Circuit Description

When ignition is first turned on, SDM performs tests to diagnose critical malfunctions within itself. Next SDM measures IGNITION 1 and deployment loop voltages to make sure they are in correct ranges. SDM then proceeds with RESISTANCE MEASUREMENT test. During one portion of RESISTANCE MEASUREMENT test, SDM does following:

• Grounds PASSENGER-SIDE LOW terminal No. 3 through internal current sink.
• Connects PASSENGER-SIDE LOW terminal No. 4 to internal constant current source. This current produces proportional voltage drops in deployment loop.
• Measures voltage difference between PASSENGER-SIDE HIGH and PASSENGER-SIDE LOW.
• Calculates resistance of passenger deployment loop using measured voltage.