Normal Operation and Fault Conditions

The RCM continuously monitors the passenger air bag module stage 2 circuits for the following faults:

• Resistance out of range
• Unexpected voltage
• Short to ground
• Faulted passenger air bag module

If a fault is detected, the RCM stores DTC B0011:11, B0011:12, B0011:13 or B0011:1A in memory and sends a message to the IPC to illuminate the air bag warning indicator.

The RCM analyzes the deployment loop resistance to determine if a fault exists. The value displayed in the PID is the deployment loop resistance measured by the RCM. If the value displayed is lower or higher than the desired range (refer to Fig 1), the RCM can set a DTC. As the deployment loop resistance drifts farther outside the desired range, the chance for a DTC increases. Small variations in resistance can occur due to the effect of road vibrations on terminal fit. Crimps and terminals can be affected by stress and harness movement and can cause an increase in resistance due to wire strain. These variables can result in an intermittent fault. For this reason, the test requires the PID value to be within the desired range before the fault is considered repaired, regardless if the module is reporting an on-demand DTC at the time of diagnosis. Following this direction helps make sure that minor changes in resistance do not create a repeat concern. This test uses process of elimination to diagnose each part of the deployment loop circuit including:

• Wiring
• Connections
• Passenger air bag module
• RCM

Fig 1: RCM Analyzes Resistance Flow Diagram

Courtesy of FORD MOTOR CO.