removal of the module. It's located under the dashboard on the driver's side in the Aerostar next to the chime module:

This is the module with the case removed:

Here's a close up view of the circuit board:

The part that has to be opened is on the right hand side of the photo above. It contains a 15 Ohm resistor, and a 167* C thermal fuse which are thermally connected by a copper clip inside the plastic housing. Here's an internal view with the case removed:

The thermal fuse is on the top, and the 15 Ohm resistor is on the bottom. Heat rises, so the heat from the resistor will cause the thermal fuse to blow if there's a fault. The internal copper heat sink helps transfer heat. This concludes the removal & tear down process of the module. The next installment explains how to replace the burned out thermal fuse.

We're back again with the next installment which deals with replacing the thermal fuse:

The fuse is soldered into place, so removing the old fuse requires desoldering. Use a plier to pull slightly on the fuse while heating up the solder on the bottom of the printed circuit board. Here's the new thermal fuse:

I was lucky enough to find 4 of these on EBay for $2 with free shipping. One local appliance parts store wanted $5 for just one piece. Always use a heat sink clip on the lead of heat sensitive components while soldering:

The new part is installed, and the case is ready to be closed after the part is tested with an Ohmmeter:

This part didn't have thermal heat sink grease so I didn't add any.
I recommend reading these two PDFs which I found during a Google search for further information: