Abstract: A method and apparatus are disclosed for testing a dual airbag passive restraint system of the type having two firing circuits, each with a series connection of several circuit components including at least two inertia sensors connected in series with a squib across a source of electrical energy, each inertia sensor having a normally open switch and an associated parallel connected resistor. The apparatus comprises a series connected diode and two switching circuits for each firing circuit for isolating at least one of the inertia sensors in each of the firing circuits from other circuit components of its associated firing circuit. A microcontroller monitors at least one voltage value at a component connection while at least one inertia sensor in each firing circuit is isolated. The microcontroller determines a value functionally related to the resistance of at least one circuit component in each firing circuit while at least one inertia sensor is isolated.

Abstract: A test circuit for an airbag restraint system is disclosed and provides an accurate determination of the operativeness of a storage capacitor and calculates the resistance of inertia switch resistors. The capacitor is tested by discharging and charging the capacitor. The values of the inertia switch resistors are determined by switching known resistive values in parallel with the inertia switch resistors. Based on the monitored voltage values during the switching, resistance values are calculated.

Abstract: The apparatus for driving and monitoring a lamp includes a main drive circuit, a backup drive circuit, a monitoring circuit, all connected to a controller. If the controller determines that the main drive circuit cannot energize the lamp, the backup circuit is enabled to energize the lamp. For purposes of energizing the lamp, the lamp is connectable to one of two electrical ground references. If one of the ground references becomes open circuited from the remainder of the circuitry, then the lamp is energized through the other ground reference.

Abstract: A test circuit for an airbag restraint system provides an accurate determination of the operativeness of a storage capacitor and calculates the resistance of inertia switch resistors. The test circuit provides for parallel testing of the storage capacitor and inertia resistors. The capacitor is tested by discharging and charging the capacitor. The values of the inertia switch resistors are determined by switching known resistive values in parallel with the inertia switch resistors. Based on the monitored voltage values during the switching, resistance values are calculated.

Abstract: An impedance measurement circuit and method is disclosed that uses a differential amplifier to amplify a DC voltage value developed across a device being measured. The device is biased between potentials of a source of electrical energy by first and second bias resistors. A switchable current source is connected to the device to, when actuated ON, connect the device to the source of electrical energy through first and second associated resistors. The ratio of the values of the first to second bias resistors is substantially equal to the ratio of the values of the first to second resistors associated with the switchable current source. A microcomputer calculates the resistance of the device by subtracting the value of the output signal from the differential amplifier when the switchable current source is OFF from the value when the switchable current source is ON.