Normal Operation

The Restraints Control Module (RCM) continuously monitors the driver seat side air bag module and circuits for the following faults:

• Resistance out of range
• Unexpected voltage
• Short to ground
• Faulted driver seat side air bag module

If a fault is detected, the RCM  stores DTC B0020:11, B0020:12, B0020:13 or B0020:1A in memory and sends a message to the Instrument Panel Cluster (IPC) module to illuminate the air bag warning indicator.

The RCM  analyzes the deployment loop resistance and uses this measurement in combination with an age correction factor to determine if a fault exists. The value displayed in the PID is the deployment loop resistance as measured by the RCM  . If the value displayed is lower or higher than the desired range (refer to diagram below), the RCM  can set a DTC. As the deployment loop resistance drifts farther outside the desired range, the chance for a DTC increases. The RCM  fault trigger threshold may vary as the vehicle ages. Small variations in resistance can occur due to the effect of road vibrations on terminal fit and/or temperature changes. 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
• Driver seat side air bag module
• RCM 
  Fig 1: Air Bag Warning Indicator Pinpoint Test Flow Diagram

  Courtesy of FORD MOTOR CO.

This pinpoint test is intended to diagnose the following: 

• Wiring, terminals or connectors
• Driver seat side air bag module
• RCM