Abstract: A diagnostic method (100) with pre-assembly fault recording lock-out inhibits fault recording during assembly of a main system until the system has been determined operation at least once (116). The method will still note the detection of system failures/errors (112) by activating a warning lamp (120), but will not record these faults into memory until the system has determined that the main system has been powered up without any errors at least once (118 and 122). Thus, since these faults are not stored in memory during manufacture/assembly, the method of the present invention obviates the need for any additional assembly step(s) of erasing and/or clearing the memory, or externally controlled recording inputs for the diagnostic system.

Abstract: A circuit for generating a regulated negative voltage output pulse for use in calibrating a transducer, such as used in sensing an acceleration profile of a moving object, comprises a transistor responsive to a periodically generated control pulse for reversing the polarity charge on a capacitor. A negative voltage charge on the capacitor activates a negative voltage regulator to generate the desired regulated negative voltage calibration pulse. A pair of resistors are series connected to the regulated negative voltage output and a positive voltage reference source to provide an output for an external monitoring device to verify the generation of an accurate regulated negative voltage calibration pulse. The pair of resistors also provide a bypass of the negative voltage regulator when no external control pulse is present, thereby establishing a positive voltage output for the calibration pulse generating circuit when a regulated negative voltage calibration pulse is not being generated.

Abstract: An air bag firing circuit comprises a firing path which includes in series a safing sensor, a squib, and a FET operated under microprocessor control in response to the output of an electronic crash sensor. A power supply maintains a known voltage across the firing path sufficient to explode the squib upon simultaneous "closure" of both the safing sensor and the FET operated by the microprocessor in response to crash sensor output. Normally, upon detection of a failure in the electronic crash sensor, its supporting electronics, or the FET actuated in response thereto, the microprocessor reconfigures the firing threshold of the safing sensor, as by applying a current to its integral test coil to increasingly bias the sensor's inertial mass away from its switch contacts. However, if a failure of the safing sensor is detected, reconfiguration of its threshold is inhibited notwithstanding the failure of other circuit components to prevent inadvertent deployment of the air bag.