For 1990-2009 cars

### Circuit Description

When the ignition switch is first turned ON, the SDM will perform tests to diagnose critical malfunctions within itself. Upon passing these tests "Ignition 1", VLR, and deployment loop voltages are measured to ensure they are within their respective normal voltage ranges. Then SDM then proceeds with the "Current Source Diagnostics" "Driver Side LO" terminal A3 is grounded through a resistor and the driver current source connected to "Driver Side HI" terminal A2 allows a known amount of current flow. By monitoring the voltage difference between "Driver Side HI" and "Driver Side LO" the SDM calculates the combined resistance of the driver inflator module, SIR coil assembly, harness wiring circuits 347 and 348 and connector terminal contact.

### DTC Will Set When

The combined resistance of the driver inflator module, harness wiring circuits 347 and 348 and connector terminal contact is greater than 4.5 ohms. This test is run once each ignition cycle during the "Current Source Diagnostics" when:

1. No "higher priority faults" are detected during "Turn-On."
2. No "higher priority faults" are detected during "Continuous Monitoring."
3. "ignition 1" voltage is above a specified value.

### Action Taken

SDM turns ON the AIR BAG telltale lamp and sets, DTC B1021.

### DTC Will Clear When

The malfunction is no longer occurring and the ignition switch is turned OFF, or a Scan Tool "Clear Codes" command is issued.

### Diagnostic Aids

An intermittent condition is likely to be caused by a poor connection at terminals A or B of the SIR coil connector at the base of the steering column, terminals A or B of the driver inflator module connector at the top of the steering column, SDM terminals A2 or A3 of a poor wire to terminal connection in circuit 347 or 348. The test for this diagnostic trouble code is only run while the AIR BAG telltale lamp is performing the bulb check, unless DTC B1017 or DTC B1026 is detected. 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.

When measurements are requested in this chart use SA 91114NE DVM with correct terminal adapter from SA 9206Z. When a check for proper connection is requested refer to Intermittent and Poor Connections. When a wire connector or terminal repair is requested, use the proper repair parts and refer to Wiring Repairs .

### DTC Chart Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This test determines whether the malfunction is occurring in the driver inflator module circuitry or the SDM wiring harness circuitry.

2. This test checks whether the malfunction is due to high resistance in circuit 347.

3. This test checks whether the malfunction is in the driver inflator module or the SIR coil assembly.

4. This test checks whether the malfunction is due to high resistance in circuit 348.

Step | Action | Yes | No
--- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - SIR? | Go to Step 2 | Go to SIR Diagnostic System Check
2 |

1. Turn OFF ignition.
2. Disconnect the driver and passenger inflator module, yellow two-way connectors located at the base of the steering column and under the I/P top cover.
3. Check for proper connection to SIR soil assembly connector at terminals A and B.
4. If not OK, repair and go to Step 9
5. If OK, then connect SA 9409Z-A SIR driver/passenger load tool to driver and passenger inflator module harness connectors.
6. Turn ON ignition.

Is DTC B1021 current?

Go to Step 3

Go to Step 4

3 |

1. Turn OFF ignition.
2. Disconnect SIR driver/passenger load tool.
3. Disconnect SDM.
4. Check for proper connection to SDM at terminals A2 and A3.
5. If not OK, then measure resistance from SDM harness connector terminal A2 to driver inflator module harness connector terminal A.

Is resistance 1 ohm or less?

Go to Step 5

Go to Step 6

4 |

1. Turn OFF ignition.
2. Disconnect SIR driver/passenger load tool from driver inflator module harness connector.
3. Remove inflator module from steering wheel. Refer to Driver Inflator Module .
4. Check for proper connection to driver inflator module from SIR coil assembly connector.
5. If not OK, repair and go to Step 9
6. If OK, connect SIR driver/passenger load tool to inflator module connector at steering wheel.
7. Reconnect driver inflator module harness connector at the base of the steering column.
8. Turn ON ignition.

Is DTC B1021 present?

Go to Step 7

Go to Step 8

5 | Measure resistance from SDM harness connector terminal A3 to driver inflator module harness connector terminal B. Is voltage 1 ohm or less? | Go to Chart A | Go to Step 9
6 | Repair high resistance or open in circuit 347. Go to step 10 | -- | --
7 |

1. Turn OFF ignition.
2. Replace SIR coil assembly. Refer to SIR Coil Assembly.

Go to Step 10

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8 |

1. Turn OFF ignition.
2. Replace driver inflator module. Refer to Driver Inflator Module.

Go to Step 10

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9 | Repair high resistance or open in circuit 348. Go to Step 10 | -- | --
10 |

1. Reconnect all SIR system components. Ensure all components are properly mounted.
2. Clear SIR diagnostic trouble codes.
3. Repeat SIR Diagnostic System Check.

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