DTC 21

Circuit Description
When the ignition switch is turned ON, the sensing and diagnostic module (SDM) will perform tests to diagnose critical malfunctions within itself. Upon passing these tests, Ignition 1 and deployment loop voltages are measured to ensure that they are within their respective normal voltage ranges. The SDM then proceeds with the resistance measurement test. Driver low terminal 3 is grounded through a current sink. The driver current source is connected to the driver high terminal 2 to allow a known amount of current to flow. By monitoring the voltage difference between driver high and driver low, the SDM calculates the combined resistance of the driver inflator module, the clockspring, the harness wiring, and the connector terminal contacts.

DTC 21
DTC 21 will set when the resistance of the driver deployment loop is above a specified value. The test is run once each ignition cycle during the resistance measurement test when the following conditions exist:
- No higher priority faults are detected when the ignition is turned ON.
- Ignition 1 voltage is above a specified value.

When the DTC 21 is set, the SDM will turn on the AIRBAG indicator.

DTC 21 will clear when the ignition switch is turned OFF or the scan tool CLEAR CODES command is received.

Diagnostic Aids
An intermittent condition is likely to be caused by a poor connection from the driver airbag to the clockspring, the clockspring to the steering column connector, or SDM terminals 2 or 3. The test for this DTC is run only while the AIRBAG indicator is performing the turn-on test. When a scan tool CLEAR CODES command is issued and the malfunction is still present, the DTC will not reappear until the next ignition cycle.

Test Description
The numbers below refer to steps on the diagnostic table.
2. Refer to the first caution below.
11. Refer to the third caution below.

Steps 1 - 7:

Steps 8 - 11:

DTC 21 - Driver Deployment Loop Resistance High

CAUTION: The sensing and diagnostic module (SDM) can maintain sufficient voltage to deploy the airbags for 10 minutes after the ignition is OFF and the fuse has been removed. If the airbags are not disconnected, do not begin service until 10 minutes have passed after disconnecting power to the SDM. Otherwise, injury could result.

CAUTION: Never measure the resistance of an inflator module with an ohmmeter. The ohmmeter battery could unexpectedly deploy the airbag which would created the possibility of severe injury and would require the replacement of otherwise useable components.

CAUTION: During service procedures, be very careful when handling the SDM. Never strike or jar the SDM. Never power the supplemental inflatable restraints (SIR) system when the SDM is not rigidly attached to the vehicle. All SDM mounting bolts must be carefully tightened, and the SDM arrow must be pointing toward the front of the vehicle to ensure proper operation of the SIR system. The SDM could be activated if it is powered when it is not rigidly attached to the vehicle, resulting in unexpected deployment and possible injury.

Important: Be careful not to spread or deform the terminals of the clockspring connector.