For 1990-2009 cars
SIR Components
SIR Schematics
SIR Caution
Handling ESD Sensitive Parts Notice
SIR Caution
SIR Caution

### Circuit Description

When you first turn the ignition switch to the ON position, the inflatable restraint sensing and diagnostic module (SDM) performs tests to diagnose critical malfunctions within itself. Next the SDM measures IGNITION 1 and the deployment loop voltages to make sure they are within their respective normal voltage ranges. Then the SDM proceeds with the RESISTANCE MEASUREMENT test. During one portion of the RESISTANCE MEASUREMENT test, the SDM does the following:

• | Grounds the DRIVER SENSE LOW terminal 3 through an internal current sink.

• | Connects the DRIVER SENSE HIGH terminal 2 to an internal constant current source. This current produces proportional voltage drops in the deployment loop.

• | Measures the voltage difference between DRIVER SENSE HIGH and DRIVER SENSE LOW.

• | Calculates the resistance of the driver deployment loop using the measured voltage.

### Conditions for Setting the DTC

• | The driver and passenger deployment loops are not open.

• | The driver and passenger deployment loops are not shorted to voltage.

• | The driver deployment loop is not shorted to ground.

• | The driver deployment loop resistance is more than 3.8 ohms. The driver deployment loop consists of the following components:

- | Inflatable restraint steering wheel module.

- | Inflatable restraint steering wheel module coil.

- | Harness wiring of CKT 347.

- | Harness wiring of CKT 348.

- | Connector terminal contact.

The RESISTANCE MEASUREMENT test checks for this malfunction. This test only occurs once each ignition cycle when IGNITION 1 is within the normal operating voltage range.

### Action Taken When the DTC Sets

• | The SDM sets a Diagnostic Trouble Code.

• | The SDM turns ON the AIR BAG warning indicator.

### Conditions for Clearing the DTC

The DTC will clear when one of the following conditions is met:

• | Current DTC

| The resistance of the driver deployment loop is less than 3.8 ohms and the ignition switch is cycled.

• | History DTC

- | You issue a scan tool CLEAR CODES command.

- | Once 250 malfunction free ignition cycles have occurred.

When you issue a scan tool CLEAR CODES command and the malfunction is still present, the DTC will not reappear until the next ignition cycle.

### Diagnostic Aids

A poor connection can cause an intermittent condition. Check the following for a poor connection:

• | The inflatable restraint steering wheel module steering column connector terminals A and B.

• | The upper inflatable restraint steering wheel module coil connector terminals A and B.

• | The SDM terminals 2 and 3.

• | The wire to terminal connections in CKT 347.

• | The wire to terminal connections in CKT 348.

The diagnostic table directs the technician to note the entry value of DRIVER RESISTANCE. Comparing the value of DRIVER RESISTANCE over multiple ignition cycles can be helpful in determining if an intermittent condition exists.

When measurements are requested in this table, use the J 39200 DMM with the correct terminal adapter from the J 35616 Connector Test Adapter Kit. When an inspection for proper connection is requested, refer to Testing for Electrical Intermittents in Wiring Systems. When a wire, connector or terminal repair is requested, use the J-38125 Terminal Repair Kit and refer to Wiring Repairs in Wiring Systems.

### Test Description

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

1. This test determines the deployment loop resistance measured by the inflatable restraint Sensing and Diagnostic Module (SDM).

2. This test checks for proper contact or corrosion of the yellow 2-way connector.

3. This test isolates the malfunction to one side of the inflatable restraint steering wheel module yellow 2-way connector.

4. This test determines whether the malfunction is due to the inflatable restraint steering wheel module or the module coil.

5. This test checks for proper contact or corrosion of the SDM connector.

6. This test determines whether the malfunction is in CKT 347.

7. This test determines whether the malfunction is in CKT 348.

#### DTC B1021 Driver Deployment Loop Resistance High

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the SIR Diagnostic System Check performed? | -- | Go to Step 2 | Go to SIR Diagnostic System Check
2 |

1. Turn the ignition switch to the OFF position.
2. Connect a scan tool to the DLC.
3. Turn the ignition switch to the ON position.
4. Request the SIR data list display.
5. Read and record on the repair order the driver deployment loop resistance DRIVER RESISTANCE.

Has the DRIVER RESISTANCE been read and recorded on the repair order?

--

Go to Step 3

--

3 |

1. Turn the ignition switch to the OFF position.
2. Disconnect the inflatable restraint steering wheel module yellow 2-way connector located inside the LH I/P wiring harness junction block.
3. Disconnect the inflatable restraint I/P module yellow 2-way connector located inside the RH I/P wiring harness junction block.
4. Check for proper connection at terminals A and B on the harness side of the inflatable restraint steering wheel module (driver inflator module) yellow 2-way connector located inside the LH I/P wiring harness junction block.

Are the terminals damaged or corroded?

--

Go to Step 4

Go to Step 6

4 | Replace the yellow 2-way harness connector located inside the LH I/P wiring harness junction block. Refer to Wiring Repair . Are the repairs complete? | -- | Go to Step 5 | --
5 | Check for proper connection at terminals A and B of the inflatable restraint steering wheel module coil (SIR coil assembly) side of the connector. Are the terminals damaged or corroded? | -- | Go to Step 7 | Go to Step 23
6 | Check for proper connection at terminals A and B of the inflatable restraint steering wheel module coil (SIR coil assembly) side of the connector. Are the terminals damaged or corroded? | -- | Go to Step 7 | Go to Step 8
7 | Replace the inflatable restraint steering wheel module coil (SIR coil assembly). Refer to Inflatable Restraint Steering Wheel Module Coil Replacement . Are the repairs complete? | -- | Go to Step 23 | --
8 |

1. Connect the inflatable restraint steering wheel module yellow 2-way connector located inside the LH I/P wiring harness junction block.
2. Connect the inflatable restraint I/P module yellow 2-way connector located inside the RH I/P wiring harness junction block.
3. Turn the ignition switch to the ON position.
4. Using the scan tool, request the SIR data list display.
5. Read the driver deployment loop resistance DRIVER RESISTANCE.

Is DRIVER RESISTANCE greater than the specified value?

3.8 ohms

Go to Step 10

Go to Step 9

9 | Replace the yellow 2-way harness connector located inside the LH I/P wiring harness junction block. Refer to Wiring Repair . Are the repairs complete? | -- | Go to Step 23 | --
10 |

1. Turn the ignition switch to the OFF position.
2. Disconnect the inflatable restraint steering wheel module yellow 2-way connector located inside the LH I/P wiring harness junction block.
3. Disconnect the inflatable restraint I/P module yellow 2-way connector located inside the RH I/P wiring harness junction block.
4. Connect J 38715-A SIR Driver/Passenger Load Tool to the harness connectors.
5. Turn the ignition switch to the ON position.
6. Using the scan tool, request the data list display.
7. Read the driver deployment loop resistance DRIVER RESISTANCE.

Is DRIVER RESISTANCE greater than the specified value?

3.8 ohms

Go to Step 14

Go to Step 11

11 |

1. Turn the ignition switch to the OFF position.
2. Remove the inflatable restraint steering wheel module. Refer to Inflatable Restraint Steering Wheel Module Replacement .
3. Disconnect J 38715-A from the driver 2-way harness connector.
4. Connect the 2-way connector located inside the LH I/P wiring harness junction block.
5. Connect J 38715-A to the upper inflatable restraint steering wheel module coil connector at the top of the steering column.
6. Turn the ignition switch to the ON position.
7. Using the scan tool, request the SIR data list display.
8. Read the driver deployment loop resistance DRIVER RESISTANCE.

Is DRIVER RESISTANCE greater than the specified value?

3.8 ohms

Go to Step 13

Go to Step 12

12 |

1. Turn the ignition switch to the OFF position.
2. Replace the inflatable restraint steering wheel (driver inflator) module. Refer to Inflatable Restraint Steering Wheel Module Replacement .

Are the repairs complete?

--

Go to Step 23

--

13 |

1. Turn the ignition switch to the OFF position.
2. Replace the inflatable restraint steering wheel module coil. Refer to Inflatable Restraint Steering Wheel Module Coil Replacement .

Are the repairs complete?

--

Go to Step 23

--

14 |

1. Turn the ignition switch to the OFF position.
2. Disconnect the inflatable restraint Sensing and Diagnostic Module (SDM). Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement .
3. Disconnect J 38715-A .
4. Check for proper connection at terminal 2 and terminal 3 on the harness side of the SDM connector.

Is the connector damaged or corroded?

--

Go to Step 15

Go to Step 17

15 | Replace the SDM harness connector. Refer to Wiring Repair . Are the repairs complete? | -- | Go to Step 16 | --
16 | Check for proper connection at terminal 2 and terminal 3 on the SDM. Are the terminals damaged or corroded? | -- | Go to Step 18 | Go to Step 23
17 | Check for proper connection at terminal 2 and terminal 3 on the SDM. Are the terminals damaged or corroded? | -- | Go to Step 18 | Go to Step 19
18 | Replace the inflatable restraint Sensing and Diagnostic Module (SDM). Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement . Are the repairs complete? | -- | Go to Step 23 | --
19 |

1. Zero the J 39200 Digital Multimeter.
2. Measure the resistance between the SDM harness connector terminal 2 and the inflatable restraint steering wheel module yellow 2-way harness connector terminal A.

Is the resistance reading within the specified values range?

0-2 ohms

Go to Step 21

Go to Step 20

20 | Repair the high resistance condition in CKT 347. Are the repairs complete? | -- | Go to Step 23 | --
21 |

1. Zero the J 39200 .
2. Measure the resistance between the SDM harness connector terminal 3 and the inflatable restraint steering wheel module yellow 2-way harness connector terminal B.

Is the resistance reading within the specified values range?

0-2 ohms

Go to Sensing and Diagnostic Module Integrity Check

Go to Step 22

22 | Repair the high resistance condition in CKT 348. Are the repairs complete? | -- | Go to Step 23 | --
23 | Reconnect all the SIR system components, make sure all the components are properly mounted. Have all the SIR components been reconnected and properly mounted? | -- | Go to Step 24 | --
24 | Clear all the SIR DTCs. Have all the SIR DTCs been cleared? | -- | Go to SIR Diagnostic System Check | --