DTC 21 - Driver Initiator Circuit Resistance High

Every time ignition switch is turned to ON position, SDM performs a series of self tests to check for internal malfunctions. If no internal faults are detected, SDM measures voltages in ignition 1, 36 VLR (back-up power supply), and deployment loop circuits. If all of these circuit voltages are within pre-defined parameters, SDM will measure resistance of driver-side inflator module. This is accomplished by allowing a small amount of current to flow from A1 terminal, through driver-side inflator module and back to SDM via A2 terminal. Voltage drop between two terminals is used to calculate resistance of inflator module. In order for SDM to set DTC 21, certain criteria must be met.

• Resistance in driver-side inflator module circuit must be greater than specified.
• No higher priority malfunctions were detected during previous self tests.
• No crank signal is present.

If this fault is occurring intermittently, most probable causes are a poor connection at SDM or driver-side inflator module, or a damaged wire or terminal in SIR wiring harness.

1. Discriminates between a faulty driver-side inflator module and a damaged SIR wiring harness.
2. Validates integrity of Green/Red wire between terminal A1 of SDM and terminal D3 of driver-side inflator module.
3. Validates integrity of Green wire between terminal A2 of SDM and terminal D4 of passenger-side inflator module.
4. Discriminates between a faulty driver-side inflator module and a faulty SIR coil assembly.

Fig 1: DTC 21 - Driver Initiator Circuit Resistance High

Courtesy of GENERAL MOTORS CORP.