Chart A History Code Diagnosis

***This Procedure has been Updated by TSB 93-U-10, December 1992***

CIRCUIT DESCRIPTION
When system voltage is applied to the DERM, it will perform "Turn-ON" tests followed by "Continuous Monitoring" tests. If no malfunctions are detected, the DERM will perform a "Steering Column Resistance Test." When a malfunction is detected, the DERM will store a current diagnostic trouble code and illuminate the "AIR BAG" warning lamp. The DERM will clear current diagnostic trouble codes and store them as history diagnostic trouble codes when the malfunction is no longer detected or when the ignition switch is cycled, except for DTC 51. Current DTC 51 can only be cleared with a scan tool and will then be stored as a history diagnostic trouble code. History DTC 51 can be cleared for the current ignition "ON" cycle but will reappear at the next ignition "ON" cycle.

DIAGNOSTIC AIDS
When diagnosing an intermittent DTC 24 ("24 H", indicating History 24), when it is set alone or in combination with any other DTC(s), follow the diagnostic chart of "Current Code 24." However, when diagnosing an intermittent DTC 24, the DERM should NOT be replaced. It is extremely rare for an intermittent problem (History DTC) to be caused by the DERM itself.

DTC 24 can be set by any of the following conditions:
1. A short to ground or B+ on:
^ Either SIR Coil Assembly circuit
^ CKT 347
^ CKT 348
^ CKT 349
^ CKT 688
^ CKT 714
^ CKT 752

2. A short to ground on CKT 753

3. An open in CKT 752

4. Improper resistance in the:
^ Resistor Module
^ Arming Sensor
^ Discriminating Sensor(s)

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. The DERM has detected an event in which the "Sense High" voltage was above a certain percentage of deployment loop voltage and, simultaneously, the "Sense Low" voltage was below a certain percentage of deployment loop voltage.
2. Checks for intermittent conditions within the steering column.
3. Checks for intermittent shorts in the "36 VLR" wiring, CKT 236.
4. Checks for an open GAUGES fuse, open "AIR BAG" warning lamp bulb or uncleared DTC 61 after a completed wiring repair on CKT 39. Also checks for intermittent malfunctions in CKTs 688 and 358.
5. Checks for intermittent opens in the low side of the deployment loop between the discriminating sensors.
6. Checks for intermittent wiring shorts between "36 VLR" CKT 236 and CKTs 347, 348 and 349 of the SIR wiring harness.
7. Checks for intermittent short to B+ in the "36 VLR" wiring CKT 236.
8. Checks for intermittent short to ground in the "36 VLR" wiring CKT 236.
9. Checks for intermittent open in the "36 VLR" wiring CKT 236.
10. Checks for intermittents in the "Force High" and "Force Low" wiring CKTs 714 and 688.
11. Checks for intermittent opens or shorts to ground in the "Sense Low" wiring CKT 752.
12. Checks for shorts to ground in the deployment loop CKTs 347, 348 and 349 or in the diagnostic CKTs 347, 348, 688, 714, 752 and 753.
13. Checks for shorts between CKT 236 and CKTs 347, 348 or 349.
14. Checks for intermittent open in the "36 VLR" wiring CKT 236.
15. Checks for intermittent open between the splice and the arming sensor CKT 1139.