Chart 1

Code 21 (Chart 1):

DERM Circuit Detail:

DESCRIPTION:

The DERM injects a current of 75 milliamperes through the steering column from the Force Hi output (terminal A4) to the Force Low input (terminal A10). By monitoring the voltage at the Sense Hi input (terminal A7) and the Sense Low input (terminal A6) the DERM calculates the combined resistance of the Inflator Module, SIR Coil, harness wiring (CKTs 347A, 348A) and connector terminal contact in the steering column. Code 21 will set if the resistance is greater than a specified value or the 100 ohm resistors within the Resistor Module is shorted.

TEST CONDITIONS:

Tested once each ignition cycle during the "Steering Column Resistance Test" if:

1. No faults are detected during "Turn-on".
2. No faults are detected during "Continuous Monitoring" for 1 second.
3. No Crank signal present.

FAILURE CONDITIONS:

Code 21 will set if the combined resistance of the Inflator Module, SIR Coil, harness wiring and connector terminal contact in the steering column is greater than a specified value.

CONDITIONS TO CLEAR:

Current Code 21 will be cleared each time the Ignition Switch is turned OFF and the fault is corrected.

NOTES ON FAULT TREE:

1. Checks if fault is in steering column. The SIR Load Tester simulates the resistance of good steering column wiring and components.

2. Determines if fault is in Inflator Module or in the SIR Coil. The SIR Load Tester simulates the resistance of a good Inflator Module.

3. Checks for short in harness or Resistor Module.

4. Determines if short is in harness or Resistor Module.