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

### Circuit Description

The inflatable restraint Sensing and Diagnostic and Seat Belt Pretensioner Module (SDM) performs tests to diagnose critical malfunctions within itself when the ignition switch is turned ON. The SDM monitors the six firing loops to detect leakage currents to ground and system voltage in the frontal and side air bag inflator module and seat belt pretensioner circuits. The deployment loop resistances are measured to ensure they are within their respective normal resistance ranges. Upon passing these tests, and if the energy reserve is charged up, the firing transistors are tested. The SDM then goes into Continuous Monitoring mode. The SDM service wait time is 1 minute. Refer to On-Vehicle Service for enable/disable procedures.

### Conditions for Setting the DTC

• | The ignition is within normal operating voltage range.

• | The measured leakage currents to system voltage in or the loop resistance of the driver Side Impact Sensor (SIS) loop are above a specified value caused by:

- | A short circuit from the driver Side Impact Sensor (SIS) loop to system voltage.

- | An open circuit or high resistance condition in the driver Side Impact Sensor (SIS) loop.

The driver Side Impact Sensor (SIS) loop consists of the following components:

• | The inflatable restraint Side Impact Sensor (LH) .

• | The harness wiring of CKT B41.

• | The harness wiring of CKT B42.

• | The harness wiring of CKT XB42.

• | The connector terminal contact.

DTC 73 will set once one of these conditions is met. This test is run during the SDM Turn-ON tests.

### Action Taken When the DTC Sets

• | The SDM sets a Diagnostic Trouble Code.

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

### Conditions for Clearing the DTC

Current and History DTC codes must be cleared using a scan tool Clear DTC Information command. If the circuit fault has been successfully repaired and the conditions which caused the Current DTC 73 to set are no longer existing, History DTC 73 will set. History DTC 73 may be cleared using the scan tool.

### Diagnostic Aids

An inflatable restraint driver Side Impact Sensor (SIS) circuit short-to-ground can cause an intermittent condition. Inspect CKTs B41, B42 and XB42 carefully for cutting and/or chafing. A careful inspection of the circuits and components indicated on the DTC 73 Table is essential to make sure that the replacement SDM will not be damaged.

When measurements are requested in this table, use J 39200 Digital Multimeter with the correct terminal adapter from J 35616 Connector Test Adapter Kit. When a check for proper connection is requested, refer to Intermittents and Poor Connections . When a wire, connector or terminal repair is requested, use J-38125 Terminal Repair Kit and refer to Wiring Repair .

### Test Description

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

1. This test determines whether the malfunction is a short to voltage condition in CKT B42 in the LH door electrical harness.

2. This test determines whether the malfunction is a short to voltage condition in CKT XB42 in the LH door electrical harness.

3. This test determines whether the malfunction is a high resistance condition in CKT B42 in the LH door electrical harness.

4. This test determines whether the malfunction is a high resistance condition in CKT XB42 in the LH door electrical harness.

5. This test determines whether the malfunction is a short to voltage condition in CKT B41.

6. This test determines whether the malfunction is a short to voltage condition in CKT XB42 between the LH side door electrical connector and the SDM harness connnector.

7. This test determines whether the malfunction is a high resistance condition in CKT B41.

8. This test determines whether the malfunction is a high resistance condition in CKT XB42 between the LH side door electrical connector and the SDM harness connnector.

#### DTC 73 Driver Side Impact Sensor Open or Short to Voltage

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. Wait 1 minute until the capacitors in the Sensing and Diagnostic and Seat Belt Pretensioner Module (SDM) have discharged.
3. Remove the driver seat back cover. Refer to Seat Back Replacement - Front in Seats.
4. Disconnect the inflatable restraint driver seat module yellow 2-way integral connector.
5. Disconnect the LH door electrical connector C500.
6. Check for proper connection at terminal 39 and terminal 40 on the door side of C500.

Are the terminals damaged or corroded?

--

Go to Step 3

Go to Step 5

3 | Replace the LH door electrical harness. Is the replacement complete? | -- | Go to Step 4 | --
4 | Check for proper connection of terminal 39 and terminal 40 on the harness side of the LH door electrical connector C500. Are the terminals damaged and/or corroded? | -- | Go to Step 6 | Go to Step 27
5 | Check for proper connection of terminal 39 and terminal 40 on the harness side of the LH door electrical connector C500. Are the terminals damaged and/or corroded? | -- | Go to Step 6 | Go to Step 7
6 | Replace the body harness Is the replacement complete? | -- | Go to Step 27 | --
7 |

1. Disconnect the inflatable restraint side impact sensor (LH). Refer to Inflatable Restraint Side Impact Sensor Replacement .
2. Turn the ignition switch to the ON position.
3. Use the J 39200 to measure the voltage from the LH side impact sensor 2-way connector terminal 1 to a known good ground.

Is the measured voltage less than the specified value?

1 V

Go to Step 9

Go to Step 8

8 | Repair the short to voltage in CKT B42 between the LH door side impact sensor 2-way connector terminal 1 and terminal 40 of the LH door electrical connector C500. Is the repair complete? | -- | Go to Step 27 | --
9 | Use the J 39200 to measure the voltage from the LH side impact sensor 2-way connector terminal 2 to a known good ground. Is the measured voltage less than the specified value? | 1 V | Go to Step 10 | Go to Step 11
10 | Repair the short to voltage in CKT XB42 between the LH door side impact sensor 2-way connector terminal 2 and terminal 39 of the LH door electrical connector C500. Is the repair complete? | -- | Go to Step 28 | --
11 |

1. Turn the ignition switch to the OFF position.
2. Wait 1 minute until the capacitors in the SDM have discharged.
3. Zero the J 39200 .
4. Use the J 39200 to measure the resistance from the from the LH side impact sensor 2-way connector terminal 1 to terminal 40 of the LH door electrical connector C500.

Is the resistance reading within the specified values?

0-0.5 ohms

Go to Step 13

Go to Step 12

12 | Repair the high resistance condition in CKT B42. Is the repair complete? | -- | Go to Step 28 | --
13 |

1. Zero the J 39200 .
2. Use the J 39200 to measure the resistance from the from the LH side impact sensor 2-way connector terminal 2 to terminal 39 of the LH door electrical connector C500.

Is the resistance reading within the specified values?

0-0.5 ohms

Go to Step 15

Go to Step 14

14 | Repair the high resistance condition in CKT XB42 between the LH side impact sensor 2-way connector and the LH door electrical connector C500.. Is the repair complete? | -- | Go to Step 28 | --
15 |

1. Disconnect the negative battery cable. Refer to

   Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

   .
2. Disconnect the inflatable restraint Sensing and Diagnostic and Seat Belt Pretensioner Module (SDM).
3. Check for proper connection at terminal 41 and terminal 42 of the SDM harness connector.

Are the terminals damaged or corroded?

--

Go to Step 16

Go to Step 18

16 | Replace the IP harness. Is the replacement complete? | -- | Go to Step 17 | --
17 | Check for proper connection at terminal 41 and terminal 42 on the SDM. Are the terminals damaged or corroded? | -- | Go to Step 19 | Go to Step 28
18 | Check for proper connection at terminal 41 and terminal 42 on the SDM. Are the terminals damaged or corroded? | -- | Go to Step 19 | Go to Step 20
19 | Replace the inflatable restraint Sensing and Diagnostic and Seat Belt Pretensioner Module (SDM). Refer to Inflatable Restraint Sensing and Diagnostic and Seat Belt Pretensioner Module Replacement . Is the replacement complete? | -- | Go to Step 28 | --
20 |

1. Reconnect the negative battery cable.
2. Turn the ignition switch to the ON position.
3. Use the J 39200 to measure the voltage from the SDM harness connector terminal 41 to terminal 7 (ground).

Is the measured voltage less than the specified value?

1 V

Go to Step 22

Go to Step 21

21 | Repair the short to voltage condition in CKT B41 between the body harness side of the LH door electrical connector C500 and SDM harness connector. Is the repair complete? | -- | Go to Step 28 | --
22 | Use the J 39200 to measure the voltage from the SDM harness connector terminal 42 to terminal 7 (ground). Is the measured voltage less than the specified value? | 1 V | Go to Step 24 | Go to Step 23
23 | Repair the short to voltage condition in CKT XB42 between the body harness side of the LH door electrical connector and SDM harness connector. Is the repair complete? | -- | Go to Step 28 | --
24 |

1. Turn the ignition switch to the OFF position.
2. Zero the J 39200 .
3. Use the J 39200 to measure the resistance between the LH door electrical connector terminal 40 and the SDM harness connector terminal 41.

Is the resistance reading within the specified values?

0-0.5 ohms

Go to Step 26

Go to Step 25

25 | Repair the high resistance condition in CKT B41 between the body harness side of the LH door electrical connector and SDM harness connector.. Is the repair complete? | -- | Go to Step 28 | --
26 | Measure the resistance between the LH door electrical connector terminal 39 and the SDM harness connector terminal 42. Is the resistance reading within the specified values? | 0-0.5 ohms | Go to Integrity Check | Go to Step 27
27 | Repair the high resistance condition in CKT XB42 between the LH door electrical connector and the SDM harness connector. Is the repair complete? | -- | Go to Step 28 | --
28 | Reconnect all the SIR components, make sure all the components are properly mounted. Have all the SIR components been reconnected and properly mounted? | -- | Go to Step 29 | --
29 | Clear all the SIR DTCs. Have all the DTCs been cleared? | -- | Go to SIR Diagnostic System Check | --