Airbag Module Failures - Notice

Due to a recent failure of my own airbag ECU in my 1995 F355, I have also recently learned that this failure is common in F355 models, as well as possibly other Ferrari models. As I am familiar with the design and manufacture of such Automotive Electronics I plan to investigate this further to see if I can identify the exact or probable cause. It is my theory and opinion that this may be due to a circuit design that is unable to handle certain low voltage conditions. I have not yet concluded a failure analysis of my own module, but plan to do so. However, after discussing this situation with knowledgeable Ferrari service technicians, and understanding how and when these failures seem to occur, I'd like to offer the following recommendation to anyone with an airbag-equipped Ferrari.

This problem is commonly noticed when a vehicle has been started or attempted to start with a low battery. During the "key on cycle", the airbag module is attempting to charge up an internal capacitor in the airbag ECU that stores energy for firing the airbag(s) in the event the battery supply is taken out in a crash. This charging is often taking place while the engine is cranking. In the case of a low battery, the drain from the starter, pulls the operating voltage even lower, and may cause it to drop below the operating limits of the airbag ECU, thus causing certain components in the ECU to exceed their operating limits, and potentially fail. Most properly deisgned automotive ECU's are designed to protect against such failures, however.

Thus, to reduce the potential for such failure, I suggest and recommend the following procedure. Before cranking your Ferrari, turn the key to "ON" (but not START), and wait several seconds for the airbag diagnostic light to illuminate, and then fully extinguish, thus indicating the system is ready, and the internal capacitor is charged. Then, continue on to the "START" position to crank the engine. This may minimize the opportunity for failure of the airbag ECU. However, if you notice your battery is low, and your lights seem dim, DO NOT attempt to start the car before fully charging the battery.

In my case, I did not notice any evidence that my battery was low, and the airbag ECU failed on what seemed a normal startup. So, there may be other failure modes in play.

Note: If your airbag light on the instrument panel is illuminated all the time, it is possible that you have an airbag ECU failure. However, there are other components that could also fail to cause the light to illuminate. If the light is illuminated, I recommend you take your car to a service facility capable of reading the diagnostic codes to determine if you have an airbag ECU failure.

In any case, a fully functioning airbag is a required safety device, and the ECU should be robust to withstand normal operation. If you have experienced such a failure, I suggest you report it to the NHTSA Safety Hotline at www.nhtsa.gov. If this is a very common problem, and enough reports are made, then the NHTSA will open an investigation and determine if Ferrari is required to recall and/or replace these components. It would be interesting to see how many of you on FerrariChat have experienced this problem.

Myles H. Kitchen
1995 F355GTS